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912UL Engine vibration on throttle back

in 912 / 914 Technical Questions 12 years ago

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Hi Kevin

    If I was you I would stick with the standard gearbox. It is not as necessary in the 912 as compared to the 912s and it can cause the dreaded sprag clutch problems, and its cheaper :-)


    My gearbox has the sprag clutch fitted and it was badly worn, so that is not an issue. The only benefit you would get is that if you had a bad prop strike, the chances are you won't damage your crank.

    Mark
      
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  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Mark; How would an overload clutch cause sprag clutch problems? In my experience it makes starting better, not worse.
    Kevin, I recommend installing the overload clutch; then you have crankshaft protection when (not if ;) ) you have a propstrike. And you can measure and monitor friction torque so you know when your gearbox needs to be tightened up. It also rattles less at idle.
    Rob
      
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  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Hi Rob

    It is fairly well know that the slipper clutch causes the sprag clutch starting problems. I bet you don't get a sprag clutch problem in an engine without a slipper clutch.

    Also, if you don't fit the slipper clutch, you don't have to measure the slipper clutch friction torque.

    I will guarantee if you fit the slipper clutch, you will eventually get sprag starting problems. It is not necessary in a 80hp 912ul.

    An engine that is set up right won't rattle at idle.

    Mark
      
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  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    The sprag problem is pretty much 100% a 912S/ULS problem. Every 100hp comes standard with a overload clutch since 2003, in North & America, so what do you base your opinion on?
      
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  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    I'm with Rob on this one.

    Sprag clutch issues usually come from kick back, people rotating the prop backward, poor batteries and weak starters and not because the slipper clutch is in the gearbox. If having a slipper clutch in the gearbox caused this all the 912ULS engines in North America would be having issues since 2003. Like Rob said, without the slipper clutch you have no prop strike protection. I have 912ULS engines that I maintain with 1000-3000 hrs and haven't had a bad sprag.
    Kickback during starting if not corrected can be a sprag killer.

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

      
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