There are certain events that must happen in a gasoline motor before the engine will run of its own accord. For instance, to obtain successive power impulses, the charge must first be admitted to the cylinder and compressed; it must then be ignited to form the explosion that creates the force at the flywheel; and the burned gases resulting from this explosion must be ejected in order to clear the cylinder for the new charge. To accomplish this series of events, some motors require four strokes, while others do the business in two. These are popularly called four-cycle and two-cycle motors, respectively. A cycle, of course, can be any round of events, such as a cycle of yearsmdash;at the end of which time the previous happenings are scheduled to repeat themselves. But in gas engine parlance a cycle is taken to mean the round of events from, say, the explosion of one charge to the ignition of the next. Thus, it will be seen that the four-cycle motor requires four strokes of the piston to accomplish its round of events, and is, properly, a four-stroke cycle motor. Likewise, the so-called two-cycle motor requires two strokes to complete its cycle and should therefore be termed a two-stroke cycle motor.
