CHAPTER VIII

IGNITION SYSTEMS

(73) Principles of Ignition.

It is the purpose of the ignition system to raise a small portion of the mixture to the combustion temperature, or the temperature at which the air and fuel will start to enter into chemical combination. When combustion is once started in a compressed combustible gas it will spread throughout the mass no matter how small the original portion inflamed. The rate at which the flame spreads through the combustion chamber depends upon the compression pressure, the richness of the mixture, the nature of the fuel and upon the number of points at which it is ignited.

In practice perfect ignition is seldom realized. This is due not only to the ignition system itself but to poor mixture proportions, imperfect vaporizing of the fuel, and low compression; all of which tend to a slow burning mixture with the attendant losses.

The best ignition system will be that which will cause the ignition to occur invariably at the point of highest compression and which will supply ample heat to start the process of combustion with a cold cylinder, imperfect mixtures, and low compressions. An efficient and reliable ignition system is without a doubt the most important unit in the construction of a gas engine. As ignition systems have improved and become more reliable, so has the gas engine become more widely used and appreciated, and in almost a direct proportion to these improvements.

Many ingenious ignition systems have been proposed, but only two of these have met with any degree of success in practice; i. e., electrical ignition and ignition by means of the hot tube.

Sponge platinum has the peculiar property of igniting jets of hydrogen gas, or hydrocarbons, without the aid of heat; this is due to the condensing effect of the platinum on these gases.

It was proposed to ignite the gaseous charge of the gas engine by means of the platinum sponge (catalytic ignition) but the system proved a failure because of the clogging of the pores in the sponge by fine particles of soot.

Dr. Otto employed an open flame which was introduced into the mixture by means of a slide valve. This met with only a fair measure of success.

Cerium, Lanthum and several other rare metals cause a considerable spark when brought into contact with iron or steel. The objection to this method was the expense of the Cerium plugs which required frequent renewal.

The writer remembers a quaint attempt at firing the charge by means of a piece of flint and steel; the failure of this is obvious.

The Diesel Engine, a great success from a thermodynamic standpoint, is fired by means of the heat produced by the compression of air, the fuel being sprayed into air which is compressed to several hundred pounds pressure.

Mr. Victor Lougheed proposes ignition by means of a platinum wire rendered incandescent by a current of electricity. The plan sounds feasible, but we are still waiting to be shown.

Electric ignition is applicable to all classes of engines; in fact this system made the variable speed engine as used on automobiles, etc., a possibility, as accurate timing with the electric spark covers the range from the lowest possible speed to speeds of 4,500 revolutions per minute and over.

(74) Advance and Retard.

While the combustion of the mixture is extremely rapid under favorable conditions, there is, nevertheless, a perceptible lapse between the instant of ignition and the final pressure established by the heat of the combustion. For this reason it is necessary that ignition should be started a certain length of time before the pressure is required if we are to expect a maximum pressure at a definite point in the stroke of the piston. The amount by which the time of ignition precedes that of combustion is called the =ADVANCE=, and is usually given in terms of angular degrees made by the crank in traveling from the time of ignition to time of maximum pressure. Since the pressure is always required at the extreme end of the compression stroke, the degree of advance is given as the angle made by the center line of the cylinder with the center line of the crank at the instant of ignition. Should the advance be given as 10°, for example, it is meant that the crank is still 10° from completing the compression when ignition occurs.

Owing to variations in the richness of the mixture, and changes in the compression pressure, due to throttling the incoming charge, the rate of inflammation varies from time to time under varying loads. To keep the maximum pressure at a given point under these conditions it is necessary to vary the point of ignition to correspond with the increase or decrease of inflammation. This variation of advance to meet varying loads is approximated by the governor in some engines, and manually in others. The advance of an automobile is an example of manual ignition control. Should the point of ignition vary from the theoretical point it will result in a loss of fuel and power, and for this reason the ignition should be under at least an approximate control. A wide variation in engine speed has a very considerable effect on the ignition point as there is less time in which to burn the mixture at high piston speeds, and consequently the ignition must be further advanced to insure complete combustion at the end of the stroke. This fact is evident to those who have driven automobiles.

Should the ignition occur too early, so that combustion is complete before the piston reaches the end of the stroke, there will be a loss of power due to the tendency of the pressure to reverse the rotation of the engine. When starting an engine, over-advanced ignition will throw the crank over in the reverse direction from which it is intended to go, and will not only prevent the engine from coming up to speed but will prove dangerous to the operator.

Due to the effects of inertia and self induction in several types of ignition apparatus, a greater advance will be required than that demanded by the combustion rate of the mixture. This sluggishness of the apparatus in responding to the piston position is called ignition =LAG=. The total advance required to have the combustion complete at the end of the stroke is equal to the advance required by the burning speed plus the ignition lag. Since lag is principally due to inertia effects, it is much greater at high speeds than at low, and it therefore causes an additional advance at high speeds. Causing the ignition to occur before the crank reaches the upper dead center is called =ADVANCED IGNITION=, causing it to occur after the piston has reached the upper dead center, or when on the outward stroke, is called =RETARDED IGNITION=.

Ignition is retarded when starting an engine to prevent it from taking its initial turn in the wrong direction. As the combustion takes place after the compression, with the piston moving on the working stroke, in retard, it is impossible for the pressure to force the piston in any direction but the right one. Excessively retarded ignition will cause a power loss and will also cause overheating of the cylinder and valves as the combustion is slower.

(75) Preignition.

Preignition which is in effect the same as over-advanced ignition as due to causes within the cylinder such as incandescent carbon deposits or thin sharp edges in the cylinder that have become incandescent through the heat of the successive explosions. Preignition is very objectionable since it causes heavy strains on the engine parts and causes a loss of power in the same way as over-advanced ignition. Any condition that causes the preigniting of the charge should be removed immediately.

(76) Misfiring.

The failure of the ignition apparatus to ignite every charge is called =MISFIRING=. This missing not only causes a waste of fuel and a loss of power but it also causes an increased strain on the engine parts because of the violence of the explosion following the missed stroke. The heavy explosion is due to the fact that the stroke following the “miss” is more thoroughly scavenged by the two admissions of the mixture than the ordinary working stroke, and consequently contains a more active charge.

(77) Hot Tube Ignition.

A combustible gas may be ignited by bringing it into contact with surface heated to, or above the ignition temperature. It is upon this principle that hot tube ignition is based.

In practice this surface is provided by the bore of a tube which is in communication with the charge in the cylinder, the outer end of the tube being closed or stopped up. Around this tube is an asbestos-lined chimney which causes the flame from the Bunsen burner to come into contact with the tube and also prevents draughts of air from chilling it.

A Bunsen burner is located near the base of the tube and maintains it at bright red heat. The gas for the burner is supplied from a source external to the engine. When the fuel used is gasoline, a gasoline burner is used, which is fed from a small supply tank located five or six feet above the burner.

During the admission stroke, the hot tube is filled with the non-combustible gases remaining from the previous explosion, therefore, the fresh entering gases cannot come into contact with the hot walls of the tube and cause a premature explosion, before the charge is compressed.

As the compression of the new charge proceeds, the fresh gas is forced farther and farther into the tube and at the highest point of compression it has penetrated far enough to come into contact with the hot portion. At this point the explosion occurs.

The tube being of small bore, does not allow of the burnt gases mingling with the fresh within the tube; the waste gases in the tube acting as a regulating cushion. The distance of travel of the new mixture is proportional to the compression, hence the explosion does not occur until a certain degree of compression is attained.

The length of the tube required for a given engine is a matter of experiment, as is also the location of the heated portion. High compression naturally forces the mixture farther into the tube than low, therefore the flame should come into contact with the tube at a point nearer the outer end with high compression than with a low compression.

Shortening the tube causes advanced ignition, as the mixture reaches the heated portion sooner, or earlier in the stroke, because of the decreased cushioning effect of the residue gases in the tube.

The length of tube and location of maximum heat zone should be so proportioned that combustion will take place at the highest compression. Moving flame to outer end of the tube retards ignition. Moving the flame toward the cylinder advances it.

While the hot tube is the acme of simplicity in construction, it is not the easiest thing to properly adjust, as the adjustment depends on compression, temperature of the tube, and the quality of the mixture. Any of these variables may cause improper firing.

The hot tube is rather an expensive type of ignition with high priced fuel, as the burner consumes a considerable amount of gas, and is burning continuously during the idle strokes as well as during the time of firing.

It is practically impossible to obtain satisfactory results from a hot tube on an engine that regulates its speed by varying the mixture or compression, as engines running on a light load will not have sufficient compression to cause the mixture to come into contact with the hot surface, the engine misfiring on light loads.

The tubes are made of porcelain, nickel steel alloy, or common gas pipe, and are of various diameters and lengths.

All of these materials have their faults. Porcelain being very brittle, is liable to breakage. Gas pipe burns out and corrodes rapidly. Nickel alloy is not liable to breakage, is not so susceptible to corrosion as iron, but is far from being a permanent fixture.

Timing valves are a feature of some systems of hot tube ignition, which correct to a certain extent the irregularity of firing of the plain type of tube.

The timing valve is introduced in the passage connecting the cylinder and tube, and prevents the gas in the cylinder from coming into contact with the heated surface until ignition is desired.

The valve is operated by means of mechanism connecting it with the crank shaft. It is evident that with sufficient compression in the cylinder, the time of ignition can be obtained with certainty.

This mechanism is rather complicated, and subject to wear, and the advantage gained by the fixed point of ignition is offset by mechanical complication and consequent trouble.

The action of hot tube igniters is erratic and their use is not advisable unless under unusual conditions. The open flame used in heating the tube is a constant menace, as it is surrounded by inflammable vapors. This feature alone condemns it in the eyes of the insurance underwriters; in many places the use of the hot tube is prohibited both by the underwriters and city ordinances.

The above inherent defects of hot tubes are supplemented by breakage, “blowing,” and clogging of the tube or passage with soot and products of corrosion, each factor of which will cause misfiring.

In case of misfiring, after determining that the tube is not broken or clogged with soot or dirt, see that the engine is being supplied with the proper mixture; that you are obtaining the proper compression; and that the Bunsen burner is delivering a bright blue flame on the tube at the proper point. Never allow the burner to develop a yellow sooty flame. A yellow flame indicates that insufficient air is being admitted to the burner. Remember that an overheated tube is quickly destroyed, and will cause misfiring as surely as an underheated tube. Regulate the gas supply to the burner.

A small leak near the outer end of the tube will destroy the cushioning effect of the burnt gas, and hence will cause premature firing of the charge. Procure a new tube.

Many engines are provided with a sliding burner and chimney which allows of some adjustment of the flame on the tube. In cases of persistent misfiring, move the chimney one way or the other. It may improve the ignition.

(78) Electrical Ignition.

Ignition by means of an electric spark is by far the most satisfactory method as it makes accurate timing and prompt starting possible. It is the most reliable of all systems and is easily inspected and adjusted by anyone having even a rudimentary idea of electricity or the gas engine. For this reason electric ignition is used on practically all modern engines (with the exception of the Diesel types). The spark is caused by the current jumping an opening or gap in the conducting path of the current, and the ignition of the charge is obtained by placing this cap in the midst of the combustible mixture to which the spark communicates its heat.

The method of producing the spark gap, and the method by which the current is forced to jump the gap, divides the electrical ignition system into two principal classes:

(1) The =MAKE AND BREAK=, or =LOW TENSION= system. (2) The =JUMP SPARK= or =HIGH TENSION= system.

In either system the spark is produced by the electrical friction of the current passing through the high resistance of the gas in the spark gap. The incandescent vapor in the gap formed by this increase of temperatures causes the flash that is known as the spark. The temperature of the gap depends principally upon the current flowing through it, the amount of heat developed being proportional to the square of the current.

There is of course a practical limit to the amount of current used in the ignition apparatus to produce spark heat. The limit is generally set by considerations of the life of the battery furnishing the current, expense of generating the current, and the life of the contact points between which the spark occurs.

The heat developed by an electric current is proportional to the amount of resistance offered to its flow and the strength of the current employed. The greater the resistance, the more heat developed.

The resistance of copper wire (the usual conducting path), being very low causes little rise in temperature, but the air in the opening or break has a resistance of many thousands of times the resistance of the copper; hence the current passing across the opening spark or gap raises the air to an exceedingly high temperature.

With a comparatively heavy current flowing across the break, the temperature developed is high enough to boil or vaporize any metal in contact with the spark or flame, rendering the metallic vapors incandescent. With sufficient current, the ends of the wires which constitute the break may be melted away.

For the successful and continuous operation of the engine it is imperative that ends of the conducting path or terminals be made of a metal of a high fusing point in order to withstand the heat of the spark and also that the current be kept to as low a value as possible.

In actual construction the spark gap terminals are generally made of platinum or platino-iridium, or an alloy of high fusing point. Iron is sometimes used, but deteriorates rapidly. Nickel steel lasts longer than common iron or steel but is not as durable as platinum or its alloys.

As the temperature of the electric spark or arc is approximately 7,500° F., and the ignition temperature of an ordinary rich gas at 70 lbs. compression is 1,100° F., it is evident that the quantity of current for ignition may be kept to an exceedingly low value. High compression increases the resistance of the spark gap, and requires higher electrical pressure to force a given current across a gap of given length.

(79) Sources of Current.

The electric current that causes the ignition spark is usually generated or supplied by one of the three following methods:—

1. By the primary battery which converts the chemical energy of metal, and some corroding fluid, into electrical energy, by chemical means.

2. By the magneto or dynamo that converts mechanical work or energy into electrical energy through the method of magnetic induction.

3. By the storage or secondary battery which acts as a reservoir or storage tank for current that has been generated by either of the two above methods. A storage battery simply returns electrical energy that has been expended on it by an external generator. A storage battery does not really generate electricity but as it is often used as a source of current for an ignition system, we will consider it as a generator.

