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Oil tank contaminated with big Carbon pieces

in 912 / 914 Technical Questions 8 years ago
Hello.

I'm doing a 1000 hour service on a 912ULS engine and found many and very big and small Carbon pieces (Coking pieces) in the bottom of the oil tank. :blink: See picture. See the screw placed besides the Carbon pieces for comparison, its a M4x16mm screw. Quite big pieces of Carbon.
I haven't seen so much Carbon in the tank before and are a bit concerned. Well in fact quite worried. :dry:

I haven't cut the Oil filter open yet, but will do it ASAP.

I haven't done service on this engine before so I don't quite know the service history of this engine but it should have been serviced according to LMM and have used Rotax AeroShell all the time.

Any comments and help to explain this, and perhaps suggestions what to do is highly appreciated.

Regards
MOL
20160721_220101s.jpg (You do not have access to download this file.)
20160721_225302s.jpg (You do not have access to download this file.)

  • Re: Oil tank contaminated with big Carbon pieces

    by » 8 years ago

    Brian,
    I suspect the debris is from a failed plastic thrust washer from the gearbox.
    Unlike carbon the plastic doesn't crumble when you squash it so it is easy to tell if it is carbon or plastic.
    Check the friction torque and see if it is lower than when measured on previous services, if it is then I would suggest you get the gearbox torn down & inspected.
      
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  • Re: Oil tank contaminated with big Carbon pieces

    by » 8 years ago

    Hi Brain,

    I'm with Conrad. (He's a good resource) He's definitely been around the block.
    This looks more like the phenolic thrust washer bits from the gearbox.

    If this is debris from that washer it should have stopped in the tank because of the screen, but I think I would pull my oil cooler and flush it out.

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

      
    Report

  • Re: Oil tank contaminated with big Carbon pieces

    by » 8 years ago

    Hello Conrad and Roger.

    I have been on vacation and very busy with work. But thank you for very much for your suggestions.

    I did cut open the oil filter but didn't find any carbon/plastic pieces in it nor any other suspect findings in the filter. The magnetic plug showed some collection of steel dust (is that a correct word?) after it was cleaned. No big pieces,only dust, and a little more than I would expect. See the Picture.

    The gearbox friction torque according to LMM 14.1 was measured and was it was very low, just on the edge of the acceptable value of 30Nm. In fact I measured it several times and did the calculation several times just to be sure it was that low and one time I saw 28Nm I think.

    As the engine now has 1000 hours the gearbox needs inspection. As I can't do this myself without the correct tools It has been agreed with the owner to take the aircraft to a Rotax Service center to have it done.

    Since my last post the engine has beginning to behave strangely.
    To begin with the engine had some rough running in the 2000-2400 rpm area, but only sometimes.
    Then the engine began to stall in this rpm area if the pilot didn't react with throttle response quick enough. It was here noted that the Carburetors were over-floating.
    The engine has become hard to start with a very rough start sequence, like the the engine is on the edge of firing back. Battery is fully charged.
    This aircraft has an 125Amp fuse on the wire to the starter and is has blown a couple of times.

    As I replaced the floats because of wear-spots and weight differences during 1000 hour service I thought that maybe I did something wrong. I inspected the floats and found 1 float to be 0,3g heavier that the others. I don't believe this can cause so much trouble but the owner wanted me to do a rebuild of the carburetors just to be sure there are no worn parts.
    This was done and every channel cleaned out with compressed air in the correct direction, float level adjusted to 0,5mm -0,1.

    I tried to start the engine and expected to run smoothly like it always do when I have done this. But no no.
    The engine wouldn't start and was close to backfire several times and start sequence was very rough. So rough that both carburetors were over-floating and eventually one of the overflow hoses blew off the carburetor.

    Now what?
    I'm going to measure the fuel pressure tomorrow, but I don't think this is the fault.

    Another thing I have noticed is that the during flight in power from full to about 5200 there is a kind of cracking sound from the engine/prop. I'm using a Bose A20 headset so All high pitch noises are gone but I can hear small distinct sounds. It sounds like a small prop blade stall or some "knocking" sound from the engine. It disappears when throttle is reduced to cruise bellow 5000 rpm.
    I own a similar aircraft with the same prop model but my engine/prop doesn't sound anything like this.
    Maybe I'm beginning to be paranoid but there are some warnings going off here.

    Any comments or suggestions is highly appreciated.

    Regards
    MOL
    20160813_123353s[2].jpg (You do not have access to download this file.)
      
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  • Re: Oil tank contaminated with big Carbon pieces

    by » 8 years ago

    Looking at the magnetic plug picture, something is up inside the engine . That is way too much filings on the magnetic plug.
    How many hours run time from when the magnetic plug was last inspected and cleaned ?

    Low friction torque in the gearbox was mentioned, a definite place to look.
      
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  • Re: Oil tank contaminated with big Carbon pieces

    by » 8 years ago

    The gearbox definitely needs to be done and I wouldn't run it any more until then. How can a vent tube off the carb blow off it should be an open hose? If this got clogged it would cause some of your problems. Once the engine is warm is it hard to turn over by hand at the prop?

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

      
    Report
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