CHAPTER IXTHE MOTOR

This is a subject so vast and comprehensive, that it will require most careful thought and attention in order to get a working idea of the principle. The greatest refinements are resorted to in the building and handling of engines, and more attention is bestowed on this part of the automobile than on any other feature for the following reason:

Value of Fuel Utilized.—Not more than eighteen per cent. of the value of the fuel is actually utilized. The rest is waste. A gasoline engine is a heat motor,—that is, it derives its power from the expansion of the fuel, and this expansion is produced by the heat.

Now the loss referred to comes about in this way: About 52 per cent. of the loss is taken up by the water which surrounds the engine cylinders; from sixteen to seventeen per cent. escapes at the exhaust; and fifteen per cent. loss is due to conduction and radiation.

The Waste.—The great waste, therefore, liesin the cooling means, which must be employed. The temperature of the ignited gases reaches fully 2200 degrees, which is over ten times the temperature required to convert water into steam.

Water absorbs more heat than any other substance, so that this quality is utilized; but the water, if not kept in motion, when applied to such a highly-heated surface as an engine cylinder, would be converted into superheated steam, and would then be of no further value.

Water Absorption.—This necessitates a constant and intermitting motion, so that the more rapidly the water moves, the less it will become heated. At the same time, means must be provided to cool the water in its circuit back to the engine, and the most efficient means to accomplish this is to provide a radiator at the forward end of the machine.

The circulating system, together with the radiator, will be described under their proper headings.

Engine Types.—There are two distinct types of engine, one called thetwo-cycle, and the other thefour-cycle.Cyclehas reference to a period or turn, in which certain mechanical operations are completed in regular order so to form a succession of events.

The Four-Cycle Engine.—These events in a four-cycle engine require the crank to make twocomplete turns, the order being as follows: Starting with the explosion of the charge, the first element in the cycle, is the downward movement of the piston (expansion); second, the return of the piston to the upper end of the cylinder (exhaust); third, the downward movement of the piston, on its second revolution, and the drawing in of a fresh charge of fuel (suction); and fourth, the return stroke which compresses the fuel for driving the piston down the next stroke (compression).

The Two-Cycle.—The two-cycle engine, at the explosion, sends the piston downwardly, and as the crank case and cylinder are connected up together so as to form an air tight receptacle, within which the crank and shaft turn, the downward movement of the piston compresses all the gas which has been previously drawn into the crank case.

When the piston reaches the extreme limit of its downward movement, it uncovers a port in the side wall of the cylinder, so as to afford an outlet for the gases of combustion, and immediately thereafter the piston also uncovers a duct that leads from the crank case, so that the previously compressed gases, as stated, rush in, and this inward movement of the fresh gas, also facilitatesthe movement of the burnt gases at the opposite side.

Compression.—When the piston starts on its return stroke, or upward movement, it compresses the charge thus received, and when the piston nears the upper end of its stroke the sparking mechanism again explodes it, so that the cycle is formed by the two operations, performed by a single turn of the crank shaft.

This latter type of engine is not used to a great extent. It has the advantage that no valves are used, except the one at the inlet of the gas to the crank case, and no stems, push rods, cam shafts, or springs are required to control the movements of the fresh and burnt gases. Aside from that such engines weigh considerably less than the four cycle type.

Economy of Four-Cycle Engine.—On the other hand, the four cycle is more economical, because there is more time for the admission of the fuel, and for exhausting the gases. Furthermore, it is obvious that in a two cycle engine more or less of the fresh fuel gas is mixed with and is discharged from the cylinder with the burnt gases.

As the discharge of the burnt gases and the admission of a fresh charge, is practically simultaneous, the opening of the discharge is placed in thecylinder at such a point that the pressure of the gases cannot be utilized for the full downward stroke, as is the case with the four cycle type.

THE FOUR-CYCLE ENGINEFig. 63. Firing Position.Fig. 64. Return First Cycle.

