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Problem purging 912UL oil system

in 912 / 914 Technical Questions 8 years ago
I have just replaced all the oil lines and conducted what I thought was the correct purging procedure, but no oil is returning to the container. I have done the following:

1. Removed the return (In) pipe from the tank.
2. Capped 'In' pipe on tank.
3. Connected additional pipe to return pipe and placed end in container.
4. Top 4 spark plugs removed.
5. Oil tank breather pipe conