The pistons are one of the most important parts of an engine, because they are the mechanisms that contains the engines energy. The pistons are located in the cylinder block. The number of cylinders in an engine can vary.

Inside the cylinder a mixture of fuel and air is injected through the intake valve. Pressure in the cylinder is created when the piston returns to the top of the cylinder from its previous cycle. When the pressure is greatest the spark plug, located at the top of the cylinder, ignites the gas and causes an explosion. The piston is the sent downward extremely fast. The energy travels through the Connecting Rod, which is connected to the bottom of the piston, and the linear motion is converted to rotational motion through the crankshaft. The crankshaft is connected to the transmission, so when the crankshaft turns, the wheels turn also.