CHAPTER V

TYPICAL FOUR STROKE CYCLE ENGINES

(41) Essential Parts of the Gas Engine.

On all gas engines of accepted type are found certain devices necessary for the performance of the events or cycles outlined in the preceding section.

For the sake of simplicity these devices are treated as a part complete in itself. The details of construction, and the refinements found necessary in the actual construction will be described in the succeeding chapters.

The names and purpose of these essential components, and their relation to the operation of the engine as a whole, will be found in the following outline:

1. The =CARBURETOR= is a device whose purpose is to vaporize the liquid fuel, and mix the vapor thoroughly and in correct proportions with the air required for the combustion, in the engine cylinder.

The combustible mixture thus formed is drawn into the cylinder of the four stroke cycle engine or into the crank chamber of the two stroke cycle engine.

=GENERATOR VALVES= or =MIXING VALVES= are similar to the carburetor in principle but are slightly different in detail.

2. The =CYLINDER= is the containing vessel in which the combustion and expansion of the gas takes place.

The cylinder as its name would suggest has a circular opening or bore extending from end to end, the bore being smoothly finished to receive the reciprocating piston.

3. The =PISTON= is a plunger or movable plug fitting the bore closely enough to prevent the escape of gas, but at the same time is capable of sliding freely to and fro.

When pressure is established in the cylinder from the combustion, pressure is also exerted on the end of the piston tending to force it out of the cylinder. The extent of this force is governed by the area of the end of the piston and also by the pressure of the gas.

Thus the purpose of the piston is to convert the pressure of the expanding gas into direct mechanical force, and also to transform the increasing volume of gas into motion. Another, and no less important function of the piston is to compress the combustible gas in the upper end of the cylinder for ignition.

4. The =CONNECTING ROD= (Sometimes called the Pitman) transmits the pressure on the piston to the crank, the connecting rod being the means through which the to and fro motion of the piston is transmitted into the rotary motion of the crank; its action being similar to that of the human arm turning the crank of a pump or windlass.

5. The =CRANK= receives the pressure and motion of the piston from the connecting rod, changing the reciprocating motion of the piston into the rotary motion required by the machinery which the engine drives.

In the majority of cases the crank revolves, while the cylinder stands still, but in some of the recently developed aeronautic motors this is reversed, the cylinders revolving with the crank stationary. The relative motion, however, is the same in both cases.

(6.) The =CRANK SHAFT=, of which the crank is an integral part, transmits the rotary motion of the crank to the driving pulley.

(7.) The admission and release of the gases to and from the cylinder are controlled by the =INLET VALVE= and =EXHAUST VALVE=, respectively, in a four stroke cycle engine.

The valves are merely gates, allowing the gas to flow, or stopping it, at the proper intervals, depending on the event taking place at that time in the cylinder.

In the two stroke cycle engine there are no valves, the admission and release of the gas being controlled by the position of the piston, and the openings cut in the cylinder walls.

6. =IGNITION= or the firing of the combustible charge is accomplished by the =IGNITION SYSTEM=. In most modern engines the mixture is ignited when it is under the greatest pressure or at the end of the stroke.

For maximum efficiency the mixture should be ignited when it is under the greatest pressure or compression. The time at which ignition occurs is also controlled by the ignition system.

7. The =GOVERNOR= regulates the speed of the engine; either by changing the richness of the mixture, by changing the number of working strokes in a given time or by altering the quantity of gas admitted to the cylinder, or sometimes by a combination of these methods.

8. The =BELT WHEELS= or =PULLEYS= are the means of transmitting the power of the engine to the work to be performed. The engine is generally connected to the driven machinery by a belt connecting the engine pulley with the pulley of the driven machine.

9. The =FLY WHEELS= by reason of their mass and their momentum, store up a portion of the energy expended during the working stroke, and return it to the engine in order to carry it through the idle strokes of compression, admission and expulsion. In some engines the fly wheels serve in double the capacity as pulleys.

10. The =BASE= or =FRAME= of the engine acts as a foundation for the various working parts, holding them in their proper positions.

(42) Application of the Four Stroke Principle.

While the five events of every commercial four stroke cycle engine are accomplished in exactly the same order, or routine as explained in paragraph (8), Chapter 3, the actual design and method of applying the cycle varies greatly in different makes of engines. This great difference in the details of construction often makes it difficult for the novice to identify the cycle of operations in that particular engine. The different forms of valve gears that are used to perform the same functions in the cycle are good examples of the variation in design, some makers using the poppet or disc type, some the sliding sleeve, and others the rotary type.

Multiple cylinder engines vary in the cylinder grouping or arrangement, the arrangement and number of cylinders depending on the service for which the engine is intended, the amount of vibration permissible, or the weight. The question of speed also introduces modifications in the design, but no matter what valve arrangement is adopted or what grouping of cylinders is used, a four stroke cycle engine performs the five events of suction, compression, ignition, expansion and exhaust in four strokes, in each and every cylinder. With the exception of fuel injection (which in reality corresponds to the ignition event) in the four stroke Diesel engine, the indicator cards of all four stroke cycle engines passes the same characteristics as the diagram shown in Fig. 10.

In this chapter, the engine will be described without regard to the fuel used, or to the means adopted in vaporizing it, for the vaporizing appliances are considered as being external to the engine proper, except in some of the heavy oil engines, and as the fuel is gasified before entering the cylinder the question of fuel does not affect the general construction of the engine. The majority of engines are readily converted from gasoline to gars, or in some cases kerosene, by changes in the vaporizing device, and with the exception of changing the compression pressure, little further alteration is needed. Since the vaporization and admission of the heavier oils, such as crude oil and kerosene has a more intimate relation to the engine than the use of gasoline or gas, the heavy oil engines will be described in a separate chapter in order that the process of oil burning may be more fully explained. It should not be understood that the cycle, or principle of the oil engine differs from that of any other engine, but that the vaporizer forms such a close connection with the engine proper that they must be described as one unit.

(43) Horizontal Single Cylinder Engine.

An example of a modern single cylinder engine operating on the four stroke cycle principle is the “Muenzel” engine shown in Section by Fig. 17. It is of the single acting type, that is, the pressure of the gases acts only on the left end of the piston which reciprocates in a horizontal direction. Surrounding the cylinder in which the piston slides, is the water jacket (shown by the short horizontal dashes) which keeps the cylinder walls from becoming overheated by the successive explosions of the mixture. The cooling water is pumped into the jacket through the pipe shown over the cylinder, and flows out of the jacket through an outlet near the bottom of the cylinder.

Both the inlet and exhaust valves are situated in an extended portion of the combustion chamber to the left of the piston, the upper valve being the inlet and the lower valve, the exhaust. The valves are held on their seats by means of coil springs that act on the upper ends of the valve springs. Admission of the explosive mixture is controlled by the upper valve, and the release of the burnt gases by the lower. Pipes at the bottom of the cylinder marked “Gas Supply” and “Exhaust” convey the gases to and from the inlet and exhaust valves respectively.

The inlet valve, and the inlet valve spring are held in one unit by a removable metal housing known as a “Valve Cage”, which is arranged so that the cage, valve, and spring may be removed as one piece from the cylinder casting when the valves need attention by removing a few bolts. As the cage is directly over the exhaust valve, and is considerably larger in diameter, it is possible to remove the exhaust valve through the opening left by the removal of the inlet valve cage. Both valves are surrounded by a water jacket, as are the passages that lead to them.

Both the inlet and exhaust valves are opened and closed at the proper moments in the stroke by means of cams mounted on the horizontal cam shaft shown by Fig. 18 through a system of levers. The cam shaft is the shaft running parallel to the engine bed from the crank-shaft to the end of the cylinder and turns at one-half the speed of the crank-shaft. At a point directly below the inlet valve in Fig. 18, will be seen an enlargement on the shaft on which rests the rod running from the inlet valve to the cam shaft. This is the cam.

