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Purging the oilsystem

in 912 / 914 Technical Questions 13 years ago
Dear Rotax Owner,

I have made several oil purging during 5 years according to SI-912-018 and video on this site.
After 20-30 turn the pressure build up to normal 3.5 bar (35 on Flydat).
One thing surprise me: I hardly never see any oil coming out from the engine oil output (ie open hose
to oil tank marked IN). I did an extra 50 turn today but still no oil from the open oil hose.
If the oil pressure builds up there must be oil coming in?? and oil going out (same amount)??

Please let me know how it should work. This driving me nuts.

Best regards
Stephan
LN-STE 912ULS

  • Re: Purging the oilsystem

    by » 13 years ago

    Hi All,

    Don't get oil pressure and volume during a purge confused. You can have pressure, but not do a purge throughout the system. The oil pressure sending unit comes off right after the filter on the other side of the pump housing. Make sure you rotate the prop enough turns to pressure flow the oil throughout the engine. The pressure from the compressor should be between 5-15 psi. I tend to use 10 psi. I always hang the oil tank inlet line into a catch tub and rotate the prop 60-80 times with a little speed (good aerobic workout) until I get some oil coming out of that line. It won't be much oil or a fast flow, but you should see some return to do a good job. It is a must to get oil in and air out of the lifters and other oil lubricated critical parts. Failure to do this can cause metal scuffing, over heated parts and failed parts that would need to be replaced.
    There is a video of this purge here on our forum.

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

    Thank you said by: Don Hudgeon
      
    Report

  • Re: Purging the oilsystem

    by » 13 years ago

    The oil pressure can build up, but only a small amount will be squeezed out into the crankcase, most will probably come from the rockers, but at very low revs it won't be much. If there were big clearances on the crankshaft and camshaft bearing and tappets, then there wouldn't be much pressure, but lots of oil coming out of the return tube. The oil goes from the pump, through the filter and then around the engine, the oil pressure is then measured at the end of the oil way, the furthest point from the filter and not just after the filter. Fig 79-3 of the Heavy Maintenance Manual shows this.

    Cheers Mark

    Hi All,

    Don't get oil pressure and volume during a purge confused. You can have pressure, but not do a purge throughout the system. The oil pressure sending unit comes off right after the filter on the other side of the pump housing. Make sure you rotate the prop enough turns to pressure flow the oil throughout the engine. The pressure from the compressor should be between 5-15 psi. I tend to use 10 psi. I hang the oil tank inlet line into a catch tub and rotate the prop 60-80 times with a little speed (goalwaysod aerobic workout) until I get some oil coming out of that line. It won't be much oil or a fast flow, but you should see some return to do a good job. It is a must to get oil in and air out of the lifters and other oil lubricated critical parts. Failure to do this can cause metal scuffing, over heated parts and failed parts that would need to be replaced.
    There is a video of this purge here on our forum.
    Thank you said by: Don Hudgeon, YEN NIEN YU
      
    Report

  • Re: Purging the oilsystem

    by » 13 years ago

    Hi

    Thanks for information. That makes sense. I will have a good aerobic workout this afternoon :)

    Best regards
    Stephan
      
    Report

  • Re: Purging the oilsystem

    by » 13 years ago

    Hi Roger&Mark
    I have yet to do a "purge" because I have not ever emptied the oil tank or broken a line BUT when the time comes, would it not be OK to turn the engine over on the starter (Modules OFF)a few bursts until the oil flowed. Would the higher starter crank speed do damage or is it better to pull through by hand? I have been "starter cranking" it when I do an oil change. Is this not advised. I realize some ignition systems are not set up this way but if they are, is it OK?
    Thanks for your input.
    Cheers
    Don
      
    Report

  • Re: Purging the oilsystem

    by » 13 years ago

    Hi Don

    All the moving parts in the engine rely on oil to keep them apart, otherwise they will wear out very quickly. Things like the main shells on the crankshaft are coated with white metal which is very soft, and they rely on oil pressure to keep them separate from the crankshaft bearing surface. If there is no oil pressure between the two then the white metal bearing surface will get damaged and wear away very quickly. Then you are looking at several Thousand pounds to have the engine stripped and new shells fitted. On every compression stroke as you turn the engine over you are putting load on the bearing, and by removing the spark plug you are reducing the compression and the load and so reducing the chance of premature and unnecessary wear. Turning the engine over with the starter motor is probably ok, although I would recommend spinning the prop by hand. A nice steady pace is all that is needed, I don't think you will gain anything by spinning the prop faster but I may be wrong.

    All I would say is don't try and rush the job, take your time, do it as correctly as you can, and enjoy it.

    I am by no stretch of the imagination an expert on these things, it is just a basic understanding and a bit of common sense.

    I hope this is of some help.

    Cheers Mark
    Thank you said by: Don Hudgeon, YEN NIEN YU
      
    Report
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