Theoretical Timing Diagram of a Four Stroke Cycle Petrol Engine:

Theoretical Valve Timing Diagram:

The theoretical timing diagram of a four stroke cycle engine is shown in the figure. Here, you can see that at the initial stage of the suction stroke, the valve opens and takes place between A to B. To complete this, the crankshaft revolves 180^o and the piston moves from TDC to BDC. At BDC the inlet valve closes and the compression takes place between B to C. The crankshaft revolves 180^o, and the piston of your engine moves from BDC to TDC.

At the C position, the fuel of your engine gets fired, and the expansion takes place in 180^o from TDC to BDC. Then, again the crankshaft revolves 180^o from BDC to TDC at C to D allowing the expansion of flue gases. Finally, from D to E the crankshaft revolves another 180^o, and moves from BDC to TDC to complete the exhaust stroke. This is how the engine valve timing of your engine is maintained, and the crankshaft revolves 360^o to complete the cycle. In a complete cycle, the crankshaft gets two rotations of 360^o.