5 minute 4 stroke lesson, or how your engine works.

This quick lesson will apply to most engines in most bike, why do I say most? 2 strokes work differently and I will cover those shortly.

There are 4 phases that your motorcycle engine go’s through to make power they are.

1. Intake:  The intake valve is open the piston is moving downward towards BDC (Bottom dead center or the lowest point in the stroke) and creating a low pressure area above the piston this draws fresh air and fuel into the combustion chamber past the intake valve or valves (their can be more than 1).

2. Compression: The intake valve or valves close and the piston begins its move upward toward TDC (top dead center where the piston is at its highest point in the stroke) the piston squeezes the air and fuel into a small pocket near the spark plug (this is where your compression ratio comes into play and we will cover this later).

3. Power: The piston is at TDC and the spark plug is fired (this actually happens just before the piston reaches TDC) the spark from the plug ignites the air fuel mixture which expands and pushes down on the top of the piston which moves the piston back towards BDC. Gasoline if watched in a slow motion movie does not explode, it burns across the top of the piston with a flame front that is predictable (for the most part).

4. Exhaust: The piston reaches BDC and heads back to TDC, the exhaust valve opens and the movement of the piston upwards forces the spent air and fuel mixture out of the cylinder and down the exhaust. The exhaust system itself can if designed correctly help the cylinder scavenge the burned air and fuel and remove it from the cylinder head faster and with more efficiency.

Intake, compression, power, exhaust….all engines have these 4 phases some are moved or altered slightly but they are basic to the function of an internal combustion engine.