THE FOUR-CYCLE ENGINE

Fig. 63. Firing Position.

Fig. 64. Return First Cycle.

Valve Movements.—Before proceeding to explain the engine in detail, the different valve movements of a four cycle cylinder are shown, and this will be of service in explaining the different parts as they are referred to.

In the construction of engines, as will be more particularly pointed out hereinafter, the inlet andexhaust valves are usually operated by mechanical means, but certain engines are so constructed that the inlet valve is automatic in its operation, and the exhaust valve only is actuated mechanically.

In the drawings, Figs. 63 to 66, inclusive, both valves are operated from cams on a secondary shaft, and in the first of these four figures the crank has just turned the point where the piston is at its highest limit, and is about to descend. Both valves A B are closed, and the spark fires the charge, driving down the piston to its lowest limit.

In Fig. 64 the crank is shown about to move the piston upwardly, and just as it turns the dead center the cam C, on the secondary shaft, unseats the valve B, through the stem D. As the piston moves upwardly, the burnt gases are forced out past the valve B.

When the piston reaches the highest point in its first revolution, as shown in Fig. 65, the stem D drops off the cam C, thus closing the discharge, and immediately the valve A is opened by the cam E moving the valve stem F upwardly, and as the piston now descends, fuel is now drawn in until the piston reaches its lowest point.

In Fig. 66 the crank is turning the dead center, and is about to move upwardly, and the cams G E are now both in such position that the valves A B are closed, and when the piston moves up again,to complete the second revolution, the fuel gas within the cylinder is compressed, and ready to be fired the moment the crank reaches the position, shown in Fig. 63.

Fig. 65. Drawing in Charge.Fig. 66. Compression.

Fig. 65. Drawing in Charge.

Fig. 66. Compression.

The Ignition Point in the Cycle.—In practice, the firing takes place before the crank has made the turn past the dead center, and this is calledpre-ignition, when the spark is advanced too far to the left. The ignition should take place slightly before the crank turns, because it takes a small interval of time for the charge to burn the gases, and during this time the crank will havepassed the dead center, and started on its way downwardly.

From the diagrams it will be observed that two of the strokes, namely the first and the third, are downward, and the second and fourth are upward, and that the downward strokes take place during the admission and impulse, and the compression and exhaust while the piston moves upwardly.

The Fly-Wheel.—As the impulse in this type can take place only at each second revolution, it is obvious that some means must be provided to keep the shaft moving during the two turns, and for this purpose the fly-wheel is utilized.

Practice has found the multi-cylinder type the most valuable, in connection with the fly-wheel, as in employing two or more cylinders in line, a smaller fly wheel will be sufficient.

Impulses in 4-Cylinder Engine.—In such a case the four cylinders are arranged so the impulse will be at four different points of the shaft, and we may assume that the four cylinders in Figs. 63, 64, 65 and 66, show the relative positions of the four pistons in a four cylinder engine.

The Cylinder Case, and Connections.—A cross section of a case and the relative positions of the various parts, is shown in Fig. 67. The cylinder A is provided with a water jacket B, so as to form a space C around the cylinder which has an inletpipe D at the bottom, and an outlet pipe E at the upper end.

Fig. 67. Automatic Inlet Valve.

The inlet valve F is in the head of the cylinder, and it is held against its seat by a tension spring G. The exhaust valve H is placed in a lateral extension of the cylinder, in such a position that it is directly above the secondary shaft I running through the crank case. The stem J of the valve, is actuated by a cam K on the secondary shaft, and it is, preferably, made in two parts, the upper being so arranged that it has a limited longitudinalmovement independently of the lower part, and a spring is arranged so as to provide for longitudinal thrust in either direction.

The crank shaft M has alongside the crank, a gear wheel N, which meshes with a gear O on the secondary shaft I, this latter gear being twice the diameter of the gear N.

