What is a Valve Stem Seal?
Valve stem seals allow a controlled amount of oil to lubricate the valve stem as it moves in the valve guide. The amount of oil that passes by the valve stem seal must be precisely controlled. Too little oil causes stem and guide to wear; too much oil causes carbon build-up on valves resulting in a decrease in volumetric efficiency and rough idle, carbon build-up on piston tops resulting in detonation/pre-ignition issues, increased emissions, catalytic converter degradation, and excessive oil consumption.