The cylinder is bolted to a framework called the crank case which furnishes a solid foundation upon which it can rest.
VALVES
You will remember that in first discussing the drawing in and cleaning out of the gas that two holes had to be cut in the sides of the cylinder wall. One of these through which the fresh gas might be sucked in, and the other through which the burnt gas might be expelled. Also remember that we kept these holes plugged except when it was necessary to have them open to perform their work.
Fig. 11—The evolution of a Valve.
Fig. 12—A regular Valve.
Now let us take a section of a valve and see how it is made up. You will notice first the little plug “A” which covers the hole in the cylinder; it is tapered very much like a glass stopper in a bottle for the reason that in this form it is easier to fit it to the opening; it can be “ground in” in the same way that a glass stopper can, in order to make an air-tight fit. “B” is a rod known as the valve stem, and is simply a round piece of steel fastened to the valve plug “A.” “S” is a valve spring which holds the valve down into the cylinder wall, or valve-seat, as it is called. In order to open these valves you can see that all that is necessary for you to do is to push up on the valve stem “B.” This will raise the valve “A” away from its seat into the position shown by the dotted lines, leaving a space all around through which the gas may enter or leave. In an actual motor, however, little irregular pieces of steel, cut out in general shape shown in Fig. 14 perform the operation of raising the valve.