Current producers that convert chemical or mechanical energy into electrical energy are called primary generators, and are represented by the primary battery and dynamo. The above methods are used for generating current for either the high or low tension systems.

Electricity may also be produced by friction, but as such current is without heat value it is not used for ignition purposes. Electricity produced by friction is called static electricity.

Primary and storage batteries always deliver a direct or continuous current of electricity, that is a current which flows continually in one direction. Dynamos are usually made to furnish a direct current, but can be built to deliver either direct or alternating.

Alternating current, unlike the continuous current, changes the direction of its flow periodically; flowing first in one direction and then in the other, the flow alternating in equal periods of time.

Magnetos being a special form of dynamo can furnish either class of current, but with few exceptions are built for generating alternating current.

Either current may be used for ignition purposes for either high or low tension systems.

Alternating current has several advantages not possessed by the continuous current, when used for ignition purposes. The principal advantages are:

1. Alternating current does not transfer the electrode metal of contact points, and consequently causes less trouble with vibrators and “make” and “break” ignitors.

2. Magnetos generating alternating current are less complicated, have fewer parts to get out of order, and are cheaper to keep in repair.

3. Alternating current is not liable to burn out spark coils or overheat with an excessive voltage.

4. Alternating current generators can be used at any speed without the use of governors.

When installing an ignition system give due consideration to the reliability of the source of current. The gas engine is no more reliable than its source of current. Failure of the current means the failure of the engine.

(80) Primary Batteries.

Current is produced in a primary battery by the chemical action of a fluid known as an =ELECTROLYTE= upon two dissimilar metals or solids known as the electrodes. One of the electrodes, the negative, is usually made of zinc which is more readily attacked by the electrolyte than the positive electrode. As the metal of the negative electrode is dissolved and passes into the solution during the process of current generation, the electrolyte is also exhausted. The production of current is accompanied by the liberation of hydrogen gas from the electrolyte from which it is displaced by the zinc taken into solution.

When the electrodes are immersed in the electrolyte, and the outer ends of the electrodes are connected with a wire, a current will flow from the positive electrode to the negative through the wire, and from the negative to the positive electrode through the fluid. It will be seen that to complete the circuit between the electrodes it is necessary that the current flows through the electrolyte.

Electrical energy is actually generated in the primary battery by the chemical combustion of the negative electrode in the same way that heat energy is developed by the burning of a fuel.

By connecting the binding posts of the electrodes to the two wires of the external circuit, a current will flow through the circuit as long as the electrodes remain undissolved, or until the positive electrode is covered with hydrogen gas bubbles.

The bubbles of gas tend to insulate the positive electrode from the electrolyte or fluid, thus breaking the circuit through the fluid, and stopping the flow of current. This action is known as polarization.

When a battery is polarized, the only remedy is to disconnect it from the circuit and allow it to rest or recuperate. The greater the current drawn from a battery, the more rapid the polarization, and it is evident that if the battery is to be used for long periods, polarization must be eliminated, or the current must be considerably reduced in volume. A battery that delivers a small current has a much greater capacity in ampere hours than a battery that has a higher rate of discharge. The greater the discharge rate the longer must be the rest periods.

A battery that is designed for continuous service, or for delivering heavy currents of long duration, is called a closed-circuit battery. Polarization is eliminated in closed circuit batteries by various methods, the usual methods being to place some substance in the electrolyte that will destroy the hydrogen film; or by packing some solid oxidizing material around the positive electrode that will absorb the hydrogen; or by making the positive electrode of some material that will destroy the hydrogen as soon as it is developed.

Batteries that are capable of being operated only for short periods, on account of polarization, are called open circuit batteries. Open circuit batteries are cheaper and more simple than closed circuit batteries. For ignition purposes, a battery is made that is a compromise between the closed and open circuit cells, this being a battery in which the polarization is only partially suppressed. As the demand for current on an ignition battery is small with comparatively long rests between contacts, the compromise battery answers the purpose and is fairly cheap.

All primary batteries are in reality wet batteries, for the reason that it would be impossible to cause a chemical reaction and a current with a dry electrolyte. The action of dry and wet batteries is identical.

There are many types of wet battery in use for various purposes, but few of them are adapted for gas engine ignition because of a tendency to polarize or because of the cost of maintenance.

All wet batteries are not suitable for portable or automobile engines because of the slopping of the liquid electrolyte and the danger of breaking the containing jars. Their weight and bulk is also a drawback.

If the electrolyte or the electrodes be made of impure material local currents will be generated. These currents decrease the life of the cell without producing any useful current in the ignition circuit. Due to the deteriorating effects of the local currents, batteries standing idle for several months will often be found to be completely discharged and worthless without having done any useful work. In the better grade of cells this loss is reduced to a minimum.

A type of wet battery using a solution of caustic soda for an electrolyte, and having zinc and copper oxide electrodes, is extensively used for stationary ignition purposes, and is the most satisfactory type of wet cell for continuous work with this class of engine. The caustic soda battery is of the =CLOSED= circuit type, and is capable of furnishing a strong uniform current without danger of polarization.

The hydrogen bubbles which cause polarization are oxidized or eliminated by the copper oxide electrode as soon as they are formed. The hydrogen combines with the oxygen of the copper oxide forming water.

The copper oxide is gradually reduced to metallic copper by the reaction with the hydrogen, and in the course of time requires renewal. The copper oxide element is rather expensive and cannot be obtained as readily as the electrodes used in other cells.

It will be noted that both electrodes are consumed in the caustic battery, the consumption of the zinc furnishing the current, and the reducing of the oxide furnishing the chemical energy for depolarizing the cell.

(81) Dry Batteries.

Dry batteries are by far, the most convenient and economical form of primary battery to use, for there is no fluid to slop and leak, the first cost is low, the output is large for the weight, and last but not least, the cell can be thrown away when exhausted without great monetary loss. This does away with the expense and annoyance of changing wet cells, a factor that will be appreciated by those that are far from a source of chemical supplies. Since the advent of the automobile the use of dry cells has extended so that they may be obtained in almost any country town or village.

While the cell is not dry, strictly speaking, the solution is held in such a way that it cannot slop around in the cell nor leak out of the seal. The only fault of a dry cell is its tendency to deteriorate with age because of the constant contact of the electrolyte with the electrodes.

The negative electrode of the dry cell (zinc) is in the form of a cup which serves as a containing vessel for the electrolyte and the depolarizer.

The electrolyte is usually composed of a solution of ammonium chloride, with a small percentage of zinc sulphate, this fluid being held by some absorbent material such as blotting paper, or paper pulp.

The electrolyte is applied to the electrodes by means of the saturated blotting paper, which is also used to line the zinc container, thus providing insulation between the electrodes.

A rod of solid carbon which forms the positive electrode is placed in the center of the container, and the space between the rod and the zinc is packed solidly with granulated carbon, the blotting paper lining preventing contact of the zinc with the carbon.

Pulverized manganese dioxide is mixed with the granulated carbon for a depolarizer.

After the zinc container is filled with the electrolyte and pulverized carbon, the top of the container is closed hermetically by means of sealing wax. Granulated carbon is used for it presents a large surface to the electrolyte, reduces the internal resistance of the cell, and therefore increases the current output of the battery.

As soon as the battery starts generating current, polarization begins, with the liberation of hydrogen gas. If the cell is discharged at a high rate, the manganese dioxide will be unable to absorb all of the gas, and consequently pressure will be erected within the cell. The greater the rate of discharge, the greater will be the amount of hydrogen set free, and the higher the pressure.

If a short circuit exists for any length of time, the pressure of the excess hydrogen will speedily ruin it, as the cell will puff up, or even burst under the pressure. If the rate of discharge be kept so low that all of the gas will be absorbed by the manganese, as soon as generated, the cell will furnish a steady current until the elements of the cell or the electrolyte are exhausted.

The steady current limit, or non-polarizing limit is about one-half ampere and if long life of the cell is expected, the current drain should be less than this amount. A good spark coil will develop a satisfactory spark on a quarter to one-half ampere, so that the demand of a good coil is well within the safe limits of battery capacity. The voltage of the average dry cell when in good condition is 1.5 volts on open circuit. When the cell is old or exhausted, the voltage falls rapidly when any demand for current is made on the cell, and the voltage also varies with the rate of current flow, the voltage decreasing with an increase of current.

As there is not much difference in voltage between a new and old cell when on open circuit, it will be seen that the ammeter giving the current output will give a more accurate determination of the condition of the battery. The voltage is independent of the size of cell.

The battery showing the greatest amperage is not necessarily the best for general use, as cells having an unusually high current capacity are generally short lived. The strong electrolyte used in high ampere batteries causes them to burn out or deteriorate rapidly when not in use.

Under ordinary conditions, a correctly proportioned No. 6 ignition cell should show a current of from fifteen to twenty amperes on short circuit when the cell is new, although higher results may be obtained safely with some makes of cells.

While the voltage is the same for all sizes of batteries, and depends on the material used in the construction, the amperes increase with the size of the cell, and the area of the electrodes.

If a cell does not show more than ten amperes on short circuit, it should be thrown out and another substituted for it, as the cell is liable to go out of commission at any minute when reaching this point of exhaustion.

A small battery testing voltmeter or ammeter should be in the kit of every gas engine operator using a battery for ignition, as the exact condition of a vital part of the power plant can be determined quickly and with accuracy. For dry batteries an ammeter is preferable; for storage batteries a voltmeter must be used.

When buying dry batteries insist on having new, fresh cells, as any battery depreciates in value with age. Never take a cell without testing it, as it is the practice of dealers to work off their old stock on unsuspecting customers. Examine the battery closely for the makers’ dates, and if the battery is several months old, it is probable that the electrolyte is dried up or that the electrodes are wasted through long continued local action. As heat stimulates chemical action in the cell, they should be stored in a cool place to retard the wasting action as much as possible. Under all conditions, the cell should be kept dry, since the moisture that is deposited on the cell forms a closed circuit for the current which soon exhausts the battery. Cold retards chemical action in the cell and consequently reduces the output in zero weather to such an extent that starting is frequently impossible.

Multiple cylinder engines exhaust a battery quicker than those with a single cylinder, as there are more current impulses in a given time and consequently more current is used. A battery may be compared with a bottle that holds a certain quantity of fluid. If the water is allowed to drip out slowly it will last for a long time, but if allowed to flow in a continuous stream will soon be exhausted.

With badly designed or poorly adjusted spark coil, the demand on the batteries is greater than with one that is in proper condition. An engine that runs continuously exhausts a battery faster than one that is run at long intervals. Always open the battery switch when the engine is to be idle for any length of time, as the engine may have stopped with the igniter in contact, allowing the battery to expend its energy uselessly.

Test batteries immediately after a run, as the batteries will recover after standing a while, and will show a fictitious value.

A weak, partially exhausted battery will cause a poor spark that will result in misfiring or a loss of power. It is poor economy to attempt running an engine on a weak battery. An engine may run on a weak battery for a short time, and then gradually decrease in speed until it comes to a full stop. Misfiring is generally in evidence as the engine dies down. In case of an emergency, weak batteries may be made to run an engine of an automobile or boat to its destination, by stopping the engine frequently and allowing the batteries to recuperate during the idle periods. A battery that is temporarily weakened by hard service or by a temporary short circuit will usually revive or partially recover its strength if allowed to “rest” for a short time until the hydrogen is absorbed by the depolarizing material. The life of a dry cell can be extended for a few hours by punching a hole in the sealing wax on the top of the battery, and pouring water, or a solution of water and sal-ammoniac into the cell. This will reduce the internal resistance and increase the current. The batteries will run under these conditions for a short time only, and new cells should be procured at the earliest possible moment. No old cell can be made as good as new by any method. Never drop the cells on the floor nor subject them to hard usage mechanically, for if the active material is loosened, the current output will be reduced. A short circuit through a closed switch with the engine stopped or a loose dangling wire will put the cells beyond repair.

If the binding screw on the carbon electrode does not make good contact with the carbon, tighten it to decrease the resistance. Fasten the connecting wires firmly under the binding screws and keep the connections clean.

In the absence of an ammeter, a rough estimate of the condition of the cell may be made by fastening a short wire tightly in the zinc binding post, and touching the carbon surface lightly and intermittently with the free end of the wire. When contact is made with the free end of the wire, a small puff of smoke will arise and a red spark will be seen if the cell is in good condition.

Sometimes the contact made on the carbon will produce only a small black ring on the surface of the electrode. This indicates a battery that is nearly exhausted, and one which is good for only a few more hours of service.

When a number of cells are connected together in such a way that they collectively form a single source of current, the group is called a battery, and the resulting voltage and amperes of the group depends on the way in which the cells are interconnected.

It is possible to connect the cells of a battery in such a way that total voltage of the group or battery is equal to the sum of the voltages of the individual cells. A battery connected in this manner is said to be connected in series. While the voltage of a battery is increased, by series connection, the number of amperes is the same as that given by a single cell, the same current flowing through the set.

(82) Series and Multiple Connections.

Fig. 86 shows the cells connected in series, the carbon terminal of one cell being connected to the zinc terminal of the second. The carbon of the second cell is connected to the zinc of the third, and so on throughout the series, the two remaining terminals of the battery being connected with the ignition circuit. The number of watts or power developed by the group is equal to the sum of the outputs of the separate cells. If the voltage of each cell shown in diagram is 1.5 volts, the total voltage of the group of five cells will be 1.5 × 5 = 7.5 volts, and if the current of a single cell is 15 amperes, the current output of the group will be 15 amperes, or the same as that of a single cell. Almost all ignition apparatus now on the market requires six volts for its operation, so with cells having a voltage of 1.5 volts such apparatus would call for four cells in series, as 6 ÷ 1.5 = 4.

