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Thread: Stuck Exhaust Valves

  1. #41
    Eddie Foy's Avatar
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    The Gospel According to Mike Busch.

    "If the engine is operated with a rich mixture (particularly during taxi and other ground operations), lead, carbon, and other unburned combustion byproducts can build up on the portion of the exhaust valve stem that projects into the exhaust port when the exhaust valve is open. When the valve closes, this deposit build-up is dragged into the lower portion of the valve guide, and often causes accelerated guide wear (“bellmouthing”), particularly in Continental engines that use relatively soft valve guides. As we’ve seen, accelerated valve guide wear generally leads to valve hot spots (“burned valves”) and ultimately to valve failure (“swallowed valves”)."

    Quote Originally Posted by akwing View Post
    Can someone explain how leaning prevents a stuck valve?

    This problem has been solved years ago - run Marvel (or like-product) in the gas (and oil, if you want)...the old mechanics/aviators been using it for years to free/prevent sticky valves. I don't recall hearing them say to lean it more though.
    "Put out my hand and touched the face of God!"

  2. #42
    Eddie Foy's Avatar
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    The bulk of heat transfer in a exhaust valve occurs from the valve into the seat when it is closed.


    Quote Originally Posted by N86250 View Post
    I have wondered why aircraft valve guides don't get knurled. I see knurling as an old technology to extend valve guide usefulness. I suppose it might affect the heat transfer from the valve stem to the guide to the cylinder head and overheat the exhaust valves.
    "Put out my hand and touched the face of God!"

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