BC valve stem seals are designed for OEM Polaris (stock) top hat style seat. Integrated seat/seal for OEM valve guides when using stock or BC spring/retainer if running stock cams or cams under.430" lift. The seals allow a carefully defined amount of engine oil from the cylinder head into the combustion chamber—to lubricate the rotating valve stem in the valve guide. BC valve stem seals are produced from high performance materials for increased part life and lower wear.