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Stripped Magnetic PlugThreads

in 912 / 914 Technical Questions 7 years ago
Hello,
What is the best way to repair stripped threads in the crankcase magnetic plug? The plug inserts normally until it contacts the seat, from there it will not tighten. If a Helicoil is needed, what size and thread?
Thanks
Ray Moran

  • Re: Stripped Magnetic PlugThreads

    by » 7 years ago

    The Magnetic plug is M12 x 1.5
    Unfortunately, if you had to ask, you probably are not up to the job.

    Any of the Threaded insert brands are going to require that you drill and tap the hole for the insert.
    Without splitting the case, it is going to be nearly impossible to prevent losing many of the Drill and Tapping Chips inside of the case.
    Drilling slowly with Heavy Grease, Q-Tips, and a ShopVac to catch all the chips might work if you get lucky.
    Some of the Inserts have a tab on the inside end that gets broken off after insertion.
    Keeping this out of the engine will be a problem.
    You really need to have access to the back side of the hole and that will require a Major teardown of the engine.

    The Magnetic plug is Not structural. It only needs to be tight enough to not leak and not fall out.
    You might be better off just using some Low Strength (Purple) Locktite and just snug it up to the point where it bottoms out.
    The Locktite will leak-seal the threads and hold it plenty tight enough that it will not back out.

    Next time do not get so aggressive with the wrench. 15 Nm is all that is needed.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

    Thank you said by: Raymond Moran
      
    Report

  • Re: Stripped Magnetic PlugThreads

    by » 7 years ago

    Take a look at the following photo:
    http://contrails.free.fr/images/rotax/DSCN5167.sized.jpg

    Looking at the photo the aperture through which the magnet protrudes is smaller than that for the thread. That being the case you could probably 'seal' this hole whilst you are working on the thread. That said, you will have to tap a shallow blind hole and it may be tricky to drill and tap it square-on.

    Worst case is that you will have to remove the gearbox, which is relatively straightforward. That being the case it should be possible to protect the internal components and collect up the swarf from any repair work.

    At this point, Bill's suggestion is looking mighty appealing!
    Thank you said by: Raymond Moran
      
    Report

  • Re: Stripped Magnetic PlugThreads

    by » 7 years ago

    I removed the gearbox and it was not that bad.
    Again Thanks
      
    Report

  • Re: Stripped Magnetic PlugThreads

    by » 7 years ago

    Glad it worked out.

    Watch your torque. This one does not use the typical Wall Chart numbers.
    While even a lowly Grade 5, 12mm Steel Bolt can take 40-70nM (~30-50ft-lb) depending on whose chart you look at...
    This is an Aluminum Bolt into an Aluminum Block and not a lot of treads at that!
    The Manual only calls for 15nM (~11ft-lb).
    About one-third of what you would use for the lowest numbers for Steel.

    You will easily strip this one out if you use the numbers for steel.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

    Thank you said by: Raymond Moran
      
    Report
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