Piston and Crank Construction.—The piston is hollow, and the crank is located as close to the head as possible. This has two or more circumferential grooves, to receive packing rings. The rings are made of very hard steel, and are turned up slightly larger than the diameter of the cylinder, and then cut across diagonally, so they may be sprung into place, and when in position they will bear against the inside of the cylinder, and thus serve to prevent the passage of the gases.

Calculating the Efficiency.—The great problem with every beginner is to know something of the power of the engine, and how it is determined. Considering that the boy knows nothing of the terms used to designate the step we shall try to make the following description as free from technicalities as possible.

In Fig. 68 a cylinder is represented, containing a piston A. B C indicate the limits of the stroke, and for convenience this space is provided with eleven marks to represent the pressure of the ignitedgases at various portions of the travel of the piston.

Pressure in Explosion.—When the explosion takes place, at B, the pressure will be, approximately, 230 pounds per square inch of the piston. When it moves to the next mark the pressure has decreased to 220 pounds, at the next mark it is 200, and so on, until, at the end of the stroke, opposite C, the pressure is only 40 pounds.

Fig. 68. Calculating Efficiency.

Expansion Line.—These figures represent theexpansionline. It is now necessary to get themean effective pressure, which means that we must know what the average pressure of the gas is in each square inch from B to C.

Mean Effective Pressure.—This is obtained by adding together the figures given in the sketch, and the result is, 1530. As eleven pressures were required to produce this sum, it should be divided by that number, making the result 148, avoiding fractions, as we shall do in all the calculations.

The figures represent that the mean effective pressure of the gases on the piston is 148 pounds. If this is multiplied by the area of the piston, and this result by the stroke in feet and the number of power strokes per minute, we get what is calledfoot pounds.

Foot Pounds.—Assuming that the diameter of the piston is 5 inches, which, figure, if multiplied by 3.1416, will give its area as a little over 15-1/2 square inches. Let us assume the crank is 4 inches. This will give a power stroke of 8 inches.

To find out how many power strokes there are in a minute, we must know the revolutions, and this being taken at 800, and a power stroke at only every other revolution, would mean that we have 400 impulses, and each impulse traveled 8 inches, = 3200.

This represents inches, which must be converted into feet, so that we have 266 feet of power strokes per minute.

First multiply the mean effective pressure on the cylinder, that is 148 × 15-1/2, which equals 2294. Then, 2294 × 266, equals 610,204. This product representsfoot pounds.

Work or Energy.—A foot pound is the amount of work or energy expended in raising a weight of one pound, through a distance of one foot. If 550 pounds should be raised one foot in one secondof time it would represent one horse power of work accomplished. If 550 pounds should be raised one foot in one minute of time it would be equal to 550 × 60 = 33,000 foot pounds, and this would mean one horse power, or the work done in one minute of time.

Fig. 69. Two-cycle Expansion Position.

In our above calculation we have determined how many foot pounds we had in a minute of time, so that if we divide the foot pounds 610,204, by 33,000, we shall get as a result, a little over 18-1/2 horse power.

The Two-Cycle Engine.—The longitudinal shell A, Fig. 69, is separate from the crank case B, the latter being secured to the former by flanges and bolts, as at C. The piston D is of such length that when it reaches the limit of its compression stroke, as shown in this figure, it covers both the supply port E and the discharge port F.

In its outward stroke the upper end clears both of these ports as in Fig. 71, the discharge port F being the first to open, as shown in Fig. 70.

Fig. 70. Exhausting.

Fig. 71. Compression.

Cycle of Operations.—The cycle of operation is as follows: The inward stroke, which is in the direction of the head of the cylinder, draws in the gaseous fuel through the valve G, and at its outward stroke the gas in the crank case B is compressed, and the moment the end of the pistonpasses the inlet port E, the gas passes through the duct H into the cylinder above the piston.

The burnt gases within the cylinder pass out the discharge port F, facilitated, in a measure, by the compressed inflowing gas. When the piston again returns, and passes the discharge port, the gas is trapped, and is compressed during the inward stroke of the piston.