A cylindrical casing shown above the cylinder contains the governor which maintains a constant speed at all loads by operating a valve in the intake pipe which varies the quantity of mixture entering the cylinder in proportion to the load. The governor is driven from the cam-shaft by spiral gears. The igniter which furnishes the spark for igniting the gas is located between the two valves at the extreme left of the combustion chamber (Fig. 17).

It should be noted that the cylinder head which closes the left end of the cylinder, and which carries the valves is separate from the main body of the Cylinder. By unscrewing the bolts that hold it to the cylinder, the head may be removed when it becomes necessary to remove dirt and carbonized oil from the combustion chamber, or when it becomes necessary to remove the piston. The cylinder barrel in which the piston works may also be removed through the opening left by the piston head when it becomes worn, and another barrel or liner may be substituted, thus practically renewing the engine at a small fraction of the cost of a new cylinder. The liner is fastened firmly to the outer cylinder casting at the left but is free to slide back and forth in the casting at the right hand end, this end being provided with a packed joint. This play given to the liner allows it to expand and contract freely with the different changes of temperature without causing strains either in the cylinder or in the liner.

(44) Multiple Cylinder Engines.

Since the power exerted by a single cylinder four stroke cycle engine is intermittent, the explosive force exerted on each power stroke is much heavier than would be the case if the power application were continuous, as the explosions must be heavier to compensate for the idle periods. To reduce the strain on the engine and the vibration as well and to obtain an even turning moment it has been customary to provide more than one cylinder on engine of over 10 horse-power capacity. In this way the total power is divided among a number of cylinders, and as no two cylinders are under ignition at any one time the turning moment is more even, the vibration is less, and the strain on the engine is considerably reduced.

Dividing the power in this way makes it possible to reduce the weight of the engine as less material is required to resist the strains and a small fly-wheel may be used because of the even engine torque. In order to gain the full benefit of this reduction in weight, the builders of aeronautic motors have carried the multiplication of cylinders to an extreme, the Antoinette for example having sixteen cylinders. Engines having more than six cylinders exert a continuous pull as the impulses “overlap,” that is, ignition occurs in one cylinder before another cylinder in the series ends its working stroke. The greater the number of cylinders, the more continuous will be the torque or turning moment. The multiple cylinder engine may be considered as a group of single cylinder engines connected together, and receiving their fuel from a common source, the only difference between the single and multiple being in the inlet and exhaust piping and the ignition system.

As a single cylinder four stroke cycle engine has one working impulse in every two revolutions, a two cylinder engine will have an impulse for every revolution as there are twice as many impulses in the same time. It should be remembered that the number of impulses given per revolution by a four stroke cycle engine is equal to the number of cylinders divided by two. Thus, a six cylinder engine has 6 ÷ 2 = 3 impulses per revolution, and an eight cylinder, 8 ÷ 2 = 4 impulses, providing of course, that the engine is single acting.

Arrangement of the cylinders varies with the service for which the engine is intended and the perfection of balance that is required, the principal arrangements being the “V,” the “upright,” the opposed, the “radial,” “tandem,” and “twin.” The upright engine has the cylinders all on one side of the crank-shaft in a straight line, as in the four cylinder automobile engine. In this form, each cylinder has an individual crank throw the number of throws being equal to the number of cylinders. This engine is fairly well balanced in the four, six and eight cylinder types, as one-half of the connecting rods and throws are up, while the other half are down, but as the connecting rods do not all make equal angles with the center line of the cylinder at the same time there is a slight unbalance in the four and six cylinder types. Because of the ignition sequence, two cylinder vertical motors are in no better balance than the single cylinder type since both crank throws and connecting rods are on the same side of the shaft at the same time. For this reason the two cylinder engine is most commonly built in the opposed type which gives perfect balance.

In “V” type arrangement, one-half of the cylinders are set at an angle of about 90° with the rest of the cylinders, or in the two cylinder “V” the cylinders are set in the same plane, perpendicular to the shaft, at angle varying from 57½° to 90°. The “V” type arrangement is adopted where light weight and compactness are the principal requirements, as the weight and length are both reduced by putting the cylinders opposite to one another by pairs, the “V” being practically one-half the length of an upright having the same number of cylinders. This arrangement permits the use of one-half the number of crank throws used in the vertical type as each crank throw acts for two cylinders. For the reason that both the cylinders of a two cylinder “V” act on a common crank throw, the two cylinder “V” is in no better balance than a single cylinder engine.

An “opposed” type engine is in the most perfect mechanical balance of any engine as the crank shafts and connecting rods are not only on opposite sides of the crank-shaft, but make equal angles with the center line of the cylinders as well, at all points in the revolution. The explosive impulses occur at equal angles in the revolution as in the four and six cylinder vertical type. An opposed engine may be considered as a “V” having a cylinder angle of 180°. In the opposed type, one crank throw is provided for each cylinder, the pistons of the opposite cylinders traveling in opposite directions at the same time.

A “radial” or “Fan” type motor, as the name would suggest has the cylinders arranged in one or two rows around the crank case, each cylinder being on a radial line passing through the center of the cylinder with one crank throw for each row. The Gnome engine illustrated elsewhere in the book is an example of this type, the seven equally spaced cylinders acting on a common crank throw. When more than seven cylinders are used on this engine, as in the fourteen cylinder engine, two cranks are provided, each crank serving seven cylinders. This arrangement cuts down the weight of a motor enormously because of the short crank shaft and case. With the ignition properly timed and the cylinders correctly spaced the firing impulses occur at equal angles.

“Tandem” cylinders are employed only on stationary engines, the cylinders being placed on the same center line, one in front of the other, and when this arrangement is adopted it is the usual practice to make the cylinders double acting. The two pistons are connected by a rod known as the “piston rod” which extends from the rear end of one cylinder into the front of the following cylinder. Tandem cylinders require too much room for use on automobiles or motor boats, and for this reason are seldom seen in this service.

The “twin” engine is a modification of the vertical cylinder arrangement, both cylinders being on the same side of the shaft and in line with one another. It is the type most generally used on very large stationary engines that have more than one cylinder, and instead of being vertical as in their prototype are generally laid horizontally. Since the twin engine is generally double acting, the crank throws are placed on opposite sides of the shaft.

(45) Four Cylinder Vertical Auto Motor.

A common type of four cylinder vertical motor is shown by Fig. 19, which is of the type commonly used on automobiles. In order to show the general construction of the cylinder, each cylinder is cut through at a different point. The cylinder at the extreme left is shown in elevation, or as we would see it from the outside. In the second cylinder from the left, the section is taken through the valve chamber, which projects from the side of the cylinder. A section through the center of the cylinder is shown on the third cylinder, and the fourth cylinder is in elevation.

On cylinder No. 1, (left) is seen the exhaust pipe (32) and the inlet pipe (31) entering to valve chamber and connected to the exhaust valve and inlet valve respectively. The pipes are held in place by the clamp or “crab” (33). The exhaust pipe connects with the exhaust valve of each cylinder, and terminates at the fourth cylinder as shown by (32). Screwed into the top of the valve chamber on cylinder No. 1 are the two spark plugs (34) and the relief cock (35).

Referring to cylinder No. 2, the inlet valve (42) is shown at the left of the chamber and the exhaust valve also shown by (42) is shown at the right. Above the valves are the spark plugs (34) which project into the space above the valves. Pressing against the lower ends of the valve stems and holding the valves tight on their seats are the springs (44) which fit into the washers (45) fastened to the stems. The valve stems terminate in a nut at (48). The valve stem guides (43) form a support for the valves and at the same time form an air tight connection for the stems to slide in.

