COMP Cams offers a complete line of valve stem seals, from the umbrella seals to the positive-stop seal. These seals are a must to keep unwanted oil from entering the combustion chamber through the clearance in the valve guides. 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 seal is used. The umbrella seals require no machining, but with the 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.