Owing to the increase of internal resistance caused by series connections it is usual to add one more cell than is theoretically required, making a group of five cells to supply the six volts required. A large number of cells will give a hotter spark than a smaller, but the excessive current causes the contact points of the igniter or vibrator to burn off rapidly and also hastens the destruction of the cells themselves.

Batteries connected in such a way that the total amperes of the group is increased without increased voltage are said to be connected in multiple or parallel. When batteries are connected in multiple, the total current in amperes is equal to the sum of the amperes delivered by the separate cells; and, while the current in amperes is increased by multiple connection, the voltage of the group remains equal to that of a single cell.

If each cell connected in multiple has an electromotive force of 1.5 volts, and can deliver 15 amperes, the total current delivered by this system of connection will be 15 × 5 = 75 amperes with five cells, and the electromotive force will be 1.5 volts as in the case of the single cell. By connecting batteries in multiple, the resistance is reduced, allowing a maximum flow of current. The demand on the individual cells is reduced by multiple connection, as each cell only furnishes a small part of the total current. The greater the number of cells, the less will be the current required per cell, with a given total current. As the life of a battery depends entirely upon the rate at which it is discharged, it is necessary, for economical reasons, to keep the current per cell as small as possible, therefore the multiple system would prove of value as it reduces the load to the smallest possible limit. Enough cells should be placed in multiple to reduce the current to less than a quarter of an ampere per cell. The cells shown will not have sufficient voltage to operate ordinary ignition apparatus requiring a potential of six volts, hence the multiple system must be modified in order to have an increased voltage, and at the same time secure the advantages of multiple connections.

(83) Multiple-Series Connections.

A compromise is affected by the multiple series system of connections in which are combined the advantages of both the series and multiple systems of connection.

This arrangement allows sufficient voltage to operate 6 volt apparatus and at the same time reduces the rate of discharge on the individual cells. The series-multiple battery shown in the diagram 88 consists of four groups of batteries connected in multiple, each group of which consists of five cells that are connected in series. The current and voltage in the various branches is shown in the diagram. The series-multiple system is adapted for use with multiple cylinder engines, as engines with more than one cylinder cause a severe drain on the ignition system. Arranging the series groups in parallel increases the life and efficiency of the cells. If an efficient coil is used, the drain of a single cylinder is not too great to be met with a single set of series cells. If possible the set should be provided with a duplicate, so that the load could be transferred from one set to the other at proper intervals by means of a double throw switch.

With a single set of batteries in series the working life of the cells will be approximately twenty hours under ordinary conditions. With four groups of four cells in series, the life of the cell will be approximately 160 hours, or eight times the life of the single set under similar conditions.

While the cost of the cells will be only four times that of the single set, it will be seen that the cost of battery upkeep is halved by reducing the demand on the cells.

Sometimes duplicate sets of series multiple connected batteries are used for heavy duty engines, the engine running on one set for a while and then on the other, allowing the first set to thoroughly recuperate before it is again thrown in service, by means of the double throw switch.

When batteries are multiple or series-multiple connected they should be of the same size and make and of the same voltage. If the cells are of different voltages useless local currents will circulate among the cross-connections, shortening the life of the battery and reducing the output.

In connecting a dry cell use a good grade of rubber insulated wire, preferably wire with a stranded conductor, as it is less liable to break or loosen at the binding screw of the battery. Carefully remove the insulation from the end of the wire that is to be fastened under the binding screw of the battery. Scrape it until it is bright and perfectly free from dirt before fastening it in the battery terminal. Never allow a dirty or corroded connection or a loose wire to exist. An open battery circuit or loose connection will stop engine suddenly, or will prevent starting.

The battery connections should be screwed down tight with the pliers, care being taken that the screws are not broken by the tightening process. See that frayed ends of the wire do not project beyond the binding screw to which they are connected and make contact with other cells or metal objects. Be sure that no insulation gets between the contact braces of the binding screw.

(84) Operation of Dry Cells.

The following hints should be observed to obtain the best results with dry cells.

(1) Never remove the paper jackets from the cells.

(2) Never lay tools or other metallic objects on top of the cells for this will cause a “short” that will quickly exhaust them.

(3) Do not connect old and new cells together, especially with the multiple-series system of connections, for the old cells will limit the output of the new, or else will cause cross-currents that will exhaust all of them.

(4) When trouble develops in the battery, test each cell separately and remove the faulty cells. Do not reject all of the battery because of one or two dead cells.

(5) Place the cells in a wooden box that will protect them from dirt or moisture, and if possible divide the box off into pigeon holes with a cell in each hole. For the best protection against moisture, the box should be boiled in paraffine.

(6) Provide a battery switch on the box that will cut both leads from the cells completely out of circuit when the engine is stopped.

(7) Never place a dry cell in a box that has contained storage cells unless the box has been thoroughly washed out, for the residual acid of the battery will destroy the zinc elements.

(8) Make all connections firmly with well insulated wire and take care that the wire does not make contact with any part of the battery except that to which it is connected.

(9) Keep the battery dry.

(85) Storage Batteries.

The purpose of the storage battery is to store or accumulate the current generated by a dynamo until so that the current will be available when the dynamo is not running. A storage cell does not “store” current in the same way that water is held in a tank, but returns the energy expended on it through the chemical changes caused in the cell by the current.

When the charging current passes through the storage battery chemical changes are produced in the electrodes and electrolyte, and the energy expended on the cell is in the form of latent chemical energy, in which state it remains until the electrodes are connected with one another by a wire or some other conducting medium. When the electrodes are connected through an external circuit, the electrolyte acts on the electrodes causing them to assume their original composition. As they pass into their previous chemical condition the latent chemical energy is converted into electrical energy. The current thus produced may be used in the same way as in a primary cell.

When discharging, the action of a storage battery is similar to that of a primary battery, the current being produced by the action of a fluid on two dissimilar electrodes. Instead of supplying new elements when the battery is discharged, as in the case of the primary cell, the elements are brought back to their original state by passing a current through the cell in the opposite direction to that of the discharge.

There are several combinations of materials which may be used in the making of storage battery electrodes and electrolytes, but with the exception of the lead sulphuric battery and the new Edison battery none have proven a commercial success.

The most common type of storage or secondary cell is the lead-sulphuric type in which the electrolyte is dilute sulphuric acid and the electrodes are lead plates, covered with a chemical composition known as the active material. These plates usually consist of a lead grid, or lattice frame in the pockets of which is pasted the active material. The pockets or lattice bars of the plates are for the purpose of supporting the active material which is of a weak and spongy nature. The active material on the positive plate is usually litharge, while that on the negative plate is red lead.

After charging, the active material on the positive plate is changed to lead peroxide by the action of the current, and the active material on the negative plate is changed into spongy metallic peroxide. The composition of the active material on the plates determines the direction of flow of the discharge, or secondary current. The current flows from the positive plate to the negative through the external circuit.

When fully charged, and in good condition, the positive and negative plates may be readily distinguished by their colors, the positive plate being a dark brown or chocolate color, and the negative a slate or grey color.

The positive active material is hard, while the negative may be easily cut into by the finger nail. The density of the material changes slightly with the charge, as the material expands during the discharge.

The problem of holding the active material securely to the plates during expansion and contraction has been a hard one to solve, each manufacturer having some favorite form of grid or material plug to which he pins his faith. While great improvements have been made in this direction, it is certain that we have not yet reached perfection. Loose active material will cause short circuits and will reduce the output of the cell; loose active material frequently ruins a cell.

The current capacity of a storage battery depends on the area of the plates or electrodes, and in order to increase the capacity of a battery, and consequently the area, it is usual to use a number of plates connected in parallel. A number of small plates of a given area are to be preferred to two large plates of the same area, as the battery will be of a more convenient size.

Customarily there is one more negative plate than positive, so that the extreme end plates in a cell are negative, as the positive and negative plates alternate with each other when assembled.

An ignition battery usually consists of two negative plates and one positive. Cells used for power purposes have as high as sixty plates.

A single cell of storage battery should show about two volts when fairly well charged. If more than two volts are desired more cells should be connected in series. The total voltage will be equal to the number of cells, in series, multiplied by the voltage per cell. The voltage per cell should never be allowed to drop below 1.7 volts, as the cell is likely to be destroyed when operated with a low voltage. Recharge as soon as the voltage drops to 1.8 volts.

The ordinary six volt ignition battery consists of three separate cells connected in series, which are encased in one protecting box.

The plates are prevented from touching each other within the cell by means of a perforated sheet of hard rubber that is inserted in the space between the plates. The perforations allow the liquid to circulate between the plates.

The storage battery is furnished as standard equipment with several well known gas engine builders, and its use is advocated by nearly all. When used in connection with a low tension direct current magneto two independent sources of current are at hand, either of which will ignite the engine in an emergency.

With the magneto-storage battery combination, it is possible to obtain a few small lights at any time, whether the engine is running or not, and the engine is always ready to start on the first “over” with the storage battery and a good mixture.

If a magneto is not used, difficulty is sometimes experienced in obtaining a suitable source of charging current, as many localities do not possess direct current plants. Batteries may be charged from the direct current exciter in an alternating current station, or may be charged by an alternating current rectifier such as is used by automobile garages.

The principal objections to the storage cell are: inconvenience of charging; sulphating of cell when standing without a charge; ease with which the cell is ruined by short circuits; the damage caused by the spilling of the electrolyte; and the fact that the cell gives no warning of failing or discharged condition.

Since the composition of the plates depends on the direction in which the current flows through the cell, it is obvious, that an alternating current which periodically changes its direction of flow will first charge the plates and then discharge them alternately. The result of an attempt at charging with alternating current would be that the plates would be in the same or a worse condition in a short space of time than they were at the beginning. In charging a storage cell care should be taken to determine the character of the current, especially when the cell is to be charged from a magneto. When under charge, the cell is connected to the charging circuit in such a way that the current flows backwards through the cell or in a direction opposite to that when the cell is discharging.

(86) Care of the Storage Cell.

The storage battery should never be left in an uncharged condition with the acid electrolyte in the cell, for the solution will quickly attack the uncharged plates and combine with them to form lead sulphate. As lead sulphate has a high electrical resistance and is insoluble in the electrolyte the sulphate coating will reduce the output or if present in excess, ruin the cell. The sulphate appears as a white coating on the surface of the plates. The only remedy for this condition at the hands of the average engine operator is a prolonged charge, or over charge, at a slow rate. There are several chemical processes but they are too complicated for the average man.

As sediment collects on the bottom of the battery jars, and is liable to cause a short circuit, the plates should be held about half an inch from the bottom of the jar. Care should be taken that the cells of the stationary type of battery are kept dry and clean. Do not allow dirt to drop into the solution as it is liable to destroy the cell.

A volt meter should be used to determine the condition of the battery, and should be used frequently. An ammeter should never be used on a storage battery, as it is of very low resistance, and would probably cause a rush of current that would destroy both the battery and the instrument.

Never short circuit a storage battery, even for an instant, as excessive current will cause the plates to buckle, or will loosen the active material on the plates.

The plates are immersed in the electrolyte, which should cover the entire plate or active surface. If the solution does not cover the plate, the capacity of the cell will be reduced. Plates that are partially covered with solution deteriorate rapidly from “sulphating.” This is caused by the air and acid acting on the damp inactive portion of the plate.

Usually the electrolyte consists of a dilute solution of sulphuric acid and water, but in some ignition cells the solution is “solidified” by some substance to about the consistency of table jelly. The object of this thickened solution is to prevent the solution from slopping and leaking when the battery is being transported.

The solution used in a storage battery is exceedingly corrosive in its action, and if spilled on metal or wood will destroy it immediately. Care should be taken in handling the electrolyte.

A cell should never be discharged below 1.7 volts for below this point, the plates are likely sulphate. When the solution is replaced by fresh, or water is added for the purpose of restoring the electrolyte to its original level, use only distilled water, free from metallic salts and suspended matter.

Many people “test” their cells by snapping a wire across the terminals to “see if there is a good spark.” Nothing could be more injurious to the battery, and as this test indicates nothing, the practice should be discontinued. Make all your tests either with a hydrometer or a voltmeter, the latter is preferable in the average case.

The electrolyte is a solution containing approximately 10% of chemically pure sulphuric acid and 90% of distilled water. The specific gravity of the fluid should be from 1,210 to 1,212 in all cases. A standard battery hydrometer should be used by all storage battery users to ascertain the exact density of the solution as the specific gravity is a direct index to the condition of the cell. A gasoline hydrometer is useless for a storage battery.

When mixing the electrolyte it should be placed in a glass or porcelain jar, and the process should never be performed in the battery jar in the presence of the plates. The solution is very active chemically and should not be brought into contact with metallic or organic substances because of the danger of contaminating the fluid. The acid should always be poured into the water in a thin stream while the mixture is being stirred with a glass or porcelain rod. Pouring the water into the acid is likely to produce an explosion and should therefore be carefully avoided.

As the acid heats the water during the mixing the hydrometer reading should not be taken until the heat caused by the first addition of acid has been reduced to that of the room. Taking a reading with a hot solution will give inaccurate results, unless, of course, the reading is reduced to normal by the method described in a previous chapter. When the reading has been taken and found to be correct and the solution has been reduced to the temperature of the room, the electrolyte may be poured into the cell through the filler openings in the top of the cell. Pour into each cell sufficient fluid to cover the plates but avoid filling the cell to the top, or flooding it.

