MOTORCYCLE ENGINES must be lightweight and compact and have a good power output. They
have between one and six cylinders, can be cooled by air or water, and the capacity of the combustion chamber varies from 49cc (cubic centimeters) to 1500cc. Two types of internal combustion engine are common: the four-stroke, which is used in cars , and the two-stroke. A basic two-stroke engine has only three moving parts—the crankshaft, the connecting rod, and the piston—but the power output is high. The engine fires every two strokes (rather than every four), giving a “power stroke” every revolution. Power is conveyed from the engine to the rear wheel by the transmission system. This usually consists of a clutch, a gearbox, and a final drive system. Clutches are multiplate devices, which run in oil. Gearboxes have five or six speeds and are operated by foot pedal. Shaft and belt drive systems are used in some cases, but chain drive to the rear wheel is most common.
