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912ULS. Cyl #4 top right. Some years ago the cylinder head nuts were fitted incorrectly, with the sealed dome nuts on the top studs and the open nuts fitted inside the rocker cover. The engine leaks oil.  #4 top right dome nut is stuck to the stud.  There is approximately 3 to 4mm rotational movement but the threads (either end of the stud) are just not releasing. We cut the top off the dome nut to confirm that the stud moves with the nut. Penetrating oil has been tried and heating the nut had been tried. From the logbook, the nuts were torqued 3 years ago to 10Nm plus 180 degrees, not 120 degrees. Two nuts/studs were originally locked like this but I was able to free one of them. I believe the threaded insert inside the block is rotating.  Before sending the engine away to have the stud removed and have all 16 studs replaced.. I'm asking you chaps for a 2nd opinion or alternative suggestions.  The engine is in Caboolture. Thanks in advance. 

  • Re: Stuck Cylinder Stud

    by » 5 months ago


    Assuming that most everthing was done incorrectly...

    Assume they loctited the nuts on the top of the studs and that is why they will not release.

    You will need to get the nuts over 250°C to get them to release.

    Get a sheet of aluminum with a hole just larger than the nut in it to protect the head.

    Position the nut in the hole and heat the nut with an acetylene torch with a small flame.

    Propane will not be hot enough as the head will be a major heatsink.

    When the end of the nut just starts to glow dull red, very quickly get a socket on it and start cranking.

    You will have about 4 seconds so this will be a two man job.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


    Thank you said by: Stuart Erskine, RotaxOwner Admin

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