Immediately beneath the stems are the push rods (46) which are provided with an adjustment (48) at the upper end, and a roller (49) at the lower end. The rollers (49) rest directly on the cams mounted on the cam shaft (27), and as the irregular cams revolve, the push rods are moved up and down which in turn act on the valve stems and raise the valves at the proper moment. The cams raise the valves and the springs close them. The two cams (exhaust and inlet) appear as two rectangular enlargements on the shaft (27). The bearings (53), support the cam shaft, one being supplied for each cylinder.

At the extreme left of the crank shaft is shown the half time gear (20) which meshes with the gear on the crank-shaft and drives the cams. Next to this gear is the large cam shaft bearing 26. It should be noted that the section through the valve chamber taken on cylinder No. 2 is at a point considerably back from the center line of the cylinders and not in the same plane as the section shown on cylinder No. 3, which is taken through the center line of the cylinders.

In the section of cylinder No. 3, we see the water space surrounding the upper portion of the cylinder with the opening (37) connected to the water manifold (36), through which the water leaves the cylinder and passes to the radiator. At the lower end of the stroke is the piston, one-half of which is shown in section and one-half in elevation so that internal and external appearance may be readily seen. The piston pin (60) is located approximately in the center of the piston to which it is secured by means of the set-screw (61).

By means of the connecting rod (56), the motion of the piston is transmitted to the crank-shaft throw (54), both ends of which are provided with bronze bushings (59) and (58), fitting on the piston pin and crank-pin respectively. Between each crank throw are the main crank shaft bearings (55) which are provided with the bronze bushings (54). Below the connecting rod ends is the small drip trough containing oil into which the pipes on the rod ends dip when passing around the lower end of the stroke. When the pipes enter the oil puddle a small amount of lubricating oil is driven into the crank-pin bearing because of the force of impact, this force also causing oil to splash about in the crank case for the lubrication of the main crank shaft bearings and cam shaft. In order to maintain a constant level of oil in the puddle so that the bearings shall receive a constant supply of oil, a small overflow opening is placed in the center of the puddle which allows an excess of oil to overflow into the return oil sump below.

This excess of oil drains by gravity back to the oil circulating pump (73), at the right which again forces the oil to the various bearings. In this way, the same oil is used over and over again until it becomes unfit for lubricating purposes because of dirt or decomposition. The oil pump is driven from the cam-shaft through the level gears (66) and the vertical shaft (72). To the right of the oil pump is the fly-wheel (75) which furnishes the power for the idle strokes of the engine.

At the upper end of the vertical shaft that drives the oil pump is an extension (68) which passes through the bearing (70) and drives the ignition timer shown at the top of the housing (69). The timer controls the period of ignition in the cylinders in regard to the piston position so that the spark occurs at the end of the compression stroke. At the extreme left of the engine is the radiator fan (1) which is driven from the crank-shaft pulley (16), the belt (10), and the fan pulley (1122). This fan increases the amount of cold air that is drawn through the radiator, (mounted to the left of the engine) and increases its capacity for cooling the jacket water of the engine. The water circulating pump is located on the opposite side of the motor.

In this motor both the inlet and exhaust valves are located on the same side of the cylinder which arrangement classifies the engine as an “L” type, the extended valve pockets forming an “L” with the center line of the cylinder. In the motor shown by Figs. F-14-F-15, the inlet and exhaust valves are on opposite sides of the cylinder as shown in the cross-section, which classifies the motor as a “T” type, as the valve chambers together with the cylinder forms a “T.” The latter type of motor has several advantages over the “L” type, but as it requires two cam shafts, one for the inlet and one for the exhaust valves, it is not adopted by the builders of the cheaper grades of automobiles. Since the exhaust valves are on the opposite side of the cylinder, in the “T” type, the inlet air is not expanded nor the output diminished by the heat of the exhaust passages. The piping is less complicated which permits of a more effective arrangement of the carburetor and magneto. Since the piping in the latter type can be arranged to better advantage, less back pressure is the result.

As in the previous case, the valves are acted on directly by the cams and push rods, one cam shaft being provided on each side of the cylinders. In order to reduce the noise made by the push rods and springs, all of the springs are enclosed by sheet metal housings or tubes. The circulating pump is shown at the left nearly on a line with the left hand cam shaft, the pump outlet being inclined toward the cylinder so that it enters the water jacket under the exhaust valves. Water leaves the jacket by the pipe shown on the cylinder tops.

From the longitudinal section it will be seen that the cylinders are cast in pairs, two cylinders to the pair, instead of singly as in the previous case. The large pipe crossing at about the center of the cylinders is the exhaust pipe (shown in front of the left pair), and the pipe shown under the exhaust is the water inlet pipe from the circulating pump. It will be seen from the longitudinal section that the main crank-shaft bearings are fastened to the upper half of the crank case, and are entirely independent of the lower half which acts simply as an oil shield. This construction allows the oil shield (lower half) to be removed without disturbing the adjustment of the bearings, when it becomes necessary to inspect the internal mechanism.

Large removable plates cover the top of the water jackets so that it is a simple matter to clean out the water space in case that it becomes coated with deposits from the water. This is an important feature as a great many of the heating troubles may be overcome by having access to the interior of the water jacket. The water outlet pipes connect with the jacket covers. Both cam shafts are driven by the gears at the right which connect with the crank shaft pinion. Fan is belt driven from an extension to the cam shaft.

All bearings are supplied with oil by a high pressure force feed pump, the crank pins receiving their supply through channels drilled in the crank shaft and pin, which in turn are connected to the oil supply of the main bearings, no dependence being placed on a splash system. After leaving the bearings, the oil drops into the crank case and drains into the sump shown at the left of the longitudinal section. From the sump, the oil returns to the oil pump from which point it is returned to the circulating system under high pressure.

(46) Stationary Four Cylinder Engine.

An English stationary engine, the Browett-Lindly, similar in many respects to the automobile engines just described, is shown in longitudinal and cross-section by Figs. 20 and 21. This is of the “L” type of valve arrangement, but instead of having the valves side by side as in the preceding case, the inlet valve is placed over the exhaust as will be seen from the cross-section view.

The exhaust valve is operated directly from the cam shaft by the push rod as in the auto engines, but the inlet valve receives its motion through a long vertical rod and horizontal lever, the latter being located on the cylinder head as shown by the longitudinal section. A supplementary valve is mounted loosely on the stem of the inlet valve, and this valve is held against the seat of the gas inlet port by a short spring.

A collar on the main valve spindle opens this gas valve, and, by adjusting the position, a certain amount of lag can be given, so that air first enters the cylinder and then, by further travel of the main valve, the gas valve opens and the combined charge is taken in. This prevents any “back fires” as the gas and air are entirely separated until they enter the cylinder.

Starting is effected by means of compressed air, and is entirely automatic. No compression release is provided, as this is unnecessary under the system adopted. By opening the main compressed air valve compressed air is admitted to two valve boxes placed underneath the cam shaft, and the pressure of air raises the valves against their levers and cams. Should the swell on the cam be opposite a lever as it will be in the correct starting position, the valve cannot close, and the compressed air then passes to the cylinder through a check valve on the face of the cylinder, and the engine starts. The automatic check allows the cylinders to take in a charge of mixture on the second stroke and firing takes place immediately. When the explosion pressure is greater than the air pressure the check remains closed and no more starting air enters the cylinder.

Governing is effected by varying both the quantity and quality of the mixture.

The main valve, plunger, and rod springs, and all springs on the valves and valve motion, are arranged to be in compression. The exhaust valves are of cast-iron, and are fitted with renewable seats in the cylinders. The admission valves are of nickel steel, and are arranged in boxes, which, when removed from the cylinders, provide the ports which give access to and space for the removal of the exhaust valves which are withdrawn vertically.

Forced lubrication is fitted throughout all bearings, valves, plunger guides, governor, cam shaft, etc., the oil under pressure being supplied by two valveless pumps, either of which is sufficient to maintain the working pressure of oil.

