Intake Stroke

• The first stroke is the intake stroke in which the intake valve opens and air and fuel enter the cylinder as the piston moves out of the cylinder.
  
  

Compression Stroke

• The inlet closes as the piston re-enters the cylinder. The air and fuel have nowhere to go yet, so they become compressed in the chamber. When the piston reaches the end of this stroke, a spark is fired into the chamber, igniting the air and fuel mixture.
  
  

Combustion Stroke

• The ignition of the fuel and air forcefully pushes the piston back out of the cylinder. This forceful motion is what creates power in the engine.
  
  

Exhaust Stroke

• The recoiling effect of the combustion stroke causes the piston to re-enter the chamber. When it does an exhaust valve is opened, and the entering piston pushes out the gases that remain from the combustion. When this stroke is completed the intake opens, the piston is drawn out of the cylinder and the process repeats.