Valve Stem Oil Seals, O-Ring Type 501-16 CO501-16 Suit 11/32" Valve, .400" O.D VALVE STEM OIL SEALS, 11/32" Comp Cams offers a complete line of valve stem seals, a must to keep unwanted oil from entering the combustion chamber through the clearance in the valve guides. The O-ring seals use the standard retainer and oil splash shield. The umbrella seal is normally used when a larger than stock diameter spring is used, and in the case of a double spring, the positive top Teflon seal is used. Smaller diameter Viton seals are also available for triple spring applications. Both the O-ring and the umbrella seals require no machining , but with the Teflon seal it is necessary to disassemble the heads and machine the top of the guide with a special cutter.