At the end of the charging time given by the maker, withdraw a sample of the electrolyte by means of a syringe and test the specific gravity. This should not be over 1,290 for a fully charged cell, and if the solution exceeds this amount, pure water should be added until the proper point is reached. Always correct the specific gravity in this way every time the battery is charged as evaporation and internal chemical changes cause the density to change from time to time. The voltage of a good storage battery will be about 2.1 volts when fully charged. Overcharging is wasteful and finally destroys the cell, the effects being similar to those caused by excessive discharges, that is, buckled plates and loosened active material. Overcharging a sulphated battery may cure the trouble, a little overcharging at intervals being better than a long continued overcharge.

An increase in the specific gravity of the electrolyte of from 30 to 50 degrees, with a corresponding rise of voltage, shows that the cell is fully charged.

After the charging is completed remove all of the solution spilled on the battery, preferably by washing, and wipe bone dry. If the solution is higher in the air, remove the excess with the syringe.

(87) Make and Break System (Low Tension).

When a circuit carrying a current is opened or broken at any place in its length, an electric spark will occur at the point at which the wires or contacts are separated. This is due to what might be termed the “momentum” of the current which causes it to persist in its course even to the extent of jumping over a short distance of the highly resistant air in the gap. The size and heat of the spark may be increased by placing a coil of copper wire in series with the circuit that has an iron core in the center of the turns. This coil increases the tendency of the current to jump the gap, or in other words increases the momentum of the circuit.

Each separation of the terminals of the circuit causes but a single spark, so that in order to obtain another the terminals must be again brought into contact and the current reestablished in the circuit before the circuit is again opened. Thus the function of the make and break igniter is to alternately make and break the circuit in the presence of the combustible mixture. To obtain the greatest spark and most certain ignition, the contact points should be opened with the greatest possible speed, an action that is accomplished in the actual engine by springs and triggers.

A typical cylindrical make and break coil consisting of an iron wire core surrounded by a coarse copper wire core is shown by Fig. 91. At one end of the coil will be seen the two terminal screws by which it is connected with the circuit. Another make and break coil is shown by Fig. 92, which has the same type of winding, but differs in having the core wire coil extended beyond the winding and heads. By closely examining the cut, the iron wires will be seen in the projecting core tube at the left end of the coil. A flat base is also provided for fastening it to a stationary foundation.

A typical make and break igniter is shown by Fig. 93, together with the usual circuit consisting of a primary coil and battery. In this figure, A and C are the two electrodes provided with platinum contact points N and O respectively. The electrode A is stationary and is insulated from the iron casing K by the insulating washer H, and the insulating bushing or tube I. The electrode C is oscillated intermittently by the engine through its shaft E, and the trigger G, the springs S serving to snap the platinum contact O away from N at the proper moment. This electrode (C) is in electrical connection with the shell K, and the engine frame at all times, and is provided with a brass bushing F for a bearing surface. The outer containing casing K is bolted to the combustion chamber of the engine by the bolts LL, so that the electrodes A and C project into the combustion chamber.

Current from the battery R passes through the coil winding P to the coil terminal U from which it passes from V to the igniter binding post J. From J it flows along the rod D to the stationary electrode A. Since the rod D is surrounded by the insulating washers and tube H, T and I, the current cannot escape directly to the casing K. With the two platinum points N and O in contact, the current flows through C to the shell K from which point it flows back to the battery R through the conducting path V, completing the circuit. The greater portion of the path V consists of the engine frame. When the electrode is moved in the direction of arrow B, the current is opened and a spark occurs at the point of separation M, in contact with the gas in the combustion chamber. The electrode C being connected with the engine frame is said to be “grounded.” If the stationary electrode A were not insulated from the casting K, the current would pass directly from the terminal J back to the battery R without passing through the contact points at all, and consequently no spark would be produced on the separation of the points.

A push rod which is actuated by a cam on the engine, engages with the trigger G, and causes the spark to occur when the piston is on the end of the compression stroke. In nearly all engines, the relation between the time of the spark and the piston position can be regulated to suit the requirements for advance and retard. This adjustment is necessary in order that the spark may be varied to meet the difference between the starting and running requirements.

While the ignition should be considerably advanced while running, it is necessary to retard it when starting, as the engine is liable to “kick back” with an advanced spark.

This advance and retard device should be accessible while the engine is running, and the operator should be able to control the point of ignition at all times. Many men have been seriously injured by the lack of this device or by neglecting to use it.

The contact points make contact only for a short time before the spark is required in order to reduce the amount of current to the minimum, and therefore increase the life of the batteries.

The duration of the “make” or contact should be as short as possible. Prolonged contact weakens the batteries and causes them to run down rapidly. For the same reason the electrodes should remain separated until the make is actually required.

A certain period of contact is necessary, however, to allow the spark coil to “build up,” but with a properly designed coil the time required is very short.

Some engines provide a device that cuts out the ignition current altogether during the idle strokes. This adds materially to the life of the batteries.

The igniter should be located near the inlet valve, as the cold incoming gases tend to keep it cool and clean, besides insuring the presence of combustible gas around the igniter electrodes. Improper placing of the igniter will greatly reduce the efficiency of the engine. Avoid placing the igniter in a pocket, or in the path of the exhaust gases.

The make and break ignition system has many good features, but cannot successfully be applied to engines running over 500 revolutions per minute, nor can it be applied to engines of less than 3 H. P. as the parts would be too small and delicate to be durable.

The make and break igniter produces the largest and “hottest” spark of any type of ignition, and is especially desirable for large or slow running engines. Being operated at a low voltage, it is not as easily affected by moisture, poor insulation, or dirt as the high tension or jump spark system, nor is it liable to give the operator such a violent “shock.”

Engines governing by the “hit and miss” system have a device that cuts out the current during the “missed” power strokes. This effects a considerable saving in battery current, especially on light loads when the engine misses a great number of strokes.

While possessing many points of merit, the make and break system is open to several serious objections:

1. Due to the high combustion temperature there is excessive wear of the working parts in the cylinder, this wear causes a change in the ignition timing.

2. The low voltage used in the make and break system calls for perfect contact of the electrodes in the cylinder. This contact is often interfered with or entirely prevented by the accumulation of carbonized oil and soot deposited on the surfaces.

3. The wear of the operating spindle or shaft, which passes through the cylinder wall causes leakage, which in turn causes a loss of compression in the cylinder.

4. The wear of the external operating mechanism produces a change in the timing. The edge of the fingers, wiper blades, etc., tend to cause an advance in the ignition as a general rule, with the attendant danger of broken crank shafts.

5. The system is mechanically complicated, correct operation calling for constant care as to adjustment.

All ignition apparatus wears in the course of time and changes the timing of the engine. The electrodes and push-rods wear and require readjustment. Generally the tendency of worn parts is to advance the ignition. This change in timing occurs so gradually that the operator does not notice it until the engine begins to pound, or until the efficiency has been considerably reduced.

When the engine is new it is well to mark the ignition mechanism in such a way that the relative positions of the crank and igniter will be shown at the time when the igniter trips. It will then be possible for the operator to refer to the marks at any time to tell whether his ignition is occurring at the proper time. Always mark the half-time gears when taking the engine apart for the difference of one tooth when reassembling will be sufficient to throw the engine out of time.

The usual method of marking the gears, is to center punch, or scratch one tooth on the small gear, and then mark the two teeth of the large gear that lie on either side of it. With these marks it is possible to replace the gears in their original and proper positions.

The igniter should trip, causing the electrodes to separate just before the end of the compression stroke is reached, or just before the crank reaches the inner dead center. The distance lacking the exact dead center represents the instant of time between the time of ignition and the actual pressure established by the combustion.

As most engines have the ignition considerably retarded when starting, the igniter will trip later with the lever in the “start” position than when in the “running” position. Never fail to retard spark when starting nor forget to advance it when engine is up to speed.

The actual advance given to an engine depends on the character of the fuel and on the speed.

An engine is said to have an advance of 10°, if the crank lacks 10° of having made the inner dead center at the time of ignition.

The most economical point of ignition is easily determined when the engine is running on a steady load, by varying the point of ignition and noting the position assumed by the governor.

(88) Operation of the Make and Break Igniter.

To keep the igniter in order, and to obtain the best results with the least trouble, the following hints should be observed:

(1) Clean the igniter frequently, and remove all deposits of oil and carbon. For cleaning, the igniter must be removed from the cylinder, care being taken to avoid injury to the packing or gasket. Graphite dusted on the gasket will prevent it from sticking to either the igniter or cylinder.

(2) If the contact points are rough, pitted, or covered with a carbon deposit, the scale should be removed, and the points smoothed down with a fine file, taking care that the two faces are filed parallel with one another.

(3) Insulating washers and tubes should be removed and washed in gasoline. The hole through which the igniter rod passes should be scraped free from any deposit for much trouble can be caused by a tight working shaft.

(4) Examine the hole or bushing through which operating spindle passes, for wear. A worn spindle or bushing may cause a serious loss of compression; replace worn bushing at once.

See that the insulation of the stationary electrode is not broken. If it is injured in the slightest degree, replace it with new.

(5) Often the sparking points may be cleaned temporarily without removing the igniter from the cylinder by pulling upon the outside finger or trigger until the points come together, and then pushing in towards the cylinder several times on the movable electrode, which slides them one on the other, scraping off the deposit. This method is only a make shift.

(6) After removing igniter, replace all wires, screwing them firmly into place. The ends of wires and connecting screws should be perfectly clean when the connection is made; to insure perfect contact, the surfaces should be scraped or sand-papered until bright and shining. See that no foreign matter of any kind gets between the wires and the metal of the binding screws. Wherever possible connections should be soldered.

(7) A small coil of the wire should be made at the point of connection; i. e., the wire should be a trifle longer than necessary to reach the binding screw, the excess wire being coiled up on a pencil. This coil allows of removing igniter, allows for broken wire ends and reduces the tendency to loosen the connection.

(8) Ground wires, or wires connected with the frame of the engine should receive careful attention. They are generally fastened under some screw or bolt on the engine which may become loose or fail to make contact, thus opening the entire circuit and causing the engine to stop. The ground wires are generally connected in inaccessible places, and require all the more attention for this reason.

(9) For the primary of low tension wiring, use only the best grade of stranded rubber covered wire. A special wire for ignition purposes is on the market. It is rather expensive but is just the thing for the service.

Never use cotton covered or waxed wire. This covering affords absolutely no protection against moisture or abrasion.

(10) As the voltage of a primary circuit, or circuit for make and break is very low, and the current comparatively high, it is well to have the copper as large as possible. It should never be less than number 14 gauge. Don’t use solid wire if you can obtain stranded conductor. (Stranded wire is made up of a number of fine wires which are twisted into a cable or rope of the desired size.)

(11) Oil destroys rubber insulation and should be kept off the wiring. Try to locate the conductors so that they will be out of range of oil thrown by the moving parts.

(89) Jump Spark System (High Tension System).

Due to its simplicity and the light weight of its moving parts, the high tension ignition system is applied to practically all small, high speed engines running 500 R.P.M. or over. The high tension system is also desirable from the fact that it has no moving parts in the cylinder of the engine.

The principal objection to the high tension system is the ease with which the high voltage current leaks or short circuits, moisture being fatal to the operation of a jump spark engine.

Instead of producing the spark by breaking the circuit of a low tension current, the spark is produced by increasing the voltage to such a point that the current will jump directly across a fixed gap. To cause the current to jump through the air requires an extremely high voltage, and as the battery current is very low it is necessary to introduce a device known as a “transformer” to stop the current up to the required tension. In addition to the voltage required at atmospheric pressure (about 50,000 volt per inch of spark) we must also furnish sufficient pressure to overcome the increased resistance due to the compression in the cylinder.

Unlike the spark coil used on the low tension make and break system, the induction coil or transformer coil has two separate and distinct coils, that are thoroughly insulated from each other. One coil has a few turns of heavy copper wire which is called the primary. The other consists of many thousands of turns of very fine copper wire, and is called the secondary. Both coils are wound around a bundle of soft iron wire called the core, from which they are carefully insulated. When a battery or magneto current flows through the primary coil, the core is magnetized, and throws its magnetic influence through the turns of the secondary coil.

In Fig. 94 the primary coil and the low tension battery and magneto circuit are represented by heavy lines. The secondary coil, and high tension circuit are represented by light lines.

In order to obtain a continuous discharge of sparks it is necessary to make and break the current in the primary coil very rapidly. This is done by means of the interrupter or vibrator, which is indicated in the diagram by V. The interrupter consists ordinarily of a spring A on which is fastened a soft iron disc D and a platinum contact point B. When the core is magnetized it attracts the iron disc D which is pulled toward the core, bending the spring A and breaking the contact between the platinum point B and C. When the contact points are separated, and the current broken, the core loses its magnetism, and the spring assumes its normal position, which brings the platinum points B and C into contact once more, and reestablishes the current through the primary. The core is again magnetized and the primary current is again broken, and so on. This make and break of the current is thus accomplished automatically, the current being broken many thousands of times per minute, the vibrator moving so fast as to cause a continuous hum.

As soon as the current starts flowing, the magnetic force spreads out through the secondary coil and threads through the turns of which it is composed. The instant that the current ceases, the magnetic force decreases and the turns are again threaded by the magnetic field on its return to the core.

Thus two magnetic waves are sent through the secondary coil, one when the circuit is “made,” and one when the circuit is “broken.”

When a magnetic wave threads or spreads through the turns of a coil of wire, a current of electricity is generated in the coil, the quantity and pressure or voltage of which is proportional to the intensity of the magnetism, and to the number of turns of wire in the secondary coil.

Thus it will be seen that at every make and break of the low tension current in the primary coil, a current is generated in the secondary. As the voltage generated in the secondary is roughly proportional to the number of turns in the secondary, and as there are many thousands of turns, it is evident that the voltage in the secondary will be very high. Thus by the use of the induction coil, the low tension battery current is transformed into a high tension current of sufficient voltage to break down the high resistance of the spark gap.