The normal output of the engine is 400 brake horse-power, with an allowable overload of 40 horse-power for ½ hour. The exhaust pipe is water jacketed, each section being supplied from the small pump shown at the end of the cross section.

Double ignition is provided for an emergency, by two high tension magnetos, each of which is connected to a separate set of plugs. When starting the engine, an ordinary spark coil and storage battery are used until the engine gets up to speed, when the coil is cut out and the magneto is thrown in.

(47) The “V” Type Motor.

An example of the “V” type motor is shown by Fig. 22, which is a front elevation of the Frontier aeronautic motor, a type that occupies a minimum of space with a minimum of weight.

The cylinders are cast separately and are furnished either with iron or copper water jackets, the copper jackets being deposited over the cylinder barrels by an electrolytic process in much the same way as that of the celebrated French Antoinette. Bolts passing through flanges on the bottom of the cylinder fasten them to the base. A special aluminum alloy is used for the base which is cast in a single piece with webs to receive the bearings. A unit crank-case insures perfect alignment, prevents a greater part of the oil leakage, and forms a much stronger construction than the usual split pattern. A chamber is provided for the cam shaft at the apex of the case through which issue the push-rods. Shafts and piston pins are hollow. All push rods are adjustable for wear and have steel balls running on the cams which eliminate the possibility of mis-timing through wear.

Lubrication is by a bronze pump geared from the crank-shaft and is connected to an oil tank located in the base from which the oil is forced through the crank-shaft up through the hollow connecting rods to the piston pins, thence to the cylinder walls, the surplus returning to the tank in which the strainer is located.

The circulating pump is driven from the cam shaft as shown in the cut and supplies the cylinders and radiator with water through the copper water manifolds which are designed to give an equal supply to each cylinder. Exhaust manifolds are of seamless steel tubing.

The cylinders are 4⅛ bore × 4⅜ stroke, and develop 60 to 70 horse-power at 1,100 revolutions per minute, which speed has been attained with an 8-foot 6-inch propeller having a pitch of 5 feet. Without radiator or propeller, the iron jacketed motor weighs 312 pounds, and copper jacketed weighs 290 pounds, the latter making a difference of 22 pounds in the weight.

A high tension Bosch magneto is used which is mounted on a pad cast on the top of the crank-case and is driven from a gear meshing with the cam shaft gear. Connection is made from the magneto to plugs placed over the inlet valves in the valve caps.

A 100 horse-power aero engine of the “V” type is shown by Figs. 23–24–25, which is built by the All British Engine Company for the aeronautical branch of the English War Department. It has eight cylinders of 5 inch bore, by 4¼ inch stroke, and develops its rated horse-power at 1,200 revolutions per minute. _Data from “Aero,” London._

The crankshaft, which is of three per cent nickel chrome steel, having an ultimate tensile strength of 157,000 lbs. per sq. in., is of distinctly large diameter, and is carried in plain bearings lined with white metal. It is provided with four throws, each crank pin being arranged to take the big end bearings of two connecting rods from cylinders on opposite sides of the crank case. There is a bearing between each throw, and in order to reduce the overall length of the engine the cylinders are staggered on the crank case. The H section connecting rods are stamped out of steel having a tensile strength of 90,000 lbs. per sq. in., and for the purpose of lubrication a hole is drilled from end to end down the center of the web. As mentioned before, the cylinders are staggered, and there is no overhanging of the big end bearings at the point of attachment to the connecting rod. The bearings themselves are lined with white metal. The small end bearings are provided with phosphor bronze bushes, and the piston pin is of steel bored out hollow and hardened.

A very interesting detail of the engine is the combination of the water outlet pipe from the top of the cylinder with the bearings for the rocking arms (which are steel stampings) actuating the valves. This is shown in Fig. 25. A hollow steel column is bolted to the top of the cylinder and protrudes from the water jacket, which is fastened to it with the usual shrunk ring. To this column is attached a hollow T shaped pipe of phosphor bronze, the column of the T piece forming the outlet for the water. On one arm of the T piece the exhaust rocker takes its bearing and on the other the inlet rocker. Each T piece arm is connected to its fellow on the next cylinder by means of rubber pip.

A small bracket projecting from the T piece forms a saddle on which the valve spring rests. This is a plain semi-elliptical leaf spring which works both valves. It is slotted at each end and slightly turned up so as to engage with a cotter pin passed through a slot in the end of the valve stem.

The crank case is of rather unusual design, being absolutely circular in section and machined all over. It is practically a tube with flanged portions bolted on to form the ends. Having no horizontal joints, it is strong and easily kept oil tight. Three radial arms, with slight webs and reinforced with steel columns down the center, support each bearing. The crank case is carried by four feet, which are arranged to accommodate three different widths of engine bearer. To the fore end of the crank case is bolted a long conical aluminum nose carrying at its extremity a compound push and pull ball bearing 6 in. in diameter, which supports an extension shaft bolted to the crankshaft by means of a flanged coupling.

At the outer end of this extension is a flange to which the propeller is bolted, but the arrangement is specially devised to make quick detachment possible. The boss of the propeller has a hollow hub and is plate bolted permanently to it by twelve bolts.

The direct nose is interchangeable with a speed reduction gear so that the propeller can be driven at a lower speed than the engine. Fitting this gear nose raises the center line of the propeller-shaft some 5¼ in. The gears are carried on substantial ball bearings, plain bearings being used also in such a way that they take up the load if the ball bearings through any cause should fail. The reduction is by means of silent chains. The arrangement of the gear wheels is plain from the drawing, and it will be noticed that there is no intermediate wheel between the crankshaft pinion and the camshaft wheel, which are of steel and phosphor bronze respectively. A separate gear wheel is provided on the camshaft for driving the magneto. The water and oil pumps are carried low down outside the crank case, and are driven by intermediate wheels at double the engine speed. The shafts are joined together through Oldham couplings, so that it is possible to remove the pumps separately. Both these pumps are of the gear type.

The camshaft is made in one piece with the cams, and is hardened, being drilled out for lightness. It is enclosed in a casing of steel tube, which is practically separate from the crank case, being attached thereto at one end by the timing gear case and at the other by a saddle. The camshaft is carried in six bearings. An interesting point is the fact that the gear wheels are bolted to flanges on the shafts instead of being attached by keys. Carried in the tube directly above the camshaft is a second shaft forming the fulcrum of the rocking arms for the cam rollers. A very interesting point is the provision of an arrangement for lifting the exhaust valves. The little rocking arms carrying the rollers which bear upon the cams are provided with webs, parallel with the camshaft and between it and the shaft carrying the rockers is a third shaft, the sides of which normally just clear the webs of the rocking arms on either side. This shaft is provided with wedge shape pieces along it, so that by sliding it along the wedges lift the rocking arms clear of the cams, and thus, through the tappet rods and rockers, the valves themselves are opened.

Not the least interesting particular of this engine is the thorough way in which the lubrication is carried out. Four of the bolts which attach the caps of the main bearings are prolonged through the bottom of the crank case, and serve to carry a detachable oil sump which holds sufficient oil for a run of six hours. As already mentioned, the oil pump is driven at twice the engine speed, and maintains a pressure of something like 110 pounds per square inch. It delivers directly into a straight steel tube placed along the bottom of the crank case, and from this tube a vertical tubular connection is taken to each of the caps of the main bearings. The crankshaft and crank pins are hollow, and, as in the previous engine, in the hollow portions tubes of a slightly smaller diameter are placed, the tubes being expanded over at the ends, so that closed annular spaces are formed which are used as lubrication leads. The lubricating oil passes through the main bearings into these annular spaces in the shafts, from them to the annular spaces in the crank pins, and so to the big-end bearings. From the big-end bearings it travels up the connecting rods to the gudgeon pins. It is interesting to note at this point that the connecting rods work in slots in the crank case which just allow sufficient clearance for their travel, in order to prevent the flooding of oil into the cylinders. A steel-lined oil lead is taken up to the saddle which supports the tubular camshaft casing at the propeller end of the crank case. The bearings carrying the camshaft are cut away at their lower edges clear of the tube so that the oil can flow along the full length of the casing, the level being sufficient to allow the cams to dip. Precautions are taken to keep oil from flowing out of the bearings, and the casing over the gears is specially arranged to prevent the oil from flooding below.

