The engine cycle

The     diagram        show       in       more   detail     the  piston / cylinder / crankshaft set -up. The inlet  valve opens to allow fuel mixture (gasoline and air) into the cylinder. A spark from the spark plug sets the mixture burning. The outlet valve opens to let the burned gases escape. The pis- ton rings from a tight seal between the piston and cylinder walls. The connecting rod joins the piston to a crank on the crankshaft.