Functions of the Piston Ring

• To form a seal for high pressure gases from the combustion chamber, against leak into the crankcase.
• To provide sufficient lubricating oil on cylinder walls throughout the entire length of the piston travel, minimizing the ring and cylinder wear, and at the same time control the thickness of the oil film so that satisfactory oil film is maintained. The oil is not to be allowed to go up to the combustion chamber where eventually it would burn to leave carbon deposits on cylinder wall, cylinder head, piston or at the exhaust manifold and on valves seating (or piston pin).