(48) Mesta Gas Engines.

The Mesta four stroke cycle, double acting gas engine, built by the Mesta Machine Co., Pittsburgh, is an excellent example of American big engine practice. Mesta engines are built in sizes from 400 horse-power up to the largest used, and is built either in tandem or twin tandem units. While the engine does not differ widely in either principle or construction from engines of the same size it has several features worthy of note that are not found on other engines.

Up to the medium sizes, the cylinders are cast in one piece, the largest cylinders being made in two parts of cast steel with air furnace iron bushings. The central part of the cylinder is open as will be seen from the cuts, and is covered with a cast iron split band bolted at the center line. The valve chambers are located directly opposite one another on a vertical center line, the inlet valve being at the top and the exhaust valve at the bottom. This arrangement gives a better distribution of the mixture, increases the output with given size of cylinder and equalizes the stresses occasioned by the explosions. As the engine is double acting in all cases there is one inlet and one exhaust at each end of the cylinder.

Both the inlet valve and the corresponding exhaust valve on each end of the cylinder are operated by a single eccentric on the horizontal lay-shaft shown running below and parallel to the cylinders. The regulating valves which are controlled by the action of the governor are perfectly balanced against the pressure in the cylinder which results in a very small resistance to the governor action, therefore no oil relay nor similar complications are required. Any of these valves are easily removed for clearing, a point of great importance when running on a gas that is laden with tar or other impurities.

The chrome-vanadium piston rod carries the pistons floating free from the cylinder walls reducing the wear on the bore, while the piston rings maintain a gas tight contact with the cylinder walls. Each piston rod is made in two halves, the joint between the sections being made between the cylinders at which point the rods are supported by an intermediate cross-head and guide. Both parts of the rod are interchangeable. The pistons are made in one casting. As will be seen from the accompanying cuts the front end of the piston rod is carried by a cross-head which relieves the pressure on the piston and packing glands.

Speed regulation is performed by the governor by controlling both the quantity and the quality of the mixture. Independent valves in the gas and air passages are actuated by the governor according to changes in the load. This method of control combines all of the good features of quantity and quality regulation.

Make and break ignition is used, with the igniter trip gear so designed as to allow all of the igniters to be timed from one lever, or adjusted independently as the case may require. Each combustion chamber is supplied with two igniters, one at the top and one at the bottom, which insures regular and rapid combustion and therefore gives a maximum of efficiency and reliability.

Compressed air is introduced into the cylinders for starting at a period corresponding to the power stroke in normal operation. This is accomplished by cam operated poppet valves located in the air main and check valves in the cylinders. By this system the engine can be started and put on full load in less than one minute.

(49) Knight Sliding Sleeve Motor.

The Knight motor was the first four stroke cycle automobile motor to employ an annular slide valve in place of the usual poppet valve. Its success has led to the development of several other motors of a similar type which follow the construction of the original engine more or less closely. Being free from the slap bang of eight to twelve cam actuated poppet valves which hammer on their seats at the rate of a thousand blows per minute, the Knight motor is free from noise and vibration. Instead of the jumping of a number of small parts, there is only the slow sliding of the sleeves over well lubricated surfaces. They make no noise because they strike nothing and can cause no vibration because they are a perfect sliding fit in their respective cylinders.

Besides insuring noiseless operation, the valves increase the output, efficiency and flexibility of the motor for they are positively driven and are not affected in timing by fluctuations in the speed. The wear of the reciprocating increases the efficiency of the sleeve instead of destroying it. With poppet valves at high speeds, the valves do not seat properly in relation to the crank position owing to the inertia of the valves and to the gradual weakening of the valve springs which delays the closing of the valves. Carbon also gets on the seats of the poppet valves and prevents proper closure. These faults cannot exist with sliding sleeves when they are once set right as they are positively driven through a crank and connecting rod.

At high engine speeds the velocity of the exhaust and inlet gases is very high in the poppet valve type due to the many restrictions and turns in the passages which causes back pressure and a considerable loss of power. With the sliding sleeve type an ideal form of combustion chamber is possible and the passages to and from the chamber are short and direct. Very large port areas with a low gas velocity are also possible. The sleeves are more effectively cooled than the poppet type, being in direct contact with the water cooled walls for their entire length. Because of the large port areas, the cylinders receive a full charge of mixture, and as a result the engine accelerates and gets under way with remarkable ease.

The arrangement of the slide valves, or sleeves, is shown by Fig. 28, which also gives an idea of the cylinder form, and the location of the piston. Fitting the engine cylinder closely, one within the other, are the two sliding valve sleeves, and within the inner sleeve slides the power piston.

Each sleeve has two slots cut in it, one on each side, which form an outlet and inlet for the exhaust and inlet gases respectively. When the slots on the intake side of both the outer and the inner sleeves register, or come opposite to one another, and also opposite to the intake pipe, a charge of gas is drawn into the cylinder. After the explosion has taken place, the sliding motion of the sleeves brings the other two openings, on the exhaust side, opposite to one another, and opposite the exhaust pipe, which allows the burnt gas to escape to the atmosphere through the exhaust manifold.

The sleeves are driven from cranks on the half-time shaft shown at the side of each cut, through the small connecting rods, which gives them a reciprocating motion. Like the cam shaft on a poppet valve motor, the lay shaft runs at half the crank shaft speed, since the engine is of the four-stroke cycle type. The lower ends of the sleeves, to which the connecting rods are fastened, are made thicker than the portion within the cylinder, and are heavily ribbed for strength in the overhang.

The sleeves are of the same composition of cast iron as the cylinder and are provided with oil grooves cut in their outer surfaces for gas packing, and the distribution of oil. Leakage between the inner sleeve, and the cylinder head is prevented by a packing ring, or “junk” ring that is fastened to the bottom of the inwardly projecting cylinder head. The junk ring not only prevents the leakage of gas during the explosion, but it also serves another purpose.

The exhaust ports or slots in the inner sleeve are above the junk ring during the explosion, in which position they are protected from contact with the burning gas. The life of valves is greatly increased by this protection. It will be noted that the entire surface of the sleeves is in contact with water jacketed surfaces, making perfect lubrication and smooth working possible. The two spark plugs for the dual ignition system are shown in the depressed cylinder head.

Complete water jacketing encircles the cylinders, cylinder heads, the circulation area enclosing the plugs and the gas passages so that a uniform heat is maintained the entire length of the piston travel.

The half-time shaft, the magneto, and the water pump are driven by a silent chain from the crank case; this drive being found superior to the gears commonly used for this class of work. The cranks on the half-time shaft are made in one integral piece with the shaft.

Although the piston on the Stoddard-Dayton Knight motor has a stroke of 5½ inches, it is scarcely as much as this considered as friction producing travel, because the inner sleeve in which it rests moves down in the same direction 1⅛ inches.

This distribution of the working stroke to two surfaces reduces the wear on the side of the sleeve caused by the angularity or thrust of the main connecting rod. On the compression stroke, both outer and inner sleeves go up in the same direction as the piston, the inner sleeve moving the faster. On the exhaust stroke and suction stroke the sleeves move in a direction opposite to the direction of the piston, but on these strokes there is very little work performed by the piston and consequently little thrust is produced on the sleeves and walls of the cylinder.

It is a valuable feature to have the sleeves descend with the piston on the working stroke because this is the stroke in which the piston has the greatest amount of side thrust.

