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Thread: Missing rocker shaft thrust buttons

  1. #1

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    Default Missing rocker shaft thrust buttons

    Removed valve covers from a PA-22's O-320 yesterday to replace gaskets, and found that thrust buttons had never been installed in the rocker shafts. Are they required? I recently built a bigger experimental Lycoming and installed the thrust buttons.

    There were definitely some grooves on the inside of the valve cover on this 320. Is it acceptable for the shaft to contact the cover? Or is a poly thrust button required?

  2. #2
    Steve Pierce's Avatar
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    Default Re: Missing rocker shaft thrust buttons

    I sure wouldn't want to fly engine without them. I would think it would eventually wear through the rocker cover.

  3. #3

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    Default Re: Missing rocker shaft thrust buttons

    Depends on the age of the Lycoming.... some of the old ones never had them and the rocker shafts were longer. They did eventually wear on the valve cover. That's why the factory went to the plastic plugs and a shorter rocker shaft.
    Tom Ferraro
    PA22/20-160 N25TJ

  4. #4

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    Default Re: Missing rocker shaft thrust buttons

    Quote Originally Posted by tferraro View Post
    Depends on the age of the Lycoming.... some of the old ones never had them and the rocker shafts were longer. They did eventually wear on the valve cover. That's why the factory went to the plastic plugs and a shorter rocker shaft.
    Yep I had a 1968 Cardinal in 1979 with 1100 hours that the shaft wore a hole in the valve cover. The engine had never been messed with.

  5. #5
    Jim Hann's Avatar
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    Default Re: Missing rocker shaft thrust buttons

    Quote Originally Posted by BPL View Post
    Removed valve covers from a PA-22's O-320 yesterday to replace gaskets, and found that thrust buttons had never been installed in the rocker shafts. Are they required? I recently built a bigger experimental Lycoming and installed the thrust buttons.

    There were definitely some grooves on the inside of the valve cover on this 320. Is it acceptable for the shaft to contact the cover? Or is a poly thrust button required?
    Went throughout the tear down and build up classes by Lycoming at Oshkosh. Yes, you need them. Both instructors made a big deal about removing and replacing them during the classes. Apparently they find many engines with them missing.


    Sent from my iPad using ShortWingPipers.Org mobile app
    1957 PA-22/20 "Super Pacer" based 1H0
    Lifetime EAA member
    Vintage Aircraft Association member
    Lifetime EAA Chapter 32 member


  6. #6

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    Default Re: Missing rocker shaft thrust buttons

    Guess the point is that the Teflon buttons require a shorter rocker shaft, you cannot use them with the longer shafts. Also, if you don't mind using aftermarket rocker covers, Aircraft Specialties in Tulsa have them for around $20 each. I see on ebay guys are asking way over that for used ones.....that say Lycoming....Seems like a no brainer to replace rusted or worn rocker covers at that price. (SL61247 $20.95) they look cad plated. I put them on without paint and have not had any corrosion problems.

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