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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,

    The vibration was down to a very worn gearbox.

    The splines were worn on the prop shaft and slipper clutch, and the dogs worn on the drive gear.

    Over £2000 later it doesn't vibrate.

    Mark
      
    Report

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Funny you should say that, I have just got off the phone to a Rotax expert this afternoon and with all the information that I gave him he thought that the gearbox was a good place to look. I was warned that if the gears were worn then I would be in for a hefty bill. There would be the option to fit a slipper clutch for an additional £300 at the same time though.

    I don't think that I have any other option, so I will send the gearbox off to be inspected and report back the findings.

    Kevin
      
    Report

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Just a note and not aimed at anyone, just food for thought,

    Gearboxes should last, but they need to be inspected at their regular inspection intervals. Many gearboxes with the proper maint. and care can last to TBO without any issues other than shimming, but improper care or lack of care can cause a gearbox to need heavy maint. prematurely if let go for any time.
    Things that can cause premature wear which can cause unwanted vibrations are:
    wrong type of oil,
    Too heavy a prop and or prop inertia,
    failing to do your friction torque check at the 100 hr. and annual and failing to get the gearbox serviced when the test results are too low to meet specs,
    running the engine rpm too low on a regular basis,
    severely out of balance props.
    Special note: prop strike checks are important to find abnormalities that the eye can't see and must be performed. Just because it runs after a strike doesn't mean it isn't damaged.

    These may be some of the more common, but it isn't limited to just these.

    Gearbox issues rarely happen over night and it takes time to cause issues so just because it works okay today doesn't mean it will stay healthy later if proper care for the gearbox isn't performed and the proper maint. recommendations aren't followed.

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

      
    Report

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    To be fair, this gearbox has done 2500hrs. It has been stripped and re shimmed every 500 hrs.

    The friction torque has always been checked and maintained.

    The main wear was the splines which as they begin to wear, the speed they wear increases.

    The other damage was caused around 300 hrs ago when the plastic thrust washer broke which was picked up almost straight away but the gear faces were damaged, and after 2500hrs the dog faces were worn as well.

    I would definitely recommend changing the plastic washer at every gearbox service as it could fail at any time, and this will cause more expensive damage. I know they are not cheap, but it is cheaper than a new gear set.

    Mark
      
    Report

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Hi Mark,

    That's some good hours and lots of fun flight time on that engine and I bet it will keep on going.

    Good point on the plastic thrust washer.

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

      
    Report
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