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the fuel/air/oil mixture from escaping out the ex- haust port. 

## Cylinder Compression Stroke—Piston Moving Up: Figure 4-3 e to f 

The piston then rises, and compresses the fuel mix- ture in the combustion chamber. During this piston compression process, the crankcase vacuum intake process is happening simultaneously, as described earlier. This is why four processes can happen in two strokes. 

## Cylinder Power Stroke—Piston Moving Down: Figur e 4-3 f to g 

At the top of the stroke, the spark plug ignites the fuel mixture and drives the piston down as the power stroke of the engine. 

## Cylinder Power Stroke—Piston Moving Down: Figur e 4-3 g to h 

As the piston passes the exhaust port, the exhaust starts to exit the combustion chamber. As the pis- ton continues down, the transfer port opens and the swirling motion of the air/fuel/oil mixture pushes the exhaust out the exhaust port. 

## Piston Reverses Direction From Down Stroke to Up Stroke: Figure 4-3 h to a 

As the piston reverses direction from the down stroke to the up stroke the process is complete. 

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