Motor cycle principles and the light car

The small space available on a motor cycle, and the necessity for keeping the weight low, has forced the production of devices quite different from the corresponding parts of an automobile, and the purpose of this book is to make dear their principles and operation.

Distinctive parts of the cycle car, as well as those mechanisms of the Ford car that differ from standard automobile practice, are also described, and text and drawings have been produced with the object of making the subject easily understandable.

The chapters on the care of the machine and on the causes of trouble should make it possible for the novice to handle his mount or car with efficiency and some degree of skill.

As the sole aim has been an explanation of principles, no attempt has been made to go into the details of construction of the different machines. It is believed that when a principle is understood, its application as embodied in a specific mechanism will be readily comprehended.

If one is asked the question, “What makes a motor cycle god” the natural answer is “The engine” and if the questioner is anxious for more information he will examine an engine to see what it is like and how it works. He finds that it has a shaft that may revolve, and that this is so connected with the driving wheel that when it turns it makes the wheel turn. Then he goes further to see what makes the shaft turn, and finds the shaft provided with a crank to which is connected a rod, the upper end of which is attached to a plunger that slides in a cylinder.

The arrangement is exactly like a pump. He recalls that in a pump the shaft must be driven in order to make the plunger slide in the cylinder, however; he sees that while the engine may look like a pump it is in reality exactly the opposite, for the pump requires power to drive it while the engine is a power producer. He realizes that something must happen inside of the cylinder to make the plunger or piston turn the crank shaft, and asks for information. It is quite evident that pressure must be applied to the piston, but how is that pressure produced?

In the answer to this is the true answer to his first question. It is heat that produces pressure against the piston, and thus it is heat that makes the engine go and that drives the motor cycle and the automobile.

When anything is heated, it becomes larger, the most familiar example of this being the mercury in a thermometer. On a cold day, the mercury occupies only a small space, filling the bulb and a little of the tube. As the temperature goes up, the mercury becomes larger in volume, and in expanding to occupy more space it rises in the tube. When air is heated, it also expands, and as is the case with any gas, its expansion is far greater than the expansion of metal or of any other material.

Going back to our engine, let us suppose the cylinder to be filled with cold air , and imagine that air to become heated. It immediately endeavors to expand, but in order to do so it must make more room for itself. Its only way to do this is to displace the piston a sufficient amount to give the additional space required ; it follows that in moving the piston the crank shaft must turn. At first glance it would hardly seem possible for heat to make a crank shaft turn, but the matter becomes clear when we see that the heat makes the air expand, and that the air thus becomes the go-between, so to speak.

Having determined the principle tinder which the engine operates, we may get down to the practical side of it and learn how the principle is applied. The usual way to heat a thing is to build a fire under it, but this could hardly be done in the case of an engine. Another way is to set fire to the thing itself. Here we meet the objection that air will not bum, but we can get around this by mixing the air with a gas that can be burned, and setting fire to the mixture. By its own burning the mixture becomes intensely heated, the air expands, and the engine runs.

There are a number of gases that might be used to make a combustible mixture; illuminating gas, for instance, or acetylene gas, but these would, not be convenient because of the difficulty of carrying a sufficient supply on a motor cycle or automobile. It is far simpler to use gasoline, for this may be carried as a liquid and turned into gas only when gas is required.

To make our engine run we must form a mixture of gasoline gas and air, put it into the cylinder, and set fire to it. When it has burned, and has done its work in making the crank shaft turn, the used-up gases must be cleared out of the cylinder to make room for a new charge. In this the engine is much like a muzzle-loading gun, which must have the powder, wadding and bullet put into the barrel and rammed down before the gun can be fired; after firing the barrel must be cleaned out in preparation for the next charge.

The firing of the gun drives the bullet the length of the barrel, just as the burning of the charge in the engine moves the piston the length of the cylinder. In the gun a new bullet is used for each shot, while the piston, having been moved to the outer end of the cylinder, is moved back again by the crank shaft to receive the next charge.

In order that the engine may run, this series of things must take place in regular order; for if there is any interference, the action will stop. The charge of mixture must be taken in and rammed down, so to speak, in order to make it bum quickly and properly; then it must be set on fire, and finally the burned and useless gases must be cleared out of the cylinder to make room for a fresh charge.

This series of events is called the gas-engine cycle, the word cycle meaning a number of happenings, each one depending on the others and taking place in regular rotation. No matter how many cylinders an engine may have, each cylinder may be taken as a separate and independent engine, the cycle being performed in each one regardless of the others, and each one producing its proportion of the power.

We are already familiar with the principal parts of an engine; that is, the crank shaft, the piston, the connecting rod that connects the two, and the cylinder in which the piston moves. When the gas mixture is burning, the piston moves from the inner end of the cylinder toward the outer end, and then produces power and makes the crank shaft turn. Having reached the outer end of the cylinder, or, as it is called, the end of the stroke, it ceases to deliver power; some means must then be found to move it back to the inner end of the cylinder. This is done by a fly wheel that is attached to the crankshaft. When a wheel is started turning it tends to continue to turn; thus the fly wheel, having been started turning by the movement of the piston, will keep on turning, taking the crankshaft with it. The piston, being connected to the crank shaft by the connecting rod, will thus be moved, and will slide back and forth in the cylinder until the fly wheel stops turning.

This back and forth movement of the piston is depended on to clear the burned and useless gases out of the cylinder, to draw in a fresh charge, and to prepare the charge for burning. Each of these three acts takes place during a single stroke of the piston, a stroke being the movement of the piston from one end of the cylinder to the other; on an inward stroke the piston moves away from the crankshaft, while on an outward stroke the piston moves toward the crankshaft.

In going through the cycle the piston makes four strokes, and the crank shaft makes two revolutions. During one of these four strokes the engine is developing power and the piston is driving the crank shaft; during the remaining strokes, which are called the dead strokes, the crankshaft is moving the piston.

Our engine thus develops power for only one-quarter of the time that it runs. In running for an hour, for instance, it actually develops power for only fifteen minutes; during the remaining forty-five minutes it is performing the dead strokes, and the piston is kept in motion by the spin of the fly wheel.

There must be exact control over the ad- mission of mixture to the cylinder, as well as over the exit of the burned gas, and this is obtained by valves, of which each cylinder has two. One valve admits fresh mixture and is called the inlet valve; the other permits the burned and useless gas to escape and is called the exhaust valve. The valves are opened by the engine, and are closed through the action of springs. In order to handle and operate an engine with any kind of skill, the cycle should be well understood, and we will therefore take it up stroke by stroke.


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Motor cycle principles and the light car