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I flew the plane for about an hour and had no problems - everything seemed fine. Upon returning I hand propped for checking the oil. There was a seriously concerning, loud scraping/grinding noise when turning the prop. It seemed to be coming more from the rear of the motor.

Suspecting that maybe it was related to the starter, I turned the motor over a couple of times with the starter - mags off - no problem detected. After this, I hand propped again and the noise was gone.

If the starter stayed engaged for the entire flight and warm-up, inculding 5 full throttle take-offs, I'm surprised it wasn't completely ruined.

Just and hour or so of tach time prior to this I changed the oil, inspected the mag plug, and cleaned the oil tank and there were no metal fragments anywhere.

 I guess my next step should be to remove the starter and look for problems? Any suggestions for me?

 

  • Re: 912ULS Noise Turning Prop

    by » 6 months ago


    Allen

    If the starter was engaged in flight the starter motor would have exploded.  No kidding.  The starter turns over 6000rpm at cranking to get the crankshaft to turn 250.  It can not be the issue.  If by chance you turned the prop backwards rather than forward you will hear the starter sprag drive the starter motor.  

    Cheers

     


  • Re: 912ULS Noise Turning Prop

    by » 6 months ago


    Thanks for the response. I did a couple of quick videos - one with the noise and one after it cleared up:

    https://youtu.be/umGA5jz0k_o?feature=shared

    https://youtube.com/shorts/61T2CoImtWY?feature=shared

    Any suggestions on how to diagnose this?

    BTW, this motor was built by Hal Stockman about 60 hours ago with a Zipper kit. And the clutch was refurbished during the build.

     


  • Re: 912ULS Noise Turning Prop

    by » 6 months ago


    Allen

    From the description you say it cleared up....I would then guess it was not fully pre-lubed internally.  it sounds a bit like dry gears and bearings.  if this cleared up by itself that would be the only reasonable explanation.  

    Cheers


  • Re: 912ULS Noise Turning Prop

    by » 6 months ago


    I always hand prop to "burp" the engine and check the oil before and after each flight. It hasn't made this noise before. Before flying, I hand propped and checked the oil as always. There was no noise. After flying this time when I hand propped it was making the noise. I turned it numerous times trying to determine where the noise was coming from. It seemed to come from the rear of the engine. Thinking it might be the starter, I cranked the motor over a couple of times with the starter with the mags off. There didn't seem to be any problem. After that, I turned the prop by hand again, and the noise was gone. As the plane was flown for an hour with normal oil pressure immediately prior to hearing the noise when hand propping and its never made this noise before, and the noise immediately cleared up after turning it over a couple of times with the starter, I don't find the suggestion that it had dry gears and bearings reasonable.


  • Re: 912ULS Noise Turning Prop

    by » 6 months ago


    I don’t know RW, that sounds more serious to me than dry gears and bearings. Did you watch the second video?  Could this be the starter sprag clutch coming apart and partially hanging up instead of slipping smoothly? The sound goes away after engaging the starter, and the sound is coming from the rear of the engine, both those things point me to the starter clutch. If the sprag cage or a sprag was broken it could cause this. Just speculation, but I would want to sort this out before flying it again. 


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