Although the combustion engine seems a complicated piece of machinery, but it consists of the following basic parts: the cylinder, the piston, connecting rod, inlet and exhaust valves, the carburettor, sparking plugs and the crankshaft.

A piston moves in each cylinder of the engine, performing an up and down motion. The motion of the piston is transmitted to the crankshaft by way of the connecting rod and then on to the other parts of the mechanism that turn the wheels.

The movement of the piston goes through four stages or strokes. The first stroke occurs as the piston moves down the cylinder and the inlet valve opens and admits a mixture of air and petrol vapor from the carburettor. The piston then rises and strongly compresses this mixture until it becomes explosive. At this point an electrical spark jumps from the plug and causes the mixture to ignite. The resulting explosion pushes the piston down again causing it to turn the crankshaft which then turns the wheels. When the piston moves back up the cylinder, the cylinder's exhaust valve opens and the burnt gases are expelled. This whole process is repeated thousands of times per minute in four basic strokes: induction, compression, power and exhaust.