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Hi, new here. My 2005 912ULS has a low oil pressre when hot. Cold its around 4-5 bar, but once the engine is at operating temperature I have 2.0-2.5 bar at 5000rpm. At the same time the resistance to turning the prob (barping the engine) is quite a bit higher when the engine is hot.

The (still old) sensor has been taken out and checked and it is 100% correct. The gauge, essentially a resistance meter, has also been taken out and also is 100% correct.

In connection with this I was told that these old engines suffer from a potential problem, and that is lI believe wear and tear at the middle crankshaft bearing resulting in lower clearances (and tus higher friction) when hot due to issues with the old crankcases blocking an oil line to the middle crankshaft bearing. rotax specifies a max torque or 150NM when the engine is hot with the spark plugs removed to check for this, my engine has only 70-80NM when hot with the spark plugs removed (much more with the spark plugs in, so seems like good compression?).

So now I am lost as to the cause for the low oil pressure?

Someone else told me the pressure can be increased in the oil pump? Is this correct and if yes where and how?

Thanks for helping me.

Joe

  • Re: How to increase oil pressure?

    by » one month ago


    Your engine is a little older than the ones that had crankcase fretting and a hot engine is harder to turn by hand than a cold one.

    After the engine is warm and you advance the throttle and then bring it back does the oil pressure get lower when you advance the throttle and then go back up again when you return to idle? This type of low oil pressure could be caused by a poor ground wire. You may have a ground, but a poor one. To test it pop the panel out and use a wire with an alligator clip on it and hook one end to a known good ground and the other to your guage. The other thing that causes it to fluctuate is a sensor starting to go bad. If it's an original oil pressure sender I would definitely replace it. I would replace the oil pressure sender if it sin't a poor ground. This is the #1 cause of pressure issues for the average person. Don't look for exoctic issues because it usually a simple common cause and fix.

    The next easy step to take iwould be to put a new oil pressure regulator spring in and get rid of the ballbearing and put the newer style mushroom pressure regulator in especially if these are originals. Just takes a few minutes to do this. It's the plug that should be safety wired under the oil filter on the bottom of the pump.

    The oil pressure can be raised, but I highly advise against using a shim until everything has been ruled out. You almost never need to take this step and many who have failed to do COMPLETE diagnostics do raise the pressure and then unbeknownst to them it's actually above max because they never found the original problem and tried to put a bandaid on it.


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-574-1080 Home (TRY HOME FIRST)
    520-349-7056 Cell

  • Re: How to increase oil pressure?

    by » one month ago


    Roger,

    thanks!

    As to your first question: no the oilpressure is 2.0-2.5 at 5000 rpm and a bit less at lower rpms.

    Thanks for the tip with changing the spring etc. Is there a Rotax part-# for the "mushroom" type valve? then I will try that first and only add the shim if it's still not better.

    I also will do the complete 5 year rubber replacement, which after 15 years is more than overdue, in in the course of this will look at the oil pump as well.

    I also have never taken the carbs apart, all I did is renew the rubber flansh several years ago and balanced them every 200hrs or so. I now have 750hrs on the engine and am a bit hesitant to take the carbs apart, they run just fine now....

    Again thanks

    Joe


  • Re: How to increase oil pressure?

    by » one month ago


    GOOD advise roger . On my 912 ULS wIth similarité problem, new spring and mushroom plug fix the problem


  • Re: How to increase oil pressure?

    by » one month ago


    https://www.cps-parts.com/catalog/rtxpages/912914oilpump2.php 

     

    You want #41 mushroom and #3 spring.

    I would replace my oil pressure sender if it's fairly old.


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-574-1080 Home (TRY HOME FIRST)
    520-349-7056 Cell

  • Re: How to increase oil pressure?

    by » one month ago


    Excellent advice by Roger Lee.

    His advice also fixed my low oil pressure problem (2006 - 912 ULS).

    Thank you again, Roger!


    Bill Ince
    CTSW (E-LSA)
    Retired Heavy Equipment Operator


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