Two Wheeler Engines: Engine is a unit of motorcycle that runs the motorcycle by converting fuel energy to mechanical power. This power comes from the burning of fuel inside the cylinder of the engine.

The engine of a motorcycle can be classified as follows :

(a) According to Engine Strokes

(i) Two-stroke Engine : One power stroke in one revolution of engine crankshaft.

(ii) Four-stroke Engine : One power stroke in two revolution of engine crankshaft.

(b) According to Cooling of engine :

(i) Liquid Cooled Engine

(ii) Air Cooled Engine : These can be of two types as given below :

• Natural Air Cooled Engine
• Forced Air Cooled Engine

Here, we shall study four-stroke petrol engine only because this is used in Hero Honda motorcycles. The petrol engines are also known as spark ignition (SI) engines.