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The So-Called "Umbrella" Valve Stem Seals

Mar 9, 2009
On several occasions I have had the opportunity to see small block Viton "umbrella" seals after just 20,000 to 25,000 miles of use. Each time I found ALL of the seals were as hard as a rock and broken in half; the upper half still attached to the valve stem and the lower half (the skirt) had fallen down to the spring seat or lying in several pieces. I happen to have a used set of small block nylon umbrella seals that saw 100,000+ miles of use and they still look as good as new although they too are as hard as a rock. When it comes to valve seals the only seals that are worth using are the "positive" OEM seals that use a snap ring to secure them to the guide or the superior Perfect Circle Teflon seals that also use a snap ring to secure them but they also have a coiled wire "snap ring" that squeezes it against the valve stem.

I have two cutters for machining the guides for Teflon Perfect Circle seals; one for 11/32" valve stems and one for .371" valve stems. The cutters are pretty expensive at over $100 each but they are necessary for installing positive seals on big block valve guides because they aren't machined at the factory.

My advice? Never use any umbrella seals on a small block Chevrolet unless they are the nylon style that are almost impossible to find.


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    1971 Corvette Engine Rebuild October 2016 002 (2).jpg
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  • 1971 Corvette Teflon Valve Stem Seals 003.jpg
    1971 Corvette Teflon Valve Stem Seals 003.jpg
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