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914 oil use

in 912 / 914 Technical Questions 13 years ago
HI ALL
Still having trouble, oil in intercooler, loosing 200ml per hour, flushed all the oil lines
out, no luck, seems to happen during flight . Could it be going past the seal in the turbo.
Local rotax expert assures me that not likely. Checked the oil return back to the tank ,plenty of oil flow.
Run out of ideas

Greg Regan

  • Re: 914 oil use

    by » 13 years ago

    Hi Greg,
    Your Rotax guy is right; it is not likely a turbo problem. It is likely an oil system problem but you need to determine what system is at fault:
    Scavenge system: if the oil is being consumed during engine operation (continuous blue smoke) your scavenge system is at fault. You need to remove the turbo sump and inspect for coked oil flakes, remove the banjo bolts at the scavenge pump and oil tank and check for blockages and clean out the hoses. Sounds like you have already eliminated this. If you find flakes of coked oil you need to run a longer cool-down period and/or get better oil.
    Oil delivery system: if the turbo compressor side has oil in it (smoke at start-up but dissipates over time) you need to re-work your check valve: remove the special banjo bolt, spring and ball from the top of the turbo, place the banjo on a hard surface (vise/anvil) put the ball in the end of the bolt and give it a good rap with a small ball-peen hammer. Inspect the sealing surface closely; even a small imperfection will cause a leak. Replace the ball with new part, clean all the parts and reassemble. You need to clean out the oil from the compressor side, intercooler and airbox to finish the job and confirm the success of your work. This can be a lot of work but if you don’t do a thorough job you will not know for sure if you have fixed it or not. Run the engine and let it sit overnight; if the compressor side fills with oil again the check valve (special banjo/ball & spring) should be re-worked again or replaced with new parts. Do not modify the spring to force the check valve closed; you will starve the turbo of oil during the cool-down (high oil temps and low RPM can cause the oil pressure to drop below the check valve “closing” point)
      
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  • Re: 914 oil use

    by » 13 years ago

    If I remove the sump plate on the bottom of the turbo after flying and cool down and wait to see how much oil drains that should tell if its leaking past the check valve How much will leak normally? How much is too much?
    Greg
      
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  • Re: 914 oil use

    by » 13 years ago

    I have never tried that, no idea. I know oil will come out of an open engine port for years...
      
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  • Re: 914 oil use

    by » 13 years ago

    Perhaps I will try a different approach, If you take of the sump cover and if the check valve is working there should be hardly any oil in the cover as the scavenge pump will have returned it to the tank. Not sure if I am thinking straight Thanks for your input rob.
      
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  • Re: 914 oil use

    by » 13 years ago

    I think that would just be more work. Just re-work the check valve and check the compressor section a day later (pop the rubber intake hose off and look for a pool of oil inside)
      
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