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won't burp

in 912 / 914 Technical Questions 9 years ago
I have an otherwise good running 912ul. A few weeks ago I tried to burp it and it would never burp, not even after 100 blades. Checked the oil and it barely touches the stick. I know for sure it's full of oil. Oil pressure comes right up pulling it by hand. I get 50lbs of oil pressure with the starter. It idles with 70 lbs when cold. After running it a few minutes the oil level checks full on the dip stick. I have a friend who has had all the Rotax schools and he doesn't have a clue either. The engine is very low time. We can't find any leaks. Nothing has been apart. Any ideas? Thanks, James Thomas

  • Re: won't burp

    by » 9 years ago

    Hi James,
    This may be a 1-2 time thing or happen with some frequency as each engine setup is a little different. Oil tank height in relation to the engine may or may not be playing a part here and if you are using the old style oil filter verses the new.

    I have seen this a few times where for some reason (maybe the oil tank is mounted too high and siphons back to the case) the crankcase has 1-1.5 qts. of oil in it and the tank looks low. So you would have to crank the prop a long time to get it all back out since it's a slow process. I have seen people swear their oil level is low and add oil then start it and have oil all over the ground. If you run into this extra low situation just realize the oil level check by burping can lead you down the wrong path. If you have a situation like you had the right thing to do was to look for any leaks and if nothing is found start it up after you have tried to burp it and then check the oil level again.

    Hopefully this will be a limited scenario.


    Maybe Rob or Conrad can chime in a give a better synopsis.

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

      
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  • Re: won't burp

    by » 9 years ago

    How does the compression feel as you pull the prop through? If the rings are stuck or valves not seating properly then burping can be a long process.
    Try a differential or direct compression test and see if your numbers are low. Maybe it just needs a good hard run if you have been babying it.
    Rob
      
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  • Re: won't burp

    by » 9 years ago

    A technique I use to quickly burp the engine is to turn the prop slowly to each compression stroke and turn it slowly maintaining pressure during the the time you feel the cylinder compression. Then quickly rotate it to the next compression cycle and slowly rotate thru this, and so on. What this does is to maximize the time you feel compression and minimize the time you don't. Only during compression are you leaking pressure past the rings and into the crankcase to blow oil back to the tank. This method also minimizes your manual turning of the oil pump that sucks oil out of the tank and back to the engine. I have found that doing it this way reduces the number of prop blades by about 30%, and is much easier than madly turning the prop as fast as you can.

    I didn't invent this technique; it was suggested by someone on this forum I think.
      
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  • Re: won't burp

    by » 9 years ago

    I prefer that technique as well. That exactly what they are trying to say in the Owners Manual.
    They just need to reword "remove oil tank cover" to "remove oil tank cap"

    oilcheck.jpg (You do not have access to download this file.)
      
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  • Re: won't burp

    by » 9 years ago

    Hi Rob,
    I don't think his problem is prop rotation speed. His post says his oil level is down off the stick and goes to full after a run. Why do you think all that oil is draining back to the case?

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

      
    Report
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