The condenser is shown at L which has one wire leading to the vibrator spring A, and one wire to the contact screw M. The function of the condenser is to absorb the spark produced at the vibrator points so that the break is made quickly, producing a maximum spark. The intensity of the spark depends upon the quickness with which the primary current is broken, and if it were not for the condenser the length and intensity of the spark would be greatly reduced. This device consists of alternate layers of paper and tin foil, every other leaf of foil being alternately connected to the vibrator spring and to the contact screw.

A method of using two independent sets of battery is shown in the diagram, so that either set may be thrown into circuit by means of the double throw switch O. When handle J is in contact with E, the current of battery set H flows through the coil as shown by the arrows. When J is in contact with F, the battery C is thrown into circuit. The spark gap is shown by X, which represents the spark plug in the cylinder.

In practice, the portion of the circuit shown by I-U is generally formed by the frame of the engine, or is grounded. The terminal P of the high tension circuit is always grounded through the threaded shell of the spark plug, the grounded circuit being shown by the dotted lines. Grounding saves wire and many connections, for with P and U connected to ground it follows that one binding post will serve the place of one high tension and one primary post, making three coil connections instead of four.

In order that the spark will occur in the cylinder of the engine at the proper time, a switch must be placed in the primary circuit of the coil, that will open and close the circuit at proper intervals. Such a switch is called a timer, and is always driven by the engine. The timer is connected to the engine shaft in such a way that contact is made at, or slightly before, the time at which the explosion is required, and as soon as possible after spark occurs the current is cut off.

For multiple cylinder engines it is usual to provide one coil for each cylinder, the primaries of which are controlled by a single timer and battery. A high tension wire from each coil runs to the corresponding cylinder. Instead of having a number of coils with a battery system, there are two or three makes that operate with one coil in combination with a special device known as a distributor which controls the high tension current. The high tension distributor directs the current to the proper cylinder that is in the order of firing, the timing being performed by a timer similar to that used with multiple coils except that a single contact sequent is supplied.

(90) Vibrator Construction.

Since the efficiency of the high tension coil depends largely on the construction and efficiency of the vibrator, the different coil makers have developed various types of vibrators that differ greatly from the simple device shown in the coil diagram in details.

The main objects in view in the construction of a successful vibrator are:

1. To reduce the weight of the moving part as much as possible in order to increase the speed of vibration, and to make the trembler instantly responsive to the timer.

2. To cause the contact points to separate as rapidly as possible in order to cause the maximum spark.

3. To have the contacts as hard and infusible as possible to resist wear and the action of the spark between the contacts.

4. To make any adjustments that may be required, due to wear, as simple and accessible as possible.

The types of vibrators are legion, and we have not the space to go into the details of all the prominent makes, but will illustrate and describe two well known types.

The Kingston vibrator made by the Kokomo Electric Company, is a good example of a modern vibrator and is shown in detail by Fig. 95. All adjustments between the contact points are made by means of the contact screw A which carries a platinum point at its inner end. The retaining spring D keeps the contact screw from being jarred out of place by the engine vibration, without the use of lock nuts. Turning A against the vibrator, the tension of the spring B is increased, raising the screw decreases the tension. Increasing the tension screw increases the length and heat of the spark, and also increases the current consumption. At N is a separate thin iron plate which is acted on by the magnetized core, a rivet fastening the plate to the main vibrator spring is shown at the end of the spring. The current enters through the lug C, and from this point the circuit is the same as shown in the coil diagram.

(91) Operation of the Jump Spark Coil.

The spark produced by a coil in good condition should be blue-white with a small pinkish flame surrounding it, when the gap is ¼ of an inch or less. The sparks should pass in a continuous stream with this length of gap without irregular stopping and starting of the vibrator. Coils giving a sputtering, weak discharge that causes sparks to fly in all directions are broken down and should be remedied.

The secondary windings of coils are often punctured or broken down by operating the coil with the high tension circuit open, or by trying to cause long sparks by increasing the spark gap over ⅜ of an inch in the open air. Coils are also broken down by allowing excessive currents to flow in the primary coil. Never cause a spark to jump over ⅜ of an inch.

High compression in the cylinder shortens the jumping distance of a high tension spark. Coils that will cause a stream of sparks to flow across a gap of ½ an inch in the open air are often unable to cause a single spark to jump a gap of 1/32 of an inch under a compression of 80 pounds per square inch in the cylinder.

Remember that a hot spark causes rapid combustion, and will fire a greater range of mixtures and “leaner” charges, than a straggling, thin, weak spark. Spark coils that give poor results with a long spark gap under high compression are often benefited by the shortening of the spark gap. Shortening the gap will increase the heat of the spark, and will insure the passing of a spark each time that the timer makes contact. A good coil should have no difficulty in igniting a piece of paper inserted between the wires forming the spark gap in the open air.

The adjusting screw affords a means of increasing or decreasing the tension of the vibrator spring, and the amount of battery or magneto current flowing through the primary coil. Increasing the tension of the spring requires stronger magnetization of the core to break the circuit of the contact points. This in turn calls for more current from the battery; hence in order to lessen the demand for current on the battery, the tension should be as little as possible to obtain the necessary spark. An increased tension produces more spark as the magnetization of the core is increased, but for the sake of your batteries decrease the tension as much as possible with a satisfactory spark.

Almost all operators have a tendency to run with too stiff a vibrator, and hence use too much current. An efficient coil should develop a satisfactory spark with ¼ to ½ of an ampere of current in the primary coil. I have often found coils that would work well with ½ ampere, that were screwed up so tight that the coils were consuming 4 to 5 amperes or 8 to 10 times as much as they should.

A battery ammeter used for testing the current consumed by coil will save its cost many times over in batteries and burnt points if used at frequent intervals in the primary circuit.

An automobile or marine engine should be tested for vibrator adjustment in the following way:

Adjust vibrator so that spring is rather stiff. Start engine and get it thoroughly warmed up and running at full speed, then slowly and gradually decrease the tension of the spring until misfiring starts in; then slowly increase tension until misfiring stops. Increase the tension no farther; this is the correct adjustment.

Poor vibrator adjustment is the cause of much trouble and expense as it uses up the batteries and wastes fuel. The principles of correct adjustment are simple, the adjustment easily made, and there is no possible excuse for the high current consumption and rapid battery deterioration met in every day practice. The usual practice of the average operator is to tighten the vibrator until the spark (observed in the open air) is at its maximum. This is commonly known as “adjusting the coil;” shortly after you hear of him throwing out his batteries as no good. After once getting the vibrator in proper trim the ear will give much information as to the adjustment.

A vibrator adjusted too lightly will cause “skipping” or misfiring with the consequent loss of power.

Never attempt to operate a coil that is damp; the coil will be ruined beyond repair. Above all, do not place the coil in a hot oven to dry, as the box is filled with wax, and if this is melted it will run out and reduce the insulation of the coil. Dry coil gradually.

If the batteries are new or too strong the vibrator may be held against the core of the coil so that the vibrator will not buzz. If this is the case loosen the screw until it works at the proper speed. If the batteries are weak, the coil may not be magnetized sufficiently to draw the vibrator and break the circuit. If this is the case tighten the screw. If the vibrator refuses to work with the battery and wiring in good condition, and if you are sure that the current reaches the coil, look for dirty or pitted contacts on the vibrator.

Should the contact points be dirty, clean them thoroughly by scraping with a knife or sandpaper. Water on the points will stop the vibrator, as will oil or grease.

If contact points are of a uniform gray color on their contact surfaces, and are smooth and flat without holes, pits or raised points, they are in good condition. If pits, discolorations or projections are noted, the contact surfaces should be brought to a square, even bearing by means of a small, fine file. The point should not come into contact on an edge, but should bear on each other over their entire surface. Do not use sand paper to remove pitting, as it is almost impossible to secure an even, flat surface by this means.

It is best to remove the contact screw and vibrator blade for examination and cleaning, as it is much easier to file the points square and straight when removed from the coil.

Be careful not to bend the vibrator spring when cleaning, as the adjustment will be impaired. When replacing contact screw and vibrator blade in coil, be careful that they are in exactly the same relative position as they were before removing. Also be sure that the contacts meet and bear uniformly on their surfaces.

(92) Primary Timer.

The duty of the primary timer is to close the primary circuit of the spark coil at, or a little before the time at which the explosive of the charge is required. The exact time at which the timer closes the circuit depends on the load, the speed, and the nature of the fuel. The lapse of time between the instant that the timer closes the circuit and the instant at which the piston reaches the end of the compression stroke is called the “advance” of the timer. When the timer closes the circuit after the piston reaches the end of the stroke, the timer is said to be “retarded.” The timer is constructed so that the time of ignition or the advance and retard can be varied between wide limits. Advancing the spark too far will cause hammering and power loss as the piston will work against the pressure of the explosion.

Retarding the spark will cause a loss of power, as the compression will be less when the piston starts on the outward stroke; and also for the reason that more of the heat will be given up to the cylinder walls as the combustion will be slower. The pressure in the cylinder is less with retarded ignition. Greatly retarded ignition often causes overheating of the cylinder walls, especially with air cooled engines, and also overheats and destroys the seat and valve stem of the exhaust valve. Do not expect the engine to develop its rated horse-power or run efficiently with a late, or retarded spark.

When the engine is installed, and before the timer wears or has a chance to get out of adjustment, look it over carefully and see whether the maker has left any marks relating to the timing of the spark. If there are no marks, it is well to determine the relation between the position of the piston and the timer, as the efficiency of the engine depends to a great degree upon the firing point.

Timers are advanced and retarded by partially rotating the housing either in one direction or the other. When the timer is mounted directly on the cam shaft with the cam shaft traveling in a direction opposite to that of the crank shaft, the timer will be retarded by moving it in the same direction as the cam shaft travels, moving it against cam shaft rotation advances the spark.

Timers for two stroke cycle engines rotate at crank shaft speed, and the direction of advance and retard varies with the methods adopted for driving the timer.

(93) Timer Construction.

Fig. 97 shows a typical timer and circuit arranged for a four cylinder engine. The device can be arranged for any number of cylinders, however, by changing the number of sectors, the sectors being equal to the number of cylinders. There are timers on the market that differ from the one shown in the diagram but the principle of operation is the same with all. The shaft E is usually connected to the cam shaft and is electrically grounded to the engine frame at L by means of the bearing in which the shaft rotates.

The lever F mounted on the shaft E carries the pivoted arm H which is free to move on the pivot to a limited extent to allow for wear on the walls W-W-W-W. At one extremity of H is the roller I which rotates on the pin J, as the roller runs around W-W-W-W. At the other extremity of H is fastened the spring S, which forces I into contact with the walls. A-B-C-D are metallic contact sectors whose connections lead to the four spark coils.

When the metal roller I comes into contact with one of the sectors as at B, the sector is grounded to the engine frame by the roller, the current traveling through the roller and its pin, through lever H and its pin, through the lever F and shaft E to ground at L, the course of the current being indicated by the arrows.

As the shaft E rotates and carries with it roller I, the roller makes contact with the sectors in order B-C-D-A, if rotated in the direction shown by arrow, which rotation grounds the primary coils of the spark coils R^3-R^4-R^1-R^2 in succession; the connection from the timer to the primary being to the primary binding posts P^3-P^4-P^1-P^2. A high tension spark occurs at each contact of the roller with the sectors, as the contact allows current to flow through the primary of the coils. The high tension binding posts S^1-S^2-S^3-S^4 are connected with the spark plugs or spark gaps U^1-U^2-U^3-U^4 by means of high tension cables. As soon as the timer grounds a coil, the coil produces a high tension spark in its corresponding spark plug.

It is evident from the foregoing that the timer not only determines the time at which a spark will take place, but it also determines the cylinder in which the spark will be produced, providing of course that a spark coil is provided for each cylinder.

The contact sectors A-B-C-D are insulated from each other by the insulating walls W-W-W-W, the inner surface of which provides a path on which the contact roller I revolves.

The contact sectors and insulating walls are encased by the protective housing Z, to which they are rigidly fastened.

The housing Z can be moved back and forth on the shaft E for advance and retard, by means of the lever K.

The current flows from the battery terminal V (with the roller in the position shown) through the switch M, through coil R^3, post P^3 to sector B, from which it passes through the roller I, levers H and F to ground. From the ground on the engine frame the current flows back to its source, the battery O, thus completing the circuit. When the roller makes contact with sector C, the coil R^4 is energized, contact with D energizes R^1, and so on. No two coils can be thrown on simultaneously as only one coil is grounded at a time. The high tension current flows from each coil to its plug as soon as the current passes through the primary of that coil.

In some timers, the current is taken from the revolving arm through a separate connection to ground instead of grounding the shaft through the bearings. With these timers, the connection is not affected by worn bearings or an oil film that tends to insulate the shaft from the bearings.

(94) Operation of Timers.

Timers frequently cause misfiring which is generally due to dirt or oil getting between the contacts, or to the wear of the insulating walls W-W-W-W, or to the wear of the moving parts.

Dirt or gummy oil will prevent the contact coming together and completing the circuit, or will clog up the rollers or levers so that they cannot perform their functions properly. This will of course interfere with production of the spark.

The contacts and moving parts of the timer should be kept as clean as possible, all dirt and heavy oil being removed by means of gasoline at regular periods. Make a practice of cleaning out the timer at intervals not greater than one month; oftener if possible.

Parts subject to wear, such as the roller pin J and the bearings should be well lubricated, none but the lightest oil being employed for this purpose. Heavy grease will gum the contacts and cause trouble. There should be no rough places or shoulders on the contact sectors or on the walls W-W-W-W as roughness will cause the roller to jump over the high places which in turn result in misfiring. The remedy is to machine the surfaces of the sectors and walls by grinding or turning in the lathe. Care should be taken in this operation to have the interior perfectly smooth and the sectors perfectly flush with the walls. Repair black or burnt sectors immediately by grinding or sand paper.

