How many revolutions must the crankshaft make when a four-stroke engine completes a working cycle?

In a four-stroke engine, the combustion cycle consists of four distinct strokes: intake, compression, power, and exhaust. Each of these strokes requires a specific movement of the piston in the cylinder.

As the piston moves down during the intake stroke, it draws in the air-fuel mixture. The piston then moves back up during the compression stroke, compressing the mixture. Following this, the spark plug ignites the compressed mixture, forcing the piston down during the power stroke. Finally, the piston moves back up again during the exhaust stroke to expel the combustion gases.

For each complete cycle of these four strokes, the crankshaft must rotate twice to accommodate the piston’s movement through its full range — down for two of the strokes and up for the other two. Therefore, to complete one working cycle of a four-stroke engine, the crankshaft makes two complete turns. This is why the number of revolutions needed for a four-stroke engine to complete its working cycle is two turns.