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Bearing noise?

in 912 / 914 Technical Questions 9 years ago
My 912S has 730 hours time accumulated over 15 years in an experimental aircraft I built. Recently a "whine" has developed which I cannot identify the source. Sprag clutch replaced, gearbox rebuilt, carbs overhaul about 3 years and 150-180 hours ago.
Is it recommended the 912S be overhauled after 10 years?
Is it worthwhile to overhaul an engine 15 years old?
Anyone have suggestions of how to troubleshoot?
Thanks,
Dan

  • Re: Bearing noise?

    by » 9 years ago

    More likely pitting on the gearset. Look very closely at the small gear tooth flanks. If it is pitted then do not delay the gearset replacement; even small spallation can emit very destructive harmonics that will damage carbs, exhaust, wiring and the fuel pump. That will cost you a lot more than a new gearset.
    A good test is to try and balance the prop; if you have pitting the balancer will keep moving the weights and never give you a good IPS. If you can run a spectrum analysis you will see the nasty harmonics.
    Thank you said by: Daniel Ward
      
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  • Re: Bearing noise?

    by » 9 years ago

    Rob, is it possible to send pictures of the exact place in the gear box , where you could find pitting ?
    Thanks
      
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  • Re: Bearing noise?

    by » 9 years ago

    see pdf
    gearpitting.pdf (You do not have access to download this file.)
      
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