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I am adding a thermostasis kit to my 912ULS that has 850 hours run time. I will be replacing 4 oil lines. Will I need to pull the  valve covers and test the hydraulic valve tappets for air?

I plan on pressurizing the oil tank and pulling the prop through until I see pressure. Just wasn't sure about the tappets since this is an already running engine. Any other suggestions?

  • Re: purge oil per SI-912-018

    by » 7 months ago


    In as much as you will be pumping the Air in the Oil hoses through the engine and past the Tappets, retesting would be indicated.
    If you would like to avoid the situation, remove, or at least loosen, the Oil Hose connector at the input to the oil pump.
    Without Cranking the engine, pressurize the Oil Tank until you see oil flowing out the connector at the Oil Pump. 
    At this point, the Oil Hoses are full,  Tighten the connector and crank until you see Oil Pressure.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


    Thank you said by: Walt

  • Re: purge oil per SI-912-018

    by » 7 months ago


    Bill Hertzel wrote:

    In as much as you will be pumping the Air in the Oil hoses through the engine and past the Tappets, retesting would be indicated.
    If you would like to avoid the situation, remove, or at least loosen, the Oil Hose connector at the input to the oil pump.
    Without Cranking the engine, pressurize the Oil Tank until you see oil flowing out the connector at the Oil Pump. 
    At this point, the Oil Hoses are full,  Tighten the connector and crank until you see Oil Pressure.

    Thanks Bill, I did as you advised and added one more step per Roger Lee by hand propping without plugs to get 40 pounds of oil pressure, let it sit a few minutes and repeated the hand propping. I started it up and no had strange noises. Considering that Rotax's fix for a flat lifter is to run the engine for a few minutes (up to 3 times), It doesn't seem to be harmful to run it. In my experience with cars a flat lifter causes that cylinder to produce less power. In a Rotax that would equate to vibration, a clue to stop it and recheck.


  • Re: purge oil per SI-912-018

    by » 7 months ago


    Hi Walt

    I would not like to compare an engine with a propeller to one that has a clutch (or torque converter) as they load the engine very differently.  We do not have the ability to remove the load as you do in a car so it is always "in gear"so to speak.  The propeller also generates a significant noise that damps any lifter tick or clicking you might have heard in your old Chevy or Ford (let's not talk Mopars they can have other issues) An auto engine at idle with no load, not driving, has very limited pressure on the crank rods as one that is moving off at the intersection.  We all agree that the possibility of lifter unloading is rare but we also know in some conditions it can lead to failures.  We have ample physical evidence of this with failed lifters and cams along with failed lower con-rod bushings.  If we have too much air introduced the condition might not occur right away but over time it can lead to a failure.  If you ever see or heard of a lower con-rod failure on a Rotax check to see which rod bearing it is....good chance it is number 1 lower bearing.  This is actually predictable and tells us it did not have a purging at the time of initial setup or at points of its life where someone simply ran it up waiting for the engine to clear the air on its own.  The number 1 rod bearing when we trace the dry sump oil circuit is the very last port that is in the system...so it runs without sufficient lube the longest.  In the same way lifters can be deprived of oil long enough that they fail to pump up and this leads to loss of control between the lifter and the cam lobe.  Once damaged there is little hope of recovery, it just gets worse.  

    I agree with Bill in that at least take the time to fill the suction line and be sure that the oil pump and filter are full.  Turning the engine after by hand, in the correct direction, is also a good idea.  I personally like to leave the plugs in as it takes crankcase pressure to push the oil out of the case and back into the oil tank.  Without the plugs I dont want too much oil pooling in the crankcase.  Should you do this too much the suction tube inside the oil tank may unport and you could inadvertently pick up air...that would be a waste of time.  

    The Rotax purge for new engines as to the lifters is to check them after a short test run.  If you have one not pumping up it may be you just did not get all the air out of the system so they ask you to repeat it.  It was never meant to be a full on power run.  The lift on a Rotax cam is very small and we will never get to a point in such a short test run to notice any power loss.  if you're that far up the power band I would get rather worried.  

     

    Cheers


  • Re: purge oil per SI-912-018

    by » 7 months ago


    Hi Cheers,

    When I said that a flat lifter would cause the cylinder to produce less power. I was not referring to the whole engine losing power, just the affected cylinder. In the case of the 912 a cylinder that is not making the same power as the others would cause a noticeable vibration especially at the 3500 RPM for 5 minutes Rotax recommends for the test run.

    Walt

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