BMW Engine Piston Ring Set - Kolbenschmidt 11257594453

The purpose of piston rings varies based on their installed position but generally, they are responsible for combustion chamber sealing (compression), oil control, and heat transfer. The three types of piston rings are as follows:

Compression ring (top): The compression ring is the closest ring to combustion gases and is exposed to the greatest amount of chemical corrosion and the highest operating temperature. The compression ring transfers a majority of the heat from the piston to the cylinder wall/engine block.

Wiper ring/secondary compression ring (middle): The wiper ring, sometimes called the scraper ring, Napier ring, or backup compression ring, is the next ring away from the cylinder head on the piston. The wiper ring provides a consistent thickness of oil film to lubricate the running surface of the compression ring.

Oil control ring (bottom)- An oil ring includes two thin rails or running surfaces. Holes or slots cut into the radial center of the ring allow the flow of excess oil back to the oil reservoir. The oil control ring also has the most amount of surface pressure generally in order to control oil film.