This O-ring seals the interface between the cylinder head cover and the cylinder head on the engine of agricultural tractors and combine harvesters. It prevents oil leakage from the valve train area and keeps contaminants out of the engine's upper lubrication circuit. A hardened or cracked O-ring allows oil to weep past the cover, which can lead to low oil levels and potential engine damage if not addressed. This is an original part from the engine manufacturer, molded to the same cross-section and durometer as the original seal so it seats correctly in the cover groove without requiring additional sealant. On reinstallation, clean both sealing surfaces and torque the cover bolts in the sequence specified for the engine.