Valve Stem Seals

Valve stem seal (VSS) is installed in the valve guide in the engine head. And it is preventing that engine oil supplied in a head flows into a combustion chamber by going through a valve stem and the sliding surface of the guide.
However, unlike a general reciprocating oil seal, since the sliding portion requiring lubrication is located on the outside of the seal (on the side where there is no oil), by making a small amount of oil leakage, the lubricating oil can be supplied to the sliding portion It has the ability to replenish.