Valve Stem Oil Seals, Metal Jacket Viton Seal 511-16 CO511-16 Suit 8mm Valve, .500" Guide .600" O.D, For LS1 & 26921-KIT VALVE STEM OIL SEALS, LS1 8mm 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.