Piston Rings

Piston rings are metal rings located on the outside of the piston that provide a seal for the fuel and air mixture in an internal combustion engine. They also prevent oil from entering the combustion chamber from the crankcase. Most pistons contain three rings, two for sealing the combustion chamber (called compression rings), and one for keeping oil outside of the combustion chamber and returning excess oil to the crank case(called oil control rings). The rings are build with a gap that closes to allow for expansion due to engine heat.