The Crank Shaft.—The most important element in the engine is the crank shaft. It is usually made of a single steel forging, and out of this are turned up the crank wrists, the crank arms, and the bearings which are placed intermediate the different cranks. It is made extremely large to provide for any strain due to the fuel explosions, and it is the most difficult part of the engine to turn out.

Fig. 72. Crank Shaft.

Special Metals.—Special metals are used by various manufacturers, and the sizes and structural shapes are now so well understood that few of them break, although in the early history of theengine this was the weak and troublesome part of the car.

Improper alining, in the case, and poor or faulty bearings, were responsible for many accidents, and now means have been found to overcome most of these objections.

Engine Troubles.—When we come to consider the engine troubles, so-called, we shall find there are legions of them. In these days many of the troubles are easy to remedy, but to remedy them means that the causes of troubles should be understood. A physician cannot prescribe for a disease until he has made a diagnosis.

Sometimes the difficulty will be recognized by the symptoms, and is easily adjusted. But suppose the firing is all right, and the engine fails to pick up, and seems to be dying out, it may be attributable to several causes, either one of which would account for it.

Difficulties Pointed Out.—If the engine seems to run down, and fails to pick up quickly, it may be due to water in the carbureter, or to a weak battery, or to leaks in the water jacket that will admit water into the compression chamber, or the trouble may be faulty compression.

Other things should be looked up: The pump may be out of order, the connections loose, and thus permit waste through the leaks, or there maybe a stoppage somewhere in the water circulation, or the water may be exhausted, or the gasoline too low or too poor for the kind of carbureter which you have.

If anything is due to the engine itself, in the vast majority of cases, it is due to poor compression. The engine is too often blamed for faults which belong elsewhere. Nevertheless, it is well carefully to examine the bearings, to look over the clutch, and the bearings in the line leading to the drive shaft.

Starting the Engine.—In starting, some engines give a great deal of trouble, usually due to wrong adjustment of the sparking device. This should not be advanced too much. If the trouble is not at that point, it may arise from too weak a suction, or an obstruction in the carbureter itself.

Carbureter.—At slow turning speed of the engine, the carbureter is very sluggish, because it must be started up from a condition of repose, and unless there is the best of compression, the suction will not be sufficient to dislodge or move the slightest impediment which may be in the way.

Low Compression.—Low compression arises from numerous causes. A carelessly screwed sparking plug; defective or partly blown out gasket in the cylinder head; loose, or partly open compression cock; a sticking valve; a rusted, ordefective inlet valve; leak in the combustion chamber; or a worn or scratched cylinder.

Whenever it is possible, the engine should be examined to observe the condition of the piston rings. Sometimes the rings will break into small pieces, and these parts will wear the most perceptible creases in the cylinder walls. When such is the case they will have to be taken out and lapped.

Mixtures.—Too rich a mixture has the effect, in many cases, of causing a deposit of carbon which is bad for the engine. It coats the walls of the cylinders, and is hard to remove. The application of petroleum and alcohol, if allowed to remain in the cylinder for some hours, will aid in taking it out, but removing the cylinder and scraping is the only safe method.

The usual way to test the cylinders to see whether either misses fire, is to cut out all of the spark plugs except one, and then test that, and so with all the others in succession, and in this way the location of the trouble will be discovered.

Spark Plugs.—It is also the case that carbon deposits on the plug points will become heated up to such a point that pre-ignition will take place. Over-heated cylinders may cause this, and in certain cases, where the rotor arm wears, at the contact point, it leaves a trail of metallic particles over which the current will travel.

The Weather.—Cold weather is often a serious check to the starting of an engine, the water jacket, or some of the piping may be frozen, or the lubricating oil may become too thick to render proper service.

Drainage.—A careful operator will see to it that when the car is left all the water will be drained from the pipes and the water jacket and pump, and the parts can be dried out by running the engine for a minute or so, during the time of draining, so as to heat up the parts.

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