Burnt spots or blackened surface on the contact sectors prevent good contact between roller and sector, sectors should show a bright, shining metallic surface.

Sometimes the insulation warps or swells above the contacts so that the roller jumps over the contacts without touching them, or if for any reason that contact is made under these conditions, it is of a short period and results in a poor spark.

Timers often make good contact when starting, or at low speed, and misfire badly at high speed. This will be caused generally by the contact sectors or insulation projecting beyond one another, the roller has time to make good contact at low speed but jumps over the sector at high.

The roller I may become rough or develop a flat stop which will cause it to jump over the contact occasionally, or it may become loose on its bearing pin J, causing intermittent misfiring.

The wearing or loosening of pins J and X result in poor contact. Should pin J fall out of the lever H, the roller would drop out of the fork and cause serious damage. This has happened in two cases to my knowledge.

Should the spring G weaken or break, contact will be made intermittently at high speed, and no contact at low. In this case it would probably be impossible to start the engine. In case the spring breaks, a rubber band may be used temporarily. Wire connections to the timer should be examined frequently as the continual back and forth movement tends to twist and loosen the wire. Use stranded or flexible wire for these connections, if possible.

Before removing the timer mark the hub and the shaft so that the hub can be properly replaced. If this is not done the engine will be out of time with the usual results of hammering or power loss.

Should the gears which drive timer shaft be removed, be sure and mark the teeth of both gears in such a manner that there will be no mistake possible in reassembling them. Mark a tooth on the small gear by scratching or with a center punch (the tooth selected should be in mesh with the large gear). Then mark the two teeth of the large gear that lay on either side of the marked tooth of the small gear. Thus it will be easy to locate the proper relative position of the two gears at any time.

(95) High Tension Spark Plug.

The high tension spark plug is a device that introduces the spark gap and spark into the combustion chamber, and at the same time insulates the current carrying conductor from the cylinder walls. Since the voltage of the jump spark current is very high it is evident that the insulation of the plugs must be of a very high order and that this insulation must be capable of withstanding the high temperature of the combustion chamber. A cross-section of a typical plug is shown by Fig. 98, together with its connections and the course of the current, the latter being shown by the arrow heads.

The electrode B through which the current enters the cylinder is thoroughly insulated from the walls by the porcelain rod C.

The porcelain forms a gas tight joint with the threaded metal bushing F at the point P, the tension caused by the electrode B and the nut I holds the porcelain firmly on its seat at P.

The nut is supported by the porcelain shell H which rests in the top of the metal bushing F. A washer L is inserted between H and F to insure against the leakage of gas from the plug should a leak develop at P. L being a soft washer (usually asbestos) allows the porcelains C and H to expand and contract without breaking. A packing washer or gasket is also placed at the point where the electrode B passes through the porcelain H. This is the washer Q, held in position by the nut I. This washer is elastic and reduces strain on porcelain caused by the expansion.

The cylinder wall G has a threaded opening R into which the plug is screwed, the threads of the opening corresponding with the threads on the metal sleeve E. The plug may be removed from the cylinder for examination without disturbing the adjustment of the electrode and porcelains by unscrewing it at R.

Allowing the current to jump from the electrode to the cylinder wall via the metal sleeve saves one wire and connection, the cylinder and the frame of the engine serving as a return path for the current. This simplifies the wiring and minimizes the danger of high tension short circuits.

By unscrewing the threaded metal bushing F it is possible to examine the condition of the porcelain rod C at the point where it is exposed to the heat of the cylinder. This inspection can be made without disturbing the packed joints at L or Q.

In the high tension, or jump spark system, the spark gap D-K is of fixed length, hence there are no moving parts or contacts within the cylinder to wear, to cause leakage of gas, or to cause a change in the timing. This advantage is offset to some degree by the difficulty experienced in maintaining the insulation of the high tension current.

The high tension current leaves the spark coil M at the binding screw N, flows along the wire J, and enters the spark plug at the binding screw A. From the binding post the current follows the central electrode B to its terminal at D. At D a break in the circuit occurs which is called the spark gap. It is at this point that the spark occurs, the current jumping from D to point K through the air. Point K is fastened in the threaded metal sleeve E which is in turn screwed into the cylinder wall G or ground. From the ground the current returns to its source through binding post O to the coil. The spark therefore occurs inside of the cylinder wall and in contact with the combustible charge, at the point marked “spark” in the cut.

If the fuel, lubricating oil, and air are not supplied in proper proportions, soot will be deposited on the lower surface of the porcelain, and as soot is an excellent conductor of high tension current, the current will follow the soot rather than the high resistance of the spark gap, a condition that will result in misfiring or a complete stoppage of the motor. Carbonized lubricating oil or moisture have the same effect.

Preventing the deposits of soot, moisture and carbonized oil is the chief object of plug manufacturers, many of whom have brought out designs of merit. In fact the problem of elimination of soot is the principal cause of the many types of plugs now on the market.

While many plugs differ in minor refinement of detail from the typical plug shown, the connections and general construction are the same in all types, the spark being produced in a gap of fixed length which is insulated from the cylinder.

A well known form of plug, the Bosch, is shown by Fig. 99 a-b. In this plug a special material known as Steatite is used instead of the usual porcelain. The three external electrodes surrounding the center electrode is a particularly efficient arrangement, especially for magnetos. A peculiar form of pocket minimizes the soot problem.

As porcelain is brittle and is easily broken by the effects of heat or blows, mica insulation is often used in place of the porcelain. The central core of a mica plug is formed by a stack of mica washers, which are held in place by the central electrode and the upper lock nuts.

A poorly constructed mica plug is easily destroyed by a weak, stretching, electrode, or by an overheated cylinder. The latter causing the washers to shrink and admit oil between the layers of mica washers causes a short circuit. As soon as the mica washers loosen and separate, they should be forced together by means of the mica lock nuts on the top of the plug.

If by any reason the mica core becomes saturated with oil, it is best to obtain a new one, as it is almost impossible to remove the oil by simple means open to the average operator.

The chief value of a mica plug lies in its toughness and mechanical strength, a good mica plug being practically indestructible.

When heated, porcelain does not expand at the same rate as the metal sleeves, hence in poorly designed or imperfect plugs, heavy strains are thrown on the delicate porcelains which causes them to crack. When a crack develops it provides a lodging place for soot and carbon which of course causes a short circuit. Should a compression leak occur through faulty packing between the porcelain and sleeve, it should be immediately tightened up for eventually it will leak enough to destroy the plug or reduce the output of the engine.

When ordering a plug be sure that you know the size and type required by your engine. Some engines require a longer plug to reach the combustion chamber than others. Never install a shorter plug than that originally furnished with the engine. Be sure that the plug is not too long as it may interfere with the action of the valves or may be damaged by them. Plugs are furnished with several threads and taps, i. e.:

½ inch pipe thread (Generally used on stationary engines). Metric Thread (Generally used on imported autos). ⅞ inch A. L. A. M. Standard (Used on Domestic automobiles).

Using a plug in a hole tapped with the wrong thread will destroy the thread in the cylinder casting and cause compression leaks.

(96) Care of Spark Plug.

Porcelains are often broken by screwing the plug too tightly in a cold cylinder, as the cylinder expands when heated and crushes the frail plug. A plug installed in this manner is difficult to remove as the expanded walls grip the thread. The plug should be screwed in just enough to prevent the leakage of gas. A short thin wrench should be used in screwing the plug home such as a bicycle wrench. A wrench of this type is so short that it will be almost impossible to exert too much force, and will be thin enough to avoid any possible injury to the packing nut. Bad leaks may be detected by a hissing sound that is in step with the speed of the engine, small leaks may be detected by pouring a few drops of water around the joint. If a leak exists bubbles will pass up through the water and show its location.

Plugs are more easily removed from a cold cylinder than a hot. If the plug sticks when the engine is cold and is impossible to remove with a moderate pressure on the wrench squirt a few drops of kerosene around the threads. Never exert any force on the porcelain or insulation. The high tension cables should be connected to the plugs by means of some type of “Snap Terminal,” such terminals may be had from automobile dealers.

These terminals make a firm contact with the plug and do not jar loose from the plug by the vibration of the engine. They are easily disconnected when the inspection of the plug becomes necessary, and are generally a most desirable attachment.

The high tension cable should be firmly connected to the plug terminal under all circumstances. A loose connection will cause misfiring or will bring the engine to an abrupt halt. If snap terminals are not used the plug binding screw should be screwed down tightly on the wire. When making connections see that the wire is bright and clean, and that frayed ends of the wire do not project beyond the plug and make contact with other parts of the engine.

A large percentage of high tension ignition troubles are due to short circuits in the spark plug which are generally caused by deposits on the surface of the plug insulation. Soot or oil may be removed from the plug by scrubbing the porcelain and the interior of the chamber with gasoline applied by a tooth brush. Examine the plug for cracks, and if any are found, replace the porcelain or throw the plug away. A cracked porcelain is always a cause of trouble.

To test a plug for short circuits, remove it from the cylinder, reconnect the wire, and lay the sleeve of the plug on some bright metal part of the engine in such a way that only the threaded portion is in contact with the metal of the engine. Close the switch and see if sparks pass through the gap. If no sparks appear, and if the coil is operating properly, clean the plug. As an additional test for the condition of the coil, hold the end of the high tension cable about ¼ inch from the metal of the engine while the coil is operating. If a heavy discharge of sparks takes place between the end of the cable and the metal of the engine, the coil is in good condition.

If a partial short circuit exists, the spark at the gap will be weak and without heat; the result will be intermittent, or misfiring with a loss of power. Moisture in the cylinder is a common cause of plug short circuits, the moisture coming from leaks in the water jacket or from the condensation of gases in a cold cylinder. A drop of water may bridge the spark gap, allowing the current to flow from one electrode to the other without causing a spark.

If a cloud of bluish white smoke has been issuing from the exhaust pipe before the misfiring started, you will probably find that the trouble is due to sooted or short circuited plug.

The remedy is to decrease the amount of lubricating oil fed to the cylinder.

When a magneto is used the intense heat of the spark causes minute particles of metal to be torn from the electrodes and deposited on the insulation as a fine metallic dust. This will of course cause a short circuit and must be removed. Short circuits are sometimes caused by the magneto current melting the electrodes and dropping small beads of the metal between the conductors. All metallic particles should be removed from the plug.

While a spark plug may show a fair spark in the open air test, it will not always produce a satisfactory spark in the cylinder on account of the increased resistance of the spark gap due to compression.

Compression increases the resistance of the spark gap enormously and thin, highly resisting carbon films that would cause very little leakage in the open air will entirely short circuit the gap under high pressure, the current taking the easiest path which in the latter case is the carbon deposit.

In order to produce conditions in the open air test similar to those in the cylinder we must devise some method of increasing the resistance of the spark gap in the open air above any possible resistance that could be offered by the carbon film.

Placing a sheet of mica or hard rubber between the electrodes, or in the spark gap, will increase the resistance to the required degree. If the spark plug is in good condition the spark will jump from the insulated terminal to the shell when the mica is in the spark gap, but if a short circuit exists the current will go through it without causing a spark. It is assumed that the battery and coil are in good condition when making the above test.

If the electrodes or spark points are dirty they should be cleaned with fine sand paper, special attention being paid to the surfaces from which the spark issues. When reassembling the plug, see that all of the washers and gaskets are replaced and that the length of the spark gap is unchanged. A little change in the spark gap may make a great change in the spark. A good spark is blue white with a faint reddish flame surrounding it. When the discharge is intermittent or sputters in all directions, either the coil or the plug are partially short circuited. Always have a spare plug on hand.

Ordinarily the length of the gap or the distance between the electrodes should be about 1/32 inch for batteries, and a trifle less for magnetos. A silver dime is a good gauge for the gap. If the engine misfires with the coil and batteries in good condition, try the effects of shortening the gap a trifle, usually this will remedy the difficulty. Exhausted batteries may be made operative temporarily by closing up the plug gap to 1/64 inch or even less. Shortening the gap increases the heat of the spark and nothing is gained by having it over 1/32 inch.

Almost all high tension magnetos have visible safety spark gaps that show instantly the presence of an open circuit in the secondary or high tension circuit. If an open circuit exists, a stream of sparks will flow across the safety spark gap at low speed.

To determine the cylinder that is misfiring in a four cylinder engine proceed as follows:

Remove cover on spark coil, and hold down one vibrator spring firmly against the core while the engine is running.

If the engine speed is not decreased by cutting this coil out of action, it is probable that this is the coil connected to the misfiring cylinder. Now release this vibrator and proceed to the next coil, and hold its vibrator down. If this decreases the speed of the engine you may be sure that the first coil is in the defective circuit. If the vibrator buzzes on the coil under inspection the trouble will be found in the plug.

Cutting out a coil connected to an active cylinder decreases the speed of the engine. Cutting out the coil connected with a dead cylinder makes no difference.

(97) Magnetos.

A magneto is a device that converts the mechanical energy received from the engine into electrical energy, the electricity thus produced being used to ignite the charge in the engine. This appliance does away with all of the troubles incident to a rapidly deteriorating chemical battery and produces a much hotter and uniform spark. A magneto is especially desirable with multiple cylinder engines where the demand for current is almost continuous, as the amount of current delivered by the magneto has no effect on its life or upon the quality of the spark.

