The four-stroke cycle gets its name from the four stages of the up and down motion of pistons within their cylinders. The strokes are intake, compression, combustion, and exhaust.

The first stroke of the four-stroke cycle is the intake which can be described in two parts. First, as the piston reaches the top of the cylinder the intake valve opens.  In the second part, the piston moves down to create a partial vacuum that draws a mixture of fuel and air into the cylinder via the intake valve.  

The next stroke of the cycle is compression. This is also a two-part action. The first stage occurs when the intake valve closes to seal the cylinder that is now full of the air/fuel mixture.  The second stage of compression is when the piston moves up within the cylinder causing the air-fuel mixture to be compressed.  

Next up in the cycle is where the fun begins, the combustion. This stroke is also made up of two actions. The first is the spark from the spark plug to ignite the compressed air-fuel mixture inside the cylinder. The second part of the combustion stroke happens when the air-fuel mixture within the cylinder explodes or combusts, forcing the piston to be pushed back downward within the cylinder.

The fourth step of the cycle is the exhaust. Just as in the other strokes, it can be broken into two actions. First, when the piston reaches the bottom of the cylinder after combustion, the exhaust valve opens. The second half of the exhaust stroke happens when the piston travels back upward in the cylinder and forces the burned gases through the exhaust valve. After this stroke occurs, the entire cycle starts over again.

Converting this energy to power the wheels on your car is achieved the following way:.

Each piston is attached to a metal pole called a connecting rod. This rod, in turn, is connected to the crankshaft. This linkage turns the up and down linear motion of the pistons into the circular rotational motion needed to drive the wheels of the car through the transmission.