The up and down movement of the sleeves is very little compared with that of the piston. A stroke of 5½ inches gives a piston speed of 916 feet per minute at a speed of 1,000 revolutions per minute. The stroke of the sleeves is 1⅛ inches and its speed is but 93.7 feet per minute, or a little more than one-tenth that of the piston. This fact makes the problem of lubrication a feasible one, the slow-movement of the sleeves distributing the oil thoroughly between them as well as between the outer sleeves and the cylinder walls.

The action of the valves, and their position at different points in the cycle, is shown in diagrammatic form by Figs. 28–29–30–31–32–33, the particular event to which each diagram refers being marked at the foot of the cuts. The direction of the sleeve movement is indicated by the arrows at the bottom of the sleeves. Particular attention should be paid to the position of the slots in the sleeves.

The first three diagrams show the position of the inlet slots that govern the admission of the combustible gas from the carburetor. Fig. 28 shows the slots coming together to form an opening in the inlet port as the lower edge of the outer sleeve separates from the upper edge of the inner sleeve. The outer sleeve is now moving rapidly downward while the inner sleeve is slowly rising, and as their motion is opposite the opening is quickly formed. Fig. 29 shows the full opening with the slots in register.

When closing (Fig. 30) the outer sleeve is nearly stationary while the inner sleeve is rising rapidly. When the inner sleeve port is covered by the lower edge of the junk ring, the valve opening is closed, the slot in the outer sleeve remaining opposite the inlet opening.

The exhaust port opens (Fig. 31) when the lower edge of the slot in the inner sleeve leaves the junk ring in the cylinder head, the sleeve moving rapidly downward at the moment of opening. To obtain a rapid opening of the exhaust, the ports are arranged so that the inner sleeve is just about to reach its maximum speed at the time of opening.

The outer sleeve closes the port (Fig. 33), closure starting when the upper edge of the outer sleeve coincides with the lower edge of the cylinder wall port. At this time the outer sleeve is traveling downward at maximum speed, so that the closing of the exhaust is as rapid as the opening.

The lubrication of the Knight motor is accomplished by what is known as the movable dam system, which overcomes the tendency of the motor to over-lubricate. A movable trough is placed under each connecting rod, in the crank case, that is connected to the carburetor throttle lever in such a way that the opening and closing of the throttle raises and lowers the troughs.

When the throttle is opened, raising the troughs, the points on the ends of the connecting rods dip deeper into the oil which creates a splashing of oil on the lower ends of the sliding sleeves. In this way the oil is fed to the engine in direct proportion to the load and the heat produced in the cylinder. When the motor is throttled down, the points barely dip into the oil.

An excess of oil is fed to the troughs by an oil pump, which keeps them constantly overflowing. The overflow is caught in the pumps located in the crank case, and returned to the circulation so that it is used over and over again.

Claims of great efficiency are made for this system, there having been many tests made showing 750 miles per gallon of oil, while even as high as 1,200 miles per gallon has been made under favorable conditions.

The oil pump is contained in the crank case, and is of the gear type, insuring positive action. The pump also acts as a distributer, a slot being cut in one of the gears which register successively with each of the six oil leads. In this way it is possible to obtain the full pump pressure in each lead should they become obstructed in any way.

In the upper half of the crank case are cored passageways through which the air passes before reaching the carburetor. These passages not only eliminate the rushing sound of the intake air, but also form an efficient method of warming the air supplied to the carburetor and cooling the crank-case. It is possible to furnish warm air after the engine has been idle for several hours, as the oil in the crank case remains warm longer than any other part of the engine.

(50) Reeves Slide Sleeve Valve.

A simple and compact form of slide sleeve valve gear has been developed in England that is of more than passing interest. It permits of a maximum area for both the inlet and exhaust gases which of course keeps the velocity and back pressure at a minimum for a given valve lift. The small lift also insures noiseless operation and a small amount of wear. The sleeve is balanced at the end of the working stroke. The combustion chamber is nearly hemispherical in shape which reduces the heat loss to the walls.

Referring to the section of the end of cylinder given in the diagram, (34) A is an open-ended water-jacketed cylinder in which the piston B works. At the upper end of the cylinder is attached a ring C forming an extension of the stationary cylindrical head D carrying the sparking plug. At the lower end of the head D is provided a seating E for the sliding cylindrical inlet valve F, which takes its bearing around the circular head. This inlet valve is provided with expanding rings G to keep it gas-tight. Surrounding the inlet valve F is a second cylindrical exhaust valve H, which is provided with an angular seating at J. The outer circumference of the cylindrical exhaust valve H bears against the walls of the cylinder.

Cast in the cylinder is an annular space K communicating with a passage L for the admission of the inlet gases. These pass through suitable ports cut in the sides of the exhaust valve H and the inlet valve F, so that they are free to pass through the space made when the inlet valve F is lowered from its seat. A similar type of annular space M is cast in the cylinder in connection with an opening O for the passage of the exhaust gas when the cylindrical valve H is raised from its seating at J.

The cylinder head is not water jacketed as the builder states that the continual passage of the intake gases keeps it reasonably cool. The exhaust passages are thoroughly water cooled.

(51) Argyll Single Sleeve Motor.

The Argyll sliding sleeve automobile motor is unique in the fact that only one sleeve is used to control both the inlet and exhaust gases instead of the two sleeves commonly used on the Knight motor. This sleeve, instead of having either a purely vertical or horizontal motion, has a peculiar combination of the two, that is to say, it moves a certain amount in rotation within the cylinder, and an equal amount vertically, the combined motion constituting an ellipse. The external appearance of the engine is shown by Fig. 35, which will give an idea of the general arrangement of the cylinders, ports and piping.

In Fig. 36, is shown the successive movements and events determined by the sleeve, and the method of opening and closing the inlet and exhaust ports by the elliptical movement of the sleeve. The shaded ports are one of the inlet and one of the outlet ports, respectively, which are cast in the cylinder wall, and are afterwards machined true. The dotted port, which changes its position in each diagram, is one of the ports in the moving sleeve, its position in each of the figures is marked by the event that is occurring in the cylinder at that time.

In diagram 1, the shaded port to the right is the exhaust port, and the shaded port to the left, the inlet, this relative arrangement being true, of course, in each of the succeeding diagrams. It will be noted, that in the position shown, in the exhaust stroke (beginning of stroke), the sleeve port has just started on its downward stroke, moving also a trifle to the right as it progresses. Its progress to the right may be more clearly seen by consulting diagram 2, for the movement.

By consulting the other five figures it will be seen that the dotted port, in its relation to the shaded ports, first moves out to the right, and then reverses, moving to the left, and this combined with the up and down movement constitutes an elliptical path. In diagram 6 the exhaust is closed, and the inlet port has just begun to open, the dotted port now starting to move out to the left, and to rise.

In diagram 10, the inlet is nearly closed, the sleeve port passing away from the cylinder ports to the water jacketed portion of the cylinder above.

This series of diagrams shows the operation of the duplicated port of the sleeve (which port is the one shown dotted) in relation with one of the inlet ports and one of the exhaust ports in the cylinder wall, the latter ports being marked respectively I and E. The elliptical movement referred to in the text can be traced by following the different positions of the dotted port in the sleeve. In the top row of diagrams it is seen to come downwards and also to move over to the left, whilst in the lower set it rises—bearing still to the left—until, after Fig. 10, it goes higher up for the compression and explosion strokes, during which it bears over to the right and comes down again ready to commence once more the cycle, as in Fig. 1. The other ports in the cylinder wall are the same as those shown, and the other ports in the sleeve are akin in shape to half of the dotted port, but they are without the little tongue cut in the base of this double purpose port. This little tongue in the duplicated port is designed to give as much lead to the exhaust opening as possible, without interfering with the correct timing of the inlet port. The way in which it just misses interfering with the closing of the inlet port is seen in Fig. 10. We are indebted to “The Motor” for these cuts.