The principal parts of the generating system of the magneto are the magnets, the armature, the armature winding, and the current collecting device, of which the armature and its windings are the rotating parts. The production of current in the magneto is the result of moving or rotating the armature coil in the magnetic field of force of the magnets. When any conductor is moved in a space that is under the influence of a magnet a current is generated in the conductor which flows in a direction perpendicular to the direction of motion. The value of the current thus generated depends on the strength of the magnetic field, the speed with which it is cut, and the number of conductors cutting it that are connected in series. Roughly, the voltage is doubled, with an increase of twice the former speed, and with all other things equal, the voltage is doubled by doubling the number of conductors connected in series.

By employing powerful magnets, and a large number of conductors (turns of wire) on the armature it is possible to obtain sufficient voltage for the ignition system at a comparatively low speed. The number of amperes delivered depends principally upon the internal resistance of the armature and the external circuit, and not on the number of conductors, nor directly upon the strength of the field. For this reason, low voltage machines that are intended to deliver a great amperage have only a few conductors of large cross section, while high tension machines have a great number of conductors of small size. In all cases the magneto, or ignition dynamo must be considered simply as a generator of current in the same way that a battery is a source of current since the current generated by them is utilized in precisely the same way.

The class of ignition system on which the magneto is used determines the class of the magneto. The low tension magneto is used principally for the make and break system, although it is sometimes used in connection with a high tension spark coil or transformed in the same way that a battery is used with a vibrator coil. The high tension magneto is used exclusively with the jump spark system and high tension spark plug.

These classes are again subdivided into the direct and alternating current divisions, depending on the character of the current furnished by the magneto. Briefly a continuous current is one that flows continually in one direction while an alternating current periodically reverses its direction of flow. As the alternating current magneto is the most commonly used type, we will confine our description to this class of magneto. The alternating current magneto is much the simplest form of machine as it has no commutator, complicated armature winding, nor field magnet coils, and in some types the brushes and revolving wire are eliminated.

As the magnetic flux of an alternating magneto is changed in value, that is increased and decreased, twice per revolution, it follows that the current changes its direction twice for every revolution of the armature. Each change in the direction of current flow is called an alternation.

The voltage developed in each alternation or period of flow is not uniform, the voltage being low at the start of the alternation, rapidly increasing in voltage until it is a maximum at the middle, and then rapidly decreasing to zero, from which point the current reverses in direction. As we have two such alternations, in a shuttle type magneto, per revolution we have two points at which the maximum voltage occurs; that is in the center of each alternation. These high voltage points are called the peak of the wave and consequently the sparking devices should operate at the peak of the wave or at the point of highest voltage. The spark therefore should occur when the shuttle or inductors are at a certain fixed point in the revolution at which point the peak of the wave occurs. The peak of the wave occurs when the shuttle is being pulled or turned away from the magnets.

In what is known as the “shuttle type” alternating current magneto, the generating coil is wound in the opening of an “H” type armature. This iron armature core is fastened rigidly to the driving shaft and revolves with it. As the armature revolves, it is necessary to collect the current that is generated by means of a brush that slides on a contact button B, the button being connected to one end of the winding.

(98) Low Tension Magneto.

The winding of the low tension magneto consists of a few turns of very heavy wire or copper strip, one end of which is grounded to the armature shaft and the other passing through the hollow shaft from which it is insulated. The end of the insulated wire is connected to the contact button (B) on which the current collecting brush presses. As one end of the winding is grounded, one brush, and one connecting wire is saved as the current returns to the magneto through the frame of the magneto. As the shuttle revolves between the magnet poles the magnetism is caused to alternate through the iron of the armature, thus causing the current to alternate in direction and fluctuate in value.

Since there are only two points at which the maximum current can be collected during a revolution with the alternating current magneto, it is necessary to drive it positively through gears, or a direct connection to the shaft so that this maximum point of voltage will always occur at the same point in regard to the piston position. If it is driven by belt without regard to the position of the piston, it is likely that there will be many times that the voltage is zero or too low in value when the spark is required in the cylinder. Alternating current magnetos must be positively driven, and the armature must be connected to the engine so that the peak of the wave occurs at, or a little before the end of the compression stroke.

With this type of magneto the only point that is likely to give trouble is the point at which the brush makes contact with the contact button. If the brush should stick or not make contact, or if the button is dirty or rusty, the current will not flow; this point should always be given attention. Outside of this the only attention necessary is to keep the bearings oiled.

Fig. 101 and Fig. 102 show the Sumter low tension magneto as arranged for make and break ignition. The armature and its connections are of exactly the same type as that shown in the previous diagram. The magnets and frame are arranged to tilt back and forth so that the peak of the wave will occur at the advanced and retarded positions of the igniter. This arrangement allows the full voltage of the magneto to be obtained at any point within the range of the ignitor, an important item when starting the engine or running at low speed. When mounted on the engine, as shown by Fig. 103, the magnets are provided with an operating rod that is marked “start” and “run.” When the pin on the engine bed is engaged under “start,” the magneto is retarded, when the pin is under “run” it is advanced. A number of intermediate points are provided at which the operating arm is held fast by tooth engagements as shown in the slotted handle. As shown in the illustration the magneto is fully advanced. The gears by which the magneto is driven are clearly shown in the cut, the ratio between the gear on the crank shaft and that on the magneto shaft being exactly 2 to 1. One lead is carried to the make and break igniter in the cylinder head, the current being returned through the bed of the engine. The same make of magneto is shown mounted on a vertical engine in Fig. 104. In this case the magneto is positively driven from the crank shaft of the engine by a chain. The single conductor running from the magneto to the cylinder heads is clearly shown. To start the engine, the igniter is set in the usual manner and the magneto tilted to starting position, as shown in the illustration. The engine is then started in the usual manner and, when running, the igniter is changed to running position, and the magneto is tilted outwardly. It is not important which is changed first, the magneto or the igniter. It is easy to remember the “starting” and running “position” of the magneto, the running position always being that in which the magnetos are tilted in the direction opposite to that in which the engine runs.

(99) Care of Low Tension Magnetos.

(1) Avoid setting a magneto on an iron or steel plate, unless stated otherwise in the manufacturer’s directions, as in some makes the magnetism will be short circuit by iron or steel and will reduce the output.

(2) Do not jar magnets or magneto unnecessarily, for this tends to weaken the magnets.

(3) Never remove the magnets if it can possibly be avoided. If this must be done, mark the magnets and gears so that they may be replaced in exactly the same position. If your magneto refuses to generate after reassembling it is probable that they are reversed in position or that the magnetism has been knocked out of them while off of the magneto.

(4) As soon as the magnets are removed, or better before, place a plate of iron or steel across both ends of the magnet. Don’t leave the magnets without this keeper for any length of time or they will lose their magnetism. The best plan is to leave the magnets alone.

(5) Remember that the running clearance between the magnets and armature is very small, only a few thousandths of an inch, and that any error in replacing the bearings in their proper position will cause the armature to bind in the tunnel. Handle armature carefully and do not lay it in a dirty place as a bent shaft or grit in the armature tunnel will fix it permanently.

(6) Most all magnetos are practically water proof, but don’t experiment with the hose.

(7) Make all connections firmly and have the wire clean under the binding posts.

(8) Only a few drops of oil are needed at long intervals, don’t neglect to oil them, but above all do not drown them with oil.

(9) Examine the brush occasionally and clean off all oil and dirt.

(10) When replacing the magneto on the engine after its removal see that the gears are meshed in the former position. Best to mark the teeth before removal.

(100) High Tension Magnetos.

The “true” high tension type magneto is complete in itself, requiring no jump spark coil nor timer, the high tension current being generated directly in the coils carried by the armature. This arrangement reduces the wiring problem to a minimum, as the only wires required are those leading directly to the spark plugs, and one low tension wire connecting the cutout switch used for stopping the engine.

The armature of this type of magneto carries two independent windings, one of a few turns of coarse wire called the primary coil, and the other consisting of thousands of turns of extremely fine wire called the secondary coil. It is in the latter coil that the high tension current is generated. The timer is connected directly to the armature shaft, and is an integral part of the magneto. All primary connections are therefore made within the magneto.

Belts or friction drives cannot be used with this type of magneto.

As there are no vibrators or independent coils used, the spark occurs exactly at the instant that the timer operates or breaks the primary circuit. It will be noted that the spark is produced with this magneto when the primary circuit is broken by the timer, instead of made as is the case with battery coils, or coils used with low tension magnetos. There is no lag and consequently the time of ignition is not affected by variations in the engine speed, which requires an advance and retard of the spark with batteries and vibrator coils.

When used with multiple cylinder engines the high tension magneto is provided with a distributor, which connects the high tension current with the different cylinders in their proper firing order. The timer determines the time at which the spark is to occur and the distributor determines the cylinder in which the spark is to take place.

The sparks delivered by the high tension magneto are true flames or arcs of intense heat, and exist in the spark gap for an appreciable length of time. It is evident that such flames possess a much greater igniting value than instantaneous static spark delivered by the high tension spark coil used with the battery or operated by the low tension magneto, and are capable of firing much weaker mixtures.

Like low tension magnetos, the true high tension type may be of either the inductor or shuttle wound class. All high tension magnetos are positively connected or geared to the engine in such a manner that there is a fixed relation between time of the current impulse produced by the magneto and the firing position of the engine piston.

The current is generated on the same principle as in the low tension shuttle type; that is, by a coil of wire revolving in the magnetic field established by permanent magnets.

During each revolution of the armature, two sparks are produced at an angle of 180° from each other.

The advance and retard of the spark is obtained by means of the timing lever which shifts the timer housing back and forth which results in the primary current being interrupted earlier or later in the revolution of the armature.

The timing lever can turn through an angle of 40° measured on the armature spindle, and the angle of advance for multiple engines is as follows:

Advance for 1 cylinder 40° Advance for 2 cylinders 40° Advance for 3 cylinders 50° Advance for 4 cylinders 40° Advance for 6 cylinders 27°

A timer is used with the magneto on a “jump spark” system in the same way as with a battery, providing a vibrating coil is used.

In one type of magneto the Connecticut, the coil is part of the magneto, and is fastened to the magneto frame. This type of magneto uses a non-vibrating coil, and produces but a single spark each time the primary circuit is broken by the magneto timer. As the timer on this type is driven by the magneto shaft, it is evident that the magneto must be “timed” with the engine, or must have its armature shaft connected to the shaft of the engine in such a manner that the timer contact is broken, and the single spark produced at the instant that ignition is required in the cylinder.

Unlike the dynamo, the alternating current magneto cannot be used with a storage battery, the alternating current producing no chemical change in the electrodes of the battery.

The Bosch high tension magneto is a typical high tension magneto having the primary and secondary windings wound directly on the armature shaft, there being no external secondary coil. The end of the primary winding is connected to the plate (1) Fig. 107, which conducts the current to the platinum screw of the circuit breaker (3). Parts (2) and (3) are insulated from the breaker disc (4), which is in electrical contact with the armature core and frame. When the circuit breaker contacts are together the primary winding is short circuited, and when they are separated the current is broken and the spark occurs. The breaker contacts are simply two platinum pointed levers that are separated and brought together by the action of a cam as they revolve. A condenser (8) is provided for the circuit breaker to suppress the spark and to increase the rapidity of the “break.”

The secondary winding of fine wire is a continuation of the primary winding, and the secondary is wound directly over the primary. The outer end of the secondary connects with the slip ring (9) on which slides the carbon brush (10), which conducts the high tension current from the armature. This brush is insulated from the frame by the insulation (11). From (10) the current is led through the bridge (12) through the carbon brush (13) to the distributor brush (15). Metal segments are imbedded in the distributor (16), the number of which corresponds to the number of cylinders. As the brush rotates, it makes consecutive contact with each of the segments in turn and therefore leads the current to the cylinders in their firing order. Wires from the cylinders are connected to sockets that in turn connect with the segments. The disc driving the distributor brush (15) is geared from the armature shaft in such a way that the armature turns twice for every revolution of the distributor, when four cylinders are fired, and three times for the distributors once when six cylinders are fired.

The voltage of the current generated in the secondary coil by the rotation of the armature is increased by the interruption of the primary circuit caused by the opening of the contact breaker.

At the instant of interruption of the primary circuit the high tension spark is produced at the spark plug.

As the spark must occur in the cylinder of the engine at a certain position of the piston, it is necessary that the interrupter act at a point corresponding to a definite position of the piston, consequently this type of magneto must be driven positively from the motor by means of gears, or directly from the shaft.

These magnetos run in only one direction. This running direction should be given when magneto is ordered, as being “clockwise” or “counter-clockwise” when looking at the driving end of the magneto.

The magneto for the single and double cylinder engines has no distributor, the high tension current being led directly from the armature.

The circuit diagram of the Bosch four cylinder magneto is shown by Fig. 108, the winding and plug connections being clearly shown. When connecting the magneto care should be taken to have the distributor and plug connections arranged so that the cylinders will fire in the proper order.

(101) Bosch Oscillating High Tension Magneto.

The oscillating type of magneto is used on slow speed heavy duty engines that move too slowly for the ordinary type of magneto. In the oscillating type the armature is given a short angular swing by the action of a tripping device operated by the engine which results in an intense spark at the lowest speeds.

Magneto type “29” is constructed with two powerful steel magnets, while magneto type “30” is provided with three; an armature of the shuttle type is arranged to oscillate between their pole-shoes.

The magneto is actuated by a rotating cam or other suitable device, which moves the armature 30° from its normal position whenever ignition is required. To permit this movement, a trip lever is mounted upon the tapered end of the armature shaft, this trip lever being held in a definite position by the tension of the spring or springs 1. The trip lever is only supplied when specially ordered, but each magneto is provided with the necessary springs and spring bolts.

When the trip lever is moved from its normal position by the operating mechanism, the springs are extended, and when the operating mechanism releases the trip lever, the later returns the trip lever and armature to their normal position, this movement resulting in the production of a sparking current in the armature winding.

