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I have just replaced the sprag clutch in my 912ULS at about 700 hours. Several others in my area have had to replace theirs also. All of us have been running Mobil 1 synthetic motorcycle oil. The one who has had no problems with the sprag clutch has been running Aeroshel semi synthetic oil. It seems to me there may be a connection to sprag clutch problems and the full synthetic oil. If I understand the operation of the sprag clutch it relies on some level of friction to make the "dogs" move and lock in. Maybe the Mobil 1 is just too slick for the sprag. Has any one else seen a connection to it?? Or suspected it? I found no evidence of lead in the area. I run mostly no-ethanol unleaded mogas. When I am on a long trip and run avgas I alway run tcp.

Thanks --- Lynn
  • Re: Sprag Clutch and full synthetic oil

    by » 10 years ago


    I have used Mobile One Racing 4T full synthetic motorcycle oil over the years. I have many friends that have used it over the years too without any issues. The sprag clutch damage is usually caused by poor starting techniques, poor battery and poor carb setup. All or any of these may cause prop kickback. That is a sprag killer. Cranking and cranking the engine for long periods without a start may lend itself to damage over the long haul too.
    If any one of these guys had kickback you have your answer, but it isn't the oil.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: Sprag Clutch and full synthetic oil

    by » 10 years ago


    I agree with Roger.
    Be proactive if you are having any starting problems; it should start almost instantly, every time, and if it doesn't there are many remedies to cure the problem.

    Thank you said by: Lynn Coltharp

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