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positive valve stem seals

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  • Engine: positive valve stem seals

    (this may be a second posting)

    The bronze valve guides on my 289 were machined for Positive Valve Stem Seals, which I installed. The engine has been passing increasing amounts of oil smoke since (w/ about 1,000 mi. since rebuild).

    Several engine builders advised that positive seals should NOT be used on a "street" type engine, that the "normal" amount of oil supplied to the valve train is insufficient, that positive seals were meant to control massive amounts of oil supply. All the seal suppliers (Summit, Jegs, Speedway, CompCams, plus a couple others) state the seals are fine for a "street" built engine - That the seals are designer to allow the necessary amount of lube to be supplied to the stem and guide.

    I am now faced w/ the choices of replacing the positive seals OR pulling the heads and replacing the machined guides with stock guides and umbrella type seals.

    Anyone have experience w/ positive stem seals?

    Any opinions are welcome and appreciated.

    PaulTK

  • #2
    Originally posted by Paul Keller View Post

    Several engine builders advised that positive seals should NOT be used on a "street" type engine...
    Not for street? Better tell all the cars manufactured since 1979 they have the wrong seals on the valves.

    I've had the positive seals added to all my Stude engine rebuild and have had no issues after 10's of 1,000s of miles.

    When you say excessive oil consumption and smoke, is this all the time, or just when you accelerate?

    If it is all the time, maybe the rings did not seat properly or the oil rings were not installed properly..

    Click image for larger version

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    • #3
      Originally posted by Paul Keller View Post
      (this may be a second posting)

      The bronze valve guides on my 289 were machined for Positive Valve Stem Seals, which I installed. The engine has been passing increasing amounts of oil smoke since (w/ about 1,000 mi. since rebuild).

      Several engine builders advised that positive seals should NOT be used on a "street" type engine, that the "normal" amount of oil supplied to the valve train is insufficient, that positive seals were meant to control massive amounts of oil supply. All the seal suppliers (Summit, Jegs, Speedway, CompCams, plus a couple others) state the seals are fine for a "street" built engine - That the seals are designer to allow the necessary amount of lube to be supplied to the stem and guide.

      I am now faced w/ the choices of replacing the positive seals OR pulling the heads and replacing the machined guides with stock guides and umbrella type seals.

      Anyone have experience w/ positive stem seals?

      Any opinions are welcome and appreciated.

      PaulTK
      Several decades ago I was advised, by an engine builder whom I held in high regard, of those same problems with the positive seals, as well as eventually excess wear of the valve stem surface. I heeded his advice and have never used them, instead use OEM umbrella seals. I have never had a problem, and usually get around 100,000 miles between rebuilds; usually around 5000 miles per quart of oil on a fresh rebuild, for the first 25,000 miles or so, then it begins to drop gradually, to around 1000-2000 MPQ for the remaining life of the rebuild.

      I believe you can install OEM seals without removing the heads or changing valve guides. They seldom stay down snugly on the guide tops anyway, and often float up against the bottom of the valve spring collars, but still does not affect oil consumption.
      Last edited by JoeHall; 06-26-2019, 03:18 PM.

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      • #4
        My machine shop quit using positive seals. Said it was too hard on the guides. So I use stock guides and umbrella seals. Have had no complaints. I just took a set of heads apart that had positive seals. The valves had a build up of oily carbon on them.

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        • #5
          I normally run a PC type seal on the intake and an umbrella or no seal on the exhaust.
          I just took apart an "offshore" cylinder head...it had a very expensive, fancy...PC type seal on both the intake and exhaust.

          Mike

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          • #6
            You state bronze guides. Where true bronze guides used or the thin wall liners where the guide is drilled and a very thin bronze liner drove in? I have never seen a used set of head I don't care what the mileage is with the liners where they where not wore out. Now that tells you something. Use either new cast iron guides or the full bronze guides. Use of just an umbrella seal on the intakes if iron and nothing on the exhaust. I never like to use a seal other the the o ring type on bronze because they need some oil so they don't stick or wear the valve stem.

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            • #7
              The machinist that did the heads on my 259 recommended and used the seals as Mike normally runs. Umbrella on the exhaust and positive seal on the intakes.

              Charlie D.

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              • #8
                "I normally run a PC type seal on the intake and an umbrella or no seal on the exhaust."

                X2. Think about it. There is no vacuum on the exhaust guide when the valve is open. Just the opposite of the intake.

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                • #9
                  Is it not possible that the rushing of the exhaust gasses past the valve guide could create a venturi effect?

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                  • #10
                    Thank you all for your experiences and responses - Very helpful.

                    Response to one question ( by S.Scopelli) - The smoke appears at the initial start of the engine, after a shut down of an hour or so duration - Otherwise the exhaust is clear.

                    Another question re: using Umbrella Seals w/ the bronze, flat top guides - Some contend that the umbrella seals could get hit the top of the guide, be damaged (by hitting against the guide) and spread pieces of the seal into the engine - Anyone have experience w/ umbrellas w/ flat top guides?

                    Many thanks again,
                    PaulTK

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                    • #11
                      Flat Top Guides? I don't know WHY anyone would use the WRONG Valve Guides when the correct shape iron ones are available.

                      If it worked for Studebaker for MILLIONS of Miles, I would not re-invent the Wheel.
                      StudeRich
                      Second Generation Stude Driver,
                      Proud '54 Starliner Owner

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                      • #12
                        The bronze guides (noted above) were machined for positive seals - which provides a flat surface at the top as part of fitment for the seals - All quite normal for positive valve stem seals.

                        PaulTK

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                        • #13
                          Originally posted by Paul Keller View Post
                          Thank you all for your experiences and responses - Very helpful.

                          Response to one question ( by S.Scopelli) - The smoke appears at the initial start of the engine, after a shut down of an hour or so duration - Otherwise the exhaust is clear.

                          Another question re: using Umbrella Seals w/ the bronze, flat top guides - Some contend that the umbrella seals could get hit the top of the guide, be damaged (by hitting against the guide) and spread pieces of the seal into the engine - Anyone have experience w/ umbrellas w/ flat top guides?

                          Many thanks again,
                          PaulTK
                          Normally, blue smoke will occur on med to hard acceleration if there are valve issues..

                          Constant smoke is rings..

                          But if only a puff of smoke on startup and then clears up right away, it may not be a big concern.. Think of it as upper cylinder lubrication..

                          As StudeRich noted, I use the guides made for Stude and have the machinist modify the top to accept the seal. He had a special cutting tool made to do just that and can cut any guide to accept the seal of your choice.

                          The pic I posted, I had them cut the height down a bit because I've up'd the lift on the cam..

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                          • #14
                            That tool is available though Goodson Inc. They sell machine shop tools. It doesn't cost that much and it fits into a standard 3/8 drill. easy to use.

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