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Horseless Carriage Education

Technical Articles

Seals ( not the kind that swim)

 
Author: Harold Sharon


     Keep the oil in.  Keep the dirt out.  It sounds so simple. Why is seal design still evolving?       Didn't the seals on our brass cars seal?        Felt and leather were the common seals on these cars.        They sealed pretty well.

        Dense felt (matted wool) held back high viscosity oil and grease.

        Nicely feather-edged leather seals worked admirably on lighter oils.

          For water pumps flax fibers (linen) soaked in water-resistant oil worked fairly well.

        So why aren't we using these today?           These natural materials are variable; quality control is difficult.          Today's engines run faster, hotter, and with greater pressure differential across the seals, and....we won't put up with "pretty good" anymore. We also expect a lot longer life of our seals.

        On modern cars the old materials are universally replaced by synthetic rubber, polymers, and plastics. These new materials work well too .. well in one way. A leak-proof rubber seal will keep the shaft that it's running against dry, and it will wear out fast.   Or, oil reaches one side of a wheel bearing seal and the seal keeps the rubbing interface free of lubrication.

          The natural materials used in the old days were leaky enough to provide a wet interface.  Now seal manufacturers try to get "wet-faced" seals by incorporating very fine "scratches" into the face geometry, allowing slight "leakage" .   Valve stem seals have elaborate micro-leaks to allow oil to weep down the stem. This cools and lubricates the seal and the stem.

        Achieving a small leak like this is truly high tech.

     Head gaskets are seals, too. They suffer when the clamping force changes, as it does when a cylinder head heats and cools. If you have an aluminum head on a cast iron block, on your new or antique car, then you have a gasket trying to seal while the part on one side of it is expanding more than the part on the other.  It is a problem not yet solved; the wizards are still working on it.

For more of Harold's Great technical knowledge, check out His Book

 

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