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My engine is a 912ULS with 1100 hours. I personally put the last 750 hours on it and it has not been abused. Oil, and filter are changed at 50 hrs, plugs at 100, auto fuel only. On the last 2 leak down tests cylinder 3 was low 73/80. Those tests the engine was cold for the test so I ran the engine and retested it immediately and got 78/80. Today at 100 hr check I came in from a flight and tested within 15 minutes of shutdown and am again getting 73/80 on #3. My second problem possibly related is oil usage about 1/2 -3/4 oz per hour. The engine seems to run fine makes good power and gets very good mileage. The engine is extremely clean so it's not leaking and the plugs all look good. I would expect #3 plug to look different if oil was being used in that cylinder. What action should I take?


Walt

my blog; waltsrv12.com

  • Re: leak down low on one cylinder / oil usage

    by » 2 weeks ago


    I'd say you're doing pretty good compared to say - Lycoming uses one quart oil every few hours.  My 912ULS has 850TT running 93E10 auto fuel and uses a liter (bottle) of oil every 75 hour oil change interval.  I use Mobil 1 Racing 4T Full Synthetic Motorcycle Oil 10W-40.  To answer your question... I would just monitor oil consumption for now.  Perhaps borescope the cylinders and look for inconsistency...


  • Re: leak down low on one cylinder / oil usage

    by » 2 weeks ago


    Hi Walt! On the basis of your description one gets the positive impression that you engine is doing fine when warm. That’s the state it is in when you’re up in the air. Keep an eye on oil consumption and have fun, I‘d say. Compression and leak down test results depend on temperature. Beware not to over-judge a single indication.


  • Re: leak down low on one cylinder / oil usage

    by » 2 weeks ago


    I had an increasing oil burn in my previous 912UL. It turned out to be the piston oil control rings. The springs behind the rings had worn grooves in the back of the rings which prevented them from pushing tightly against the cylinders. Unfortunately it's only possible to see if this if you remove the cylinders. I didn't have any other symptoms other than the ongoing oil consumption. The plugs always looked good.


  • Re: leak down low on one cylinder / oil usage

    by » 2 weeks ago


    If you are really burning through oil your exhaust should have some smoke and or the exhaust pipe may not be a dry coating, but maybe a bit oily residue. If you have a leak or burning oil then that residue should be all over the bottom of the plane. If your oil tank is too full it can come out the vent tube and be all over the bottom. Your oil level check can lie to you. It may not be dead on every oil level check. I'd run it a bit longer and keep an eye on it. 7 psi drop isn't horrendous, but I agree it's usually higher within 1-4 psi.


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


  • Re: leak down low on one cylinder / oil usage

    by » 2 weeks ago


    Roger Lee wrote:

    If you are really burning through oil your exhaust should have some smoke and or the exhaust pipe may not be a dry coating, but maybe a bit oily residue. If you have a leak or burning oil then that residue should be all over the bottom of the plane. If your oil tank is too full it can come out the vent tube and be all over the bottom. Your oil level check can lie to you. It may not be dead on every oil level check. I'd run it a bit longer and keep an eye on it. 7 psi drop isn't horrendous, but I agree it's usually higher within 1-4 psi.

    Roger,

    At this low rate of burn I wouldn't expect to see it as smoke in the exhaust. The exhaust pipe is not oily, it is dry. The bottom of the plane is clean and the oil level is checked in my hanger each time with the plane in the same marked location. The bore scope pics show #3 with more deposit on the piston when compared to the others.

     


    Walt

    my blog; waltsrv12.com


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