The winding of the armature is composed of two parts, one being the primary winding, which consists of a few turns of heavy wire, and the other the secondary winding, which consists of many turns of fine wire.

The tension of the current produced by the oscillation of the armature is increased by closing the primary circuit at a certain position in its movement, and then interrupting it by means of the breaker. At the moment of the interruption, an arc-like spark is formed at the spark plug and ignition occurs.

On cam shaft (c) two cams are mounted side by side. One of these cams (a) is to be used for starting the motor, or for the retarded spark position, while the second (b) is to be used for operation, or for the full advance position. These cams are mounted on a sleeve, which may be moved longitudinally on the shaft, so that the trip lever may be operated by cam (a) or cam (b) as desired. The sleeve is caused to rotate with the shaft by a key. Between the cam (b) and a fixed collar (f) a spiral spring is arranged, which tends to maintain the sleeves in the position when the cam (b) is in operation. A stop collar is also provided to limit the movement of the sleeve beyond this full advance position. Over this collar is fitted a hand wheel, which, in the position illustrated in the diagram, acts together with the collar as a stop. Around the collar is a circular key-way, and a brass bolt is located in the hand wheel to lock into this key-way when the hand wheel is pushed into the position indicated by the dotted lines. This movement of the wheel forces the cam sleeve forward, and brings the retarded cam (a) into the operating position to permit the engine to be started.

(102) The Mea High Tension Magneto.

The low tension winding of the ordinary type of magneto is short-circuited by a breaker which opens at certain points of each revolution with the result that a high voltage is generated across the high tension winding at the moment of the break, and a spark produced across the spark gap in the cylinder to which it is connected. The quality of this spark, or in other words the heat value, depends among other factors upon the particular position of the armature in relation to the magnetic field at the moment the spark is produced. As the armature in this type of magneto is in a favorable position for obtaining a spark twice every revolution, two sparks can be obtained per revolution. The timing of the spark is accomplished by opening the breaker earlier or later, by shifting the breaker housing naturally with the unavoidable result that if the position of the magnetic field remains stationary, the relative position between armature and field at the moment of the break must vary. Since, however, as explained above, the quality of the spark depends upon this relative position, it is apparent that a good spark, can, with a stationary magnetic field, be produced only at one particular timing.

The result of these conditions are known to everybody familiar with automobiles. They are the difficulty of cranking a motor on one of the average high tension magnetos, if the spark is fully retarded, and of operating the motor on the magneto at very low speed, particularly when it is overloaded, as for example, in hill climbing. Attempts have therefore been made to obtain the spark, independent of the timing, always at the same favorable position of the armature.

The distinct innovation and improvement incorporated in the Mea magneto consists in bell shaped magnets (Fig. 111) placed horizontally and in the same axis with the armature, instead of the customary horse-shoe magnets placed at right angle to the armature.

This at once makes possible and practicable the simultaneous advance and retard of magnets and breaker instead of the advance and retard of the breaker alone as the magnets may be moved to and fro with the breaker housing. It will be seen that as a result of this new departure the relative position of armature and field at the moment of sparking is absolutely maintained, and the same quality of spark is therefore produced, no matter what the timing may be. Furthermore, the range of timing, which with the horse-shoe type of magneto is limited to 10° or 15° at low speeds (i. e. at speeds at which a retarded spark is of value) becomes limited only by the necessity of supplying a suitable support for the magnets. With the standard types of Mea magnetos described in the following, this range varies from about 45° to 70°, but if necessary this range can be increased to any amount desired.

The bell-shaped magnets are fixed to the casing which is mounted on a base supplied with the magneto. The timing is altered by turning the casing and magnets together on the base.

Fig. 112 shows a longitudinal section of a four cylinder Mea magneto. The armature F with the ball bearings 17–18 rotates in the bell-shaped magnets 100, the poles of the magnets being on a horizontal line opposite the armature 1. The armature is of the ordinary H type iron core wound with a double winding of heavy primary and fine secondary wire. On the armature are mounted the condenser 12, the high tension collector ring 4, and the low tension circuit breaker 26–39.

The circuit breaker consists of a disc 27 on which are mounted the short platinum 33, the other contact point 34 is movable and is supported by a spring 30 which is fastened to the insulated plate 28 mounted on disc 27. Fiber roller 31 in connection with cam disc 40 which is provided with two cams is located inside the breaker. Revolving with the armature the roller presses against the spring supported part of the breaker whenever it rolls over the two cams which of course is twice per revolution.

Inspection of the breaker points is made easy by an opening in the side of the breaker box. The box is closed by a cover 74 supporting at its centre the carbon holder 47 by means of which the carbon 46 is pressed against screw 24. This latter screw connects with one end of the low tension winding while the other end is connected to the core of the armature. It will, therefore, be seen that the breaker ordinarily short-circuits the low tension winding and that this short-circuit is broken only when the breaker opens; it will also be apparent that when the screw 24 is grounded through terminal 50 and the low-tension switch to which it is connected, the low-tension winding remains permanently short-circuited, so that the magneto will not spark. The entire breaker can be removed by loosening screw 24.

The high tension current is collected from collector ring 4 by means of brush 77 and brush holder 76, which are supported by a removable cover 91 which also supports the low tension grounding brush 78 provided to relieve the ball bearings of all current which might be injurious. Cover 91 also carries the safety gap 89 which protects the armature from excessive voltages in case the magneto becomes disconnected from the spark plugs.

The distributor consists of the stationary part 70 and the rotating part 60 which is driven from the armature shaft through steel and bronze gears 7 and 72. The current reaches this distributor from carbon 77 through bridge 84 and carbon 69. It is conducted to brushes 68 placed at right angles to each other and making contact alternately with four contact plates embedded in part 70. These plates are connected to contact holes in the top of the distributor, into which the terminals of cables leading to the different cylinders are placed.

In the front plate of the magneto is provided a small window, behind which appear numbers engraved on the distributor gear which correspond to the number of the cylinder the magneto is firing. This indicator is of great value as it allows a setting or resetting after taking out, without the necessity of opening up the magneto to find out where the distributor makes contact.

The magneto proper is mounted in the base 53 which is bolted to the motor frame and the arrangement is such that the magneto can be removed from its base by removing the top parts 60a and 60b of the two bearings. The variation in timing is affected by turning the magneto proper in the stationary base which is accomplished by the spark lever connections attached to one of the side lugs 88. The spark is advanced by turning the magneto opposite to rotation and is retarded by turning it with rotation. One cylinder magnetos are similar to the four cylinder except that the distributor and gears are omitted.

(103) The Wico High Tension Igniter.

The Wico igniter produces a spark similar to that of the conventional high tension magneto except that the heat of the spark is independent of the engine speed. In other respects it is very different from the types described in the preceding pages for its motion is reciprocating instead of being rotary, and because all of the wire is stationary, the only movement being that of the iron core that passes through the center of the fields. The fact that the spark is of the same intensity at all speeds makes this device particularly desirable in starting the engine at which time the mixture is always of the poorest quality.

It is very simple, and is without condensers, contact points or primary windings, and has no parts that require adjustment.

The current is generated by the reciprocating movement of two soft iron armatures shown as a bar across the bottom of the two coils, which move alternately into and out of contact with the ends of the soft iron cores. The movement of these armatures in the upward direction is produced by the motion of the engine and the speed of this movement is, of course, proportional to the speed of the engine. The downward movement, which produces the spark, is caused by the action of a spring, is much more rapid than the upward movement and entirely independent of the speed of the engine.

The magnets are made of tungsten steel, shown as two bars across the top of the coils, hardened and magnetized and are fastened by machine screws to the cast iron pole pieces, which serve to carry the magnetic lines of force from the poles of the magnets to the soft iron cores. The cores, which fit into slots milled in the pole pieces, are laminated or built up of thin sheets of soft iron, each sheet being a continuous piece, the full length of the core. Each core, extends from just below the top armature, down through the pole piece, and coil to just above the bottom armature.

Each armature consists of a number of laminations or sheets of soft iron mounted on a spool shaped bushing, which, in turn, is loosely fitted onto the squared end of the armature bar. The armature bar is supported with a sliding fit in a box shaped guide which is fastened in the case.

On the outer ends of the armature bar are spiral springs held in place by cup shaped washers and retaining pins, the combination making a self-locking fastening similar to the familiar valve spring fastening used almost universally on gas engines. These springs bear against the armatures and tend to force them against the shoulders of the armature bar.

The coils each have a simple high tension winding of many turns, thoroughly insulated and protected against mechanical injury. They are connected together in series by means of a metal strip, thus making one continuous winding. In the single cylinder igniter, one end of the winding is grounded to the case of the igniter, while the other end is connected to the heavily insulated lead wire. This lead wire passes out through a stuffing box, packed with wicking and thoroughly water tight, direct to the spark plug in the cylinder.

In the two cylinder machine no ground connection is used, but both ends of the winding are connected to lead wires passing out of the case to the spark plugs.

The action of the igniter is as follows:—As the driving bar, through its connection with the engine, is moved downward to its limit of travel, carrying the latch with it, the shoulder on the side of the latch snaps under the head of the latch block. As the motion reverses the latch carries the latch block and armature bar upward. The lower armature, being in contact with the stationary cores, cannot rise with the armature bar, but the lower armature spring is compressed between its retaining washer and the armature, while the bar rises and carries with it the upper armature, which bears against the upper shoulders on the bar.

As the driving bar continues its upward motion the upper end of the latch meets the lower end of the timing wedge and, as the wedge is held stationary by the timing quadrant, a further movement of the latch causes it to be pushed aside until the shoulder on the latch clears the latch block and releases it.

As the lower armature spring is at this time exerting a pressure between the armature bar and cores through the medium of the lower armature, the instant the latch block is released, the armature bar is quickly pulled downward, carrying the upper armature with it. Just before the motion of the upper armature is stopped by its coming in contact with the cores, the lower shoulders on the armature bar come in contact with the lower armature, and, as the bar has acquired considerable velocity, its momentum carries the lower armature away from the cores against the pressure of the upper armature spring, which thus acts as a buffer to gradually stop the movement of the armature bar. The armature bar finally settles in a central position.

The timing of the spark is accomplished by releasing the armature bar earlier or later in the stroke. This is done by shifting the position of the eccentric timing quadrant, which in turn varies the position of the wedge so that the latch strikes it earlier or later in the stroke. The timing quadrant is furnished with several notches into one of which the top of the wedge rests, thus holding the quadrant in the desired position.

The motion should preferably be taken from an eccentric on the cam shaft of a single cylinder four cycle engine, or the crank shaft of a single cylinder two cycle or a two cylinder four cycle engine. On a two cylinder four cycle engine, it is sometimes more convenient to drive the igniter from the cam shaft, using a two throw cam to produce the required number of sparks. In this case the shape of the cam should be such as to duplicate the motion of the eccentric. That is, it should start the driving bar slowly from its lower position, move it most rapidly at mid stroke and bring it to rest gradually at the upper end of the stroke, exactly as is done by the eccentric motion.

When an eccentric is already on the engine the motion may be taken from it to an igniter with a driving bar through a properly proportioned lever that will give the required length of stroke. Where a plunger pump is used on the engine the motion can usually be taken from the pump rod. Where an eccentric has to be provided especially for the igniter, the driving bar is generally used with its roller running on the eccentric.

(104) Starting On Magneto Spark.

A four-cylinder engine in good condition will come to rest with the pistons approximately midway on the stroke and balanced between the compression of the compressing cylinder and of the power cylinder. When the cylinders of such an engine are charged with a proper mixture, the engine will start by the ignition of the mixture contained in the compressing cylinder, for the pressure produced by the ignited gas will be sufficient to rotate the crankshaft.

It is essential, for the ignition system to be so arranged that a spark can be produced at any point in the piston travel, and in this the Bosch dual, duplex and two independent systems are successful.

The Bosch dual system, Fig. 114, is part of the equipment of many of the cars and engines marketed, and is composed of two separate and distinct ignition systems, one supplying ignition by direct high-tension magneto, and the other by a battery and high-tension coil. These two systems consist in reality of but two main parts; the dual magneto, incorporating a separate battery timer, and the single unit dual coil with its battery. The sparking current from either battery or magneto is brought to the magneto distributor, so that the only parts used in common are the distributor and the spark plugs; the common use of the latter for both magneto and battery systems is cause for the popularity of the dual system for motors having provision for only one set of plugs.

In both the magneto and the battery sides the spark is produced on the breaking of the circuit, and the coil is so arranged that by pressing a button when the switch is in the battery position, an intense vibrator spark is produced in the cylinder during that period when the circuit breaker is open, which will be the case during the first three-fourths of the power stroke. The current is transmitted to the distributor and passes through the spark plug of the cylinder that is on the power stroke.

Should the engine come to a stop in such a position that the battery timer is closed, it will not be possible to produce a vibrator spark by the pressing of the button, but the releasing of the button will produce a single contact spark that will ignite the mixture and thus start the engine.

Thus if the engine should stop in some odd position, and the spark is produced when the piston is slightly before top center, for instance, there will be a slight reverse impulse which will bring another cylinder on the power stroke and into the ignition circuit. The engine will thereupon take up its cycle in the proper direction.

In the Bosch duplex system the coil is in series with the magneto armature, but the spark is produced under the same condition, that is, on the breaking of the circuit. In consequence the Bosch duplex system will permit the production of a spark during the first three-quarters of the power stroke by the pressing of the push button set on the switch plate.

The Bosch two independent system is composed of a separate Bosch battery system and a separate Bosch magneto. Although the operation of the coil is somewhat similar to that of the dual system, the nature of the battery system is such as to require arrangements for two separate sets of spark plugs. The coil is not unlike that supplied with the dual system in that by pressing a button located on the switch plate a series of intense sparks may be produced in the cylinder at all advantageous points of the power stroke.