Fig. 13—Three positions of a Valve Cam.
[Fig. 13] shows three positions of one of these revolving pieces of steel, technically called cams, first, in the act of just starting to raise the valve; second, its position when the valve is entirely open; third, its position when the valve has just closed. If both valves are operated by these cams you can see that if they are set at the proper position they can be opened at different times and entirely independent of each other. If you will look at [Fig. 3] you will see a complete motor, the inlet valve on the left side, and the exhaust valve on the right side. This figure will also show you the little cams in their various positions at different points of the four strokes. Sometimes the two valves, instead of being on opposite sides of the cylinder, are placed on the same side, and both cams are put on the same shaft, which, by the way, is called a cam-shaft.
Fig. 14—Names of Valve Parts.
[Fig. 14] shows two such valves, the left hand one opening, and the right hand one closed. The extreme left hand view shows the way they would look if viewed from the end. It also gives you the names of all the parts.
[Fig. 7] shows how the valves are “ground in.” The way you do it is to take the valve out, and coat it with very fine emery dust and oil, and then put it back in place leaving off the spring, fit a wrench to it on top as shown in the picture and twirl it around as you would a glass stopper in a bottle until it is perfectly air-tight, after which the valve should be removed and both it and the valve seat carefully wiped off so that none of the emery will get into the cylinder or other working parts of the engine and cause them to be cut.
There are several different ways of making valves and several places to put them so that you must not always expect to find them in the same place. Their action is the same, however, no matter where they are situated or how they are operated, and I think with a little examination and study you will always be able to find them and understand how they work in any engine.
THE PISTON
The piston forms, as you will recall, the bullet in the cannon, which instead of leaving the barrel, was made to travel back and forth inside of the cylinder under the action of the explosive gas. Owing to the fact that a solid piece of iron would be very heavy and would get very warm, the real piston used in a motor is made hollow so that it is merely a shell. Instead of fastening the rod to the end of it, a small rod, called the piston pin is in the center of it, and to this the connecting rod is connected. [Fig. 16] shows a section of the piston. You will notice that the piston pin is kept from sliding sideways by a bolt that is screwed into it.