(53) Sturtevant Aeronautical Motor.

The cylinders of the Sturtevant aeronautical motor are of the “L” type and are cast separately with the cylinder barrel and water jacket in one integral casting. A special iron is used for these castings that has an ultimate tensile strength of 40,000 pounds per square inch. The valves which are easily accessible through valve covers, are operated directly from the cam shaft without valve rockers. A hollow cam shaft is used with integral cams to insure a maximum of strength with a minimum of weight, and bearings are placed between each set of cams. A bronze gear fitted on the cam shaft meshes with a gear on the crank shaft without intermediate idlers.

Like the cam shaft, the crank is bored out from end to end with a propeller flange applied on a taper at one end of the shaft. A bearing is provided between each throw with an additional thrust bearing at the forward end of the shaft which may be arranged to take either the thrust or the pull of the propeller. Lubricating oil is applied to all the bearings under a pressure of twenty pounds per square inch, this pressure being maintained by a gear pump attached directly to the end of the cam shaft. The oil is transferred from the pump to the bearings through passages cast in the base, no piping being used. Oil enters the hollow crank shaft at the main bearings and is conducted through the arms to the connecting rod bearings. The oil flying from the crank shaft falls into the oil sump at the bottom of the case where it is cooled before being used again. A second gear pump in tandem with the first takes the oil from the sump and forces it through a filter into the tank.

This system enables the use of a more efficient filter than with the suction type and eliminates any danger of its becoming clogged and stopping the oil supply, since, in the event of such an occurrence the pump would furnish sufficient pressure to burst the filter. However, the filter is particularly accessible and may be instantly removed for cleaning without disturbing the oil. The tank regularly fitted to the motor holds sufficient oil for three hours’ use. If the engine is required to operate for a longer time without opportunity for replenishing the oil supply, a larger tank can be used. As no oil is allowed to accumulate in the base with this system of lubrication, the motor can be operated continuously at an angle.

Water circulation is maintained by a centrifugal pump of large capacity, the impeller of which is mounted directly on an extension of the crank shaft, eliminating the usual bearings and its grease cup.

The ignition is provided by a high-tension Mea magneto, its special construction permitting the motor to be started under a retarded spark avoiding the danger of back kick from the propeller.

The cylinder and all exposed parts are rendered absolutely weather-proof by means of a heavy coat of nickel plating.

(54) The Rotating Cylinder Motor.

While it is the common belief that the rotary cylinder gasoline motor is of French origin it may safely be said that this type of motor was in actual use in America for several years before it even reached the experimental stage in Europe. The Adams-Farwell Company of Dubuque, Iowa, were driving automobiles successfully with a rotary cylinder motor before Orville Wright flew at Fort Meyer, Va. Although the original Farwell motor more than proved its right to existence by faithful service under the most exacting conditions, the motor never received the consideration that it deserved, probably because of its great divergence from what is known as “accepted practice.”

In Europe no such prejudice existed, and consequently the type made rapid strides, although, to the writer’s belief, the European model is inferior in many ways to the original American type. The fact that this type of motor holds practically all of the world’s aviation records speaks for its practicability in spite of its unusual construction.

With the rotary motor, the cylinders and crank case revolve about a stationary crank shaft, the latter part not only serving as a point of reaction of the cylinders but as a support and intake pipe as well. Since the crank throw remains stationary, the cylinders and pistons revolve about two different centers, the cylinders revolving about the crank case and the pistons and connecting rods about the crank pin. Since the pistons, cylinders, and connecting rods must necessarily revolve together, as one unit, there is absolutely no reciprocating motion in regard to the crank shaft except for a very slight movement due to the difference in angularity of the connecting rods. The motion of all the parts is strictly rotary in every sense, except for the relation of the pistons to the cylinders, and the motion is as continuous as in a turbine. This insures freedom from vibration. As the cylinders and crank case have considerable inertia there is no need of the added weight of a fly-wheel. The movement of the piston in the cylinder bore is brought about by the difference in the centers about which these parts revolve. This gives cylinder displacement without the reversal of stresses or shock or jar.

Because of the revolving cylinders, the mixture is supplied to the crank case through a hollow shaft, the gas being drawn into the cylinder on the suction stroke through an inlet valve placed in the head of the piston. As a rule, the exhaust is direct to the air through the exhaust valves and without manifolds or mufflers. The motion of the cylinders through the air multiplies the efficiency of the radiating Fins.

(55) The Gyro Rotary Motor.

In the Gyro motor, made by the Gyro Motor Company of Washington, D. C., are embodied all of the principles of the typical revolving motor, but with extensive improvements in the design and in the details. It weighs 3¼ pounds per horse-power, complete. This light weight is due to the design of the motor and to the use of alloy steels, and is attained without sacrificing strength or durability.

Each cylinder is machined out of a heavy 3½ per cent tubular nickle steel forging that weighs nearly 40 pounds. After the metal is removed and the cylinder worked down to size, the shell weighs but 6½ pounds. The radiating ribs on the outside of the cylinder are machined out of the solid bar, and are arranged in helicoid or screw-like formation around the cylinder barrel. This adds to the strength of the cylinder and also aids in the circulation of the air. The comparative thickness of the cylinder wall may be seen from Fig. 44. The stiffening effect of the radiating ribs will also be noted. The crank case to which the cylinders are fastened is of vanadium steel, and is divided into two parts. In addition to supporting the cylinders, the crank case also serves as a mixing chamber for the gasoline and air. By removing the bolts seen between each cylinder, the entire working mechanism can be laid bare for inspection. The exterior of the case carries the exhaust valve mechanism and the ignition distributer. The crank shaft is a nickel steel forging with an elastic limit of 110,000 pounds. It is bored hollow throughout its length and serves as an intake manifold by conveying the mixture from the carbureter, attached to its outer end, to the crank case.

The intake valves in the heads of the piston are mechanically operated by a specially patented movement which consists of two parts, a counter-balancing member, and an operating member. The counter balance balances the valve against the disturbing influence of the centrifugal force, while the operating member, which is fastened to the connecting rod, controls the opening or closing of the valve by the angular position of the connecting rod. This valve action insures a full opening of the valve and a full charge during practically all of the suction stroke.

There are two separate paths provided for the exhaust gases, one being through the auxiliary exhaust ports at the end of the stroke, and the other path through the exhaust valve located in the cylinder head. The auxiliary ports may be seen in the cross-section directly below the piston head in cylinders 4 and 5. The auxiliary ports are uncovered by the piston at the inner end of the working stroke, and it is at this point that the greater percentage of the exhaust leaves the cylinder. These ports or holes are formed on a projecting annular ring in which enough material is provided to make up for the strength lost by boring the ports. As these ports are, in the majority of cases, bored at an acute angle with the center line of the cylinder, it is impossible for the cylinder oil to escape.

All exhaust valves are operated by levers and push rods connected to a cam mechanism on the outside of the crank case. A single cam ring operates all of the valves except where a step-by-step compression is desired. The exhaust mechanism is provided with a simple device by which the closing of the exhaust valve may be delayed through any portion of the exhaust stroke, thus reducing the compression and adding to the facility of cranking. The motor is started with the compression entirely released in which condition it can be spun about its shaft with ease.

After giving the motor its initial spin, the compression and spark are thrown in and the engine begins its normal operation. The compression release lever may be used for starting or slow running and in cutting off the power regardless of the ignition advance or retard.

One connecting rod, called the “master” rod, is an integral part of the spider that contains the ball bearings of the crank pin, thus controlling the angular relation between the connecting rods and cylinders. The remaining six rods are, of course, articulated on the spider by pins so that the rods may move in regard to the spider when in different parts of the stroke. The shell of the pistons is of a fine grade of iron, very thin and elastic, so that it may conform readily to the outline of the cylinder bore. The head of the piston consists principally of the intake valve cage, the cage carrying the piston pin as well as the valve.

