COMP Cams® offers a complete line of valve stem seals, from the stock GM "O-Ring" to the positive-stop PTFE 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 shield. 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 PTFE seal is used. We also have a smaller diameter Viton seal available for triple spring applications. Both the O-Ring and the umbrella seals require no machining, but with the PTFE seal it is necessary to disassemble the heads and machine the top of the guide with a special .530" diameter cutter. Whenever you are planning an engine overhaul or a cam change, don't forget the valve seals--COMP Cams® hasn't!