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912 ULS Won't Pull Through

in 912 / 914 Technical Questions 9 years ago
I'm new to rotax and just installed a used engine on an airplane I'm building. I'm preparing to purge the oil system. I have the top plugs removed. I went to pull the prop through as you do in the purge and got to a point where the prop stopped. Probably less than 1 rotation. It feels like a soft stop but it won't go further forwards. I don't want to hang all of my weight on it. Anyone have an idea what the problem could be? I haven't yet purged so there isn't oil in the case.
Thanks!

  • Re: 912 ULS Won't Pull Through

    by » 9 years ago

    I would suggest you have a stuck valve. A valve, or valves, being stuck in in the open position, probably due to the engine standing unused for a while. The stuck open valve is now hitting the piston hence why the engine won't fully turn over.
    Remove all the rocker covers and check valve clearances to confirm. If you find one valve with excessive clearance that is the problem one. You will probably need to remove the head on the offending cylinder(s) to sort the problem.
      
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  • Re: 912 ULS Won't Pull Through

    by » 9 years ago

    Thanks for the reply Alan. I did a little more investigating. I turned the prop backwards and it came free. Then forwards worked too. I was able to rotate it a few times forwards then is stopped again. I removed the valve cover to inspect. All of the rockers make constant contact with the valves.

    I turned backwards, it came free then forwards again and it spun freely. Several times around with no issues then it stopped again. Seems to be a repeated issue. What would the logical next step be?

    Wiggling the prop in the forward direction also seems to keep it moving but perhaps not as it should.
      
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  • Re: 912 ULS Won't Pull Through

    by » 9 years ago

    something has gone into one of the induction manifold and then into the cylinder? Or a big piece of carbon? Or oil?
    If you look at the squish zone in the cylinder you will see how even a tiny stone can stop the piston.
      
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  • Re: 912 ULS Won't Pull Through

    by » 9 years ago

    Update. Removed bottom plugs, blew air in top and caught what came out. Some carbon and a few pieces of hard whitish mineral looking stuff. Lead? I think that was the holdup. Now motor turns smooth as silk.
      
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