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Unable to purge the system

in 912 / 914 Technical Questions 8 years ago
Hello Rotax owners.

I am new to this forum/list, and need some help from you experts. I purchased a used Rotax 912 uls engine, with only few hours flown. After completing my Zenith 701 building, I purged the oil system according to the video on this site. When I try to move the oil back into the oil reservoir, I never hear the gurgle sound, but only air hissing from the valve cover on number 3 cylinder, and oil leaking. I have installed new o-rings on all covers, so they should be normal seal.
I removed the heads and cylinders on number 1 and 3 and inspected the hydraulik valve lifters, and everything looked normal. No wear.
Can anyone give me any advise on what could be causing this problem?

Thank you in advance,
Johann G.

  • Re: Unable to purge the system

    by » 8 years ago

    Make sure nothing is blocking the return line. I was at Lockwood Aviation one day and they had just received an engine where the owner had forgotten to remove a plug and the pressure had forced an oil seal out if place. The engine was severely damaged from no oil flow/pressure.
      
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  • Re: Unable to purge the system

    by » 8 years ago

    It sounds like a crack in the valve cover or warped heads?
    Was the engine ever overheated? (loss of coolant)
      
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  • Re: Unable to purge the system

    by » 8 years ago

    Hello Rob and Garret.

    I do not know the history of this engine, other than the seller told me that it had been in a fire. So the overheating head reason seems very likely. I does also support the feeling I had when tightening the head and noticing that the heads on #1 and #3 are not aligning correctly. #2 and #4 look alright. Also I noticed that the head # 3 is darker that the others.
    So if this is the reason for the oil leak and no pressure to the oil tank, is there a remedy, other than spending #$4000 to buy 4 new heads?

    Best regards,
    Johann G.
    Iceland.
    Thank you said by: Andrew Dunning
      
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  • Re: Unable to purge the system

    by » 8 years ago

    There is a hardness test/procedure that Rotax has you/machine shop can do on the heads to test for overheating as a confirmation that they were overheated.
    Thank you said by: Andrew Dunning
      
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  • Re: Unable to purge the system

    by » 8 years ago

    The easy way to tell if your heads are overheated: remove the head )or put piston to TDC and compress the valve springs slightly). Then push on the rocker shaft; if you can move it by hand pressure it is OK, if you need a hammer to move it the heads are warped.
    Warped heads are not repairable: they lose their hardness and the valve seat can come out or be pounded into the head. Also the valve guide may be misaligned and the head will not make a good seal with the cylinder. All very bad issues.
    If the fire was that bad I would not trust the engine to be serviceable.
      
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