Comp Cams offers a complete line of valve stem seals, from the stock GM ''O-Ring'' to the positive-stop Teflon seal. These seals are 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 sheild. The umbrella seal is normally used when a larger-than-stock diameter spring is used, in the case of a double spring, the positive-stop Teflon seal is used. There is also a smaller diameter Viton seal 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 guide with a special .530'' diameter cutter. Whenever you are planning an overhaul or a cam change, don't forget the valve seals - Comp Cams hasn't!