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piston ring operation and cylinder lubrication 4 stroke piston piston rings cylinder wall wrist pin connecting rod crank pin crankshaft piston first top compression ring second compression ring oil control ring ring lands cylinder wall oil relief holes as the crankshaft rotates oil is pumped to the crankpin bearing as the oil gets pumped through and out of the crankpin bearing it gets flung against the cylinder walls because of the rotation of the crankshaft as the piston moves downward in the cylinder the oil control ring scrapes the cylinder wall clean of oil routing the excess oil through the oil relief holes drilled in the piston since everything is moving so fast the oil actually gets sprayed through the oil relief holes and lubricates the wrist pin bearing piston to cylinder clearance exaggerated for illustration purposes combustion pressure piston ring lands top compression ring second compression ring cylinder wall the function of the top ring is to seal the combustion chamber during combustion the pressure of combustion actually exerts force on top of and behind the ring helping seal the combustion chamber during combustion the function of the second compression ring is to aid the top ring in sealing against combustion gases and to aid the lower oil control ring in scraping the oil off the cylinder walls so oil doesn't get in the combustion chamber