A motorcycle engine is an engine that powers a motorcycle. Motorcycle engines are typically two-stroke or four-stroke internal combustion engines, but other engine types, such as Wankels and electric motors, have been used.
source/image(PrtSc): Engineering Animations
Although some mopeds, such as the VéloSoleX, had friction drive to the front tire, a motorcycle engine normally drives the rear wheel, power being sent to the driven wheel by belt, chain or shaft.
Single-cylinder engines have the cylinder vertical, inclined or horizontal, the last type most common in step-through motorcycles. Single-cylinder engines require both a larger flywheel and a heavier-duty gearbox than multicylinder engines. Small singles are cheap to build and maintain and are suitable as cheap utility motorcycles.
Most manual transmission two-wheelers use a sequential gearbox. Most motorcycles (except scooters) change gears (of which they increasingly have five or six) by a foot-shift lever. On a typical motorcycle, either first or second gear can be directly selected from neutral, but higher gears may only be accessed in order – it is not possible to shift from second gear to fourth gear without shifting through third gear.//wikipedia