The Exhaust stroke.
The exhaust stroke is the final stroke of the four-stroke cycle engine. It occurs when the stroke valve is open and the intake valve is closed as can be seen in the picture above. The piston in this stage moves upwards from BDC to TDC. The exhaust valve opens other moving parts like the wheel which pushes the piston back to TDC. This action emits the spent air-fuel mixture through the exhaust valve.