Oil is supplied by a positive pump that measures the lubricant in exact proportion to the load on the engine. Both the oil and the gasoline mixture enter the crank case through the hollow crank shaft and mingle in the form of a vapor. This oil mist reaches every moving part and results in perfect lubrication. The pistons are provided with oil shields which carry the oil directly to the cylinder walls and prevent the loss of oil through the exhaust valve.

Ignition is performed by a high tension magneto through a distributer which directs the current to the proper cylinder. As in all rotary engines, the Gyro has an uneven number of cylinders (3, 5, and 7) in order that the cylinders receive firing impulses through equal angles of rotation. An even distribution of firing is impossible with an even number of cylinders, as two adjacent cylinders out of six alternately fire together and then 180° apart. This produces a very jerky turning movement, and is productive of much vibration. In the seven cylinder motor the magneto is driven by gears having a ratio of 4 to 7, and the high tension current is distributed to the cylinders by 7 brushes, the leads from the brushes being taken direct to the spark plugs.

(56) Gnome Rotary Motor.

The Gnome was the first rotary aviation motor built in Europe and is still one of the most capable flight motors abroad as its many victories and records prove. It is built in four sizes, 50, 70, 100, and 140 horse-power, the 50 and 70 horse-power motors having 7 cylinders, and the 100 and 140 horsepower, having 14 cylinders, which consist of two rows of 7 cylinders per row. The cylinders of all sizes rotate about a stationary crank shaft while the pistons rotate in a circle, the center of which is the crank pin. Vibration is practically eliminated at high speed as the pistons do not reciprocate in the ordinary sense of the word, but simply revolve in a circle, the reciprocating relation between the cylinders and pistons being obtained by the difference in the centers of the two revolving systems. The cooling effect of the radiating ribs is greatly increased by the air circulation set up by the rotation of the cylinders. This method of cooling introduces a great loss of power due to the blower action of the cooling ribs, this loss often amounting to 15 per cent of the output of the engine.

The crank shaft is stationary and acts as a support for the engine, one end being fastened into a supporting spider which forms a part of the aeroplane frame. The crank shaft is hollow and also serves to conduct the mixture from the carburetor fastened at its outer end to the crank-case of the motor. Only one crank throw is provided on the seven cylinder engine as the cylinders are all arranged in one plane which passes through the center of the crank throw. In the fourteen cylinder engine where the cylinders are in two rows, there are two crank throws, one for each row of cylinders.

The seven cylinders are arranged radially, as will be seen in Fig. 50, each being spaced at an equal distance from the crank shaft and at equal angles with one another, the arrangement in general being similar to that of the “Gyro” motor shown in the preceding section. All cylinders are turned out of solid forged steel bars, the cylinder walls being only 1.2 millimeters thick after the machining operation. This results in the strongest and lightest cylinder possible to build, as all superfluous material is removed and the chances of defects in the material are reduced to a minimum as the character of the metal is revealed by the extended machining operations.

As the motor operates on the four stroke cycle system, an odd number of cylinders is chosen in order that the firing may be carried out through equal angles in the revolution to obtain a uniform turning movement. Since a four stroke motor must complete two revolutions before all of the cylinders have fired, or completed their routine of events, it is evident that the number of cylinders must be odd in order to bring the last cylinder into firing position in the last revolution. When seven cylinders are used, the cylinder are fired alternately as they pass a given fixed point, that is, one cylinder is fired, the next skipped, the third fired, and the fourth skipped, and so on around the circle, so that the firing order in terms of the cylinder numbers is 1, 3, 5, 7, 2, 4, 6. The cylinders fired in the first revolution in order are 1, 3, 5, 7, and in the second revolution, 7, 2, 4, 6, the cylinder 7 being common to both revolutions. The cylinders are numbered according to their position on the engine, and =NOT= according to the firing sequence. See Fig. 51.

With a six cylinder engine it is possible to fire the cylinders in two ways, the first being in direct rotation; 1, 2, 3, 4, 5, 6 thus obtaining, six impulses in the first revolution, and none in the second. The second method is to fire them alternately, 1, 3, 5, 2, 4, 6, in which case the engine will have turned through equal angles between impulses 1 and 3, and 3 and 5, but through a greater angle between 5 and 2, and even again between 2 and 4, and 4 and 6. See Fig. 52.

Mixture is drawn into the cylinder by the suction of the piston through an inlet valve in the piston head, in practically the same way as in the “Gyro” motor, but unlike the latter motor, the valve is lifted by the suction (automatic valve) and not by the mechanical actuation of the connecting rod. The inlet valve is balanced against the effects of centrifugal force by a small counter-weight in the piston head, and the valve is held normally on its seat by a flat spring acting on the valve stem. The gases are brought into the crank case from the carburetor through the hollow crank-shaft as described elsewhere. See Fig. 53.

All exhaust valves are located in the cylinder head and are actuated by long push rods that are moved by individual cams in an extension of the crank case. The exhaust valves are counter-balanced against centrifugal force and are retained on their seats by a flat spring. The counter weights do not entirely overcome the effects of the centrifugal force but allow a slight excess to exist which will permit the engine to run with a broken spring. All of the exhaust gases escape directly to the atmosphere without piping or mufflers.

Owing to the fact that the advancing or leading face of the cylinder is cooler than the trailing face, the cylinder bore is thrown out of line by the difference in expansion between the two sides. Because of this distortion of the bore, a special form of piston ring is used, which, by its flexibility, adapts itself to variations in the bore. These rings are of brass and are shaped like the pump leathers of a water pump so that the pressure of the explosion acting on the inside of the ring tends to force the thin shell against the cylinder. In spite of this precaution, the compression pressure is very low at the best, in the most of cases not over 45 pounds per square inch. The exhaust valve screws into the end of the cylinder and may be removed, complete with its seat, for the frequent regrinding necessary to efficient operation. After the cylinders are ground with the greatest care and accuracy, the finishing is carried still further by wearing-in the cylinder with an actual piston carrying an “obturateur” or piston ring.

The bushing into which the spark plug screws is not integral with the cylinder as in a cast construction, but is welded into the side of the cylinder head by means of the autogenous process. It is also evident that this construction enables the inlet valves to be easily removed, since these screw into the piston head. Both inlet and exhaust valves in the Gnome engine are removed with the greatest ease, special socket wrenches being supplied for the purpose. The castor oil, which is used as a lubricant, and the gasoline, are fed by a positive acting piston pump to the hollow crank shaft. The lubricant and fuel then pass through the automatic inlet valve in the head of the cylinder.

The spark produced by the high tension magneto is led to the proper cylinder through a brush that presses on a revolving ring of insulating material in which is imbedded 7 metallic segments, one of the segments being connected to a corresponding cylinder. As the distributor ring revolves the segments come into contact with the brush in the proper order. The magneto is stationary and is supported by a bracket in an inverted position. A pinion on the magneto shaft meshes with a large gear mounted on the revolving crank case so that the armature of the magneto always bears a positive relation to the piston position. As the engine requires seven sparks for every two revolutions, or 3½ sparks per revolution it is evident that the magneto must turn 1.75 times as fast as the engine, if the magneto is of the ordinary type that generates two sparks per revolution. In other words the magneto speed is to the engine speed as 7 is to 4.

The arrangement of connecting rods is interesting, the big end of one rod being formed into a cage for the reception of the crank-pin ball race. The outer circumference of the cage carries the pins to which the other six connecting rods are fastened. It is necessary that one rod be integral with the cage to prevent its rotation in regard to the cylinders. Annular ball bearings are used on both the main bearings, for the thrust bearing to take the thrust of the propeller, and on the large end of the master connecting rod. The large ends of the auxiliary connecting rods and the small ends of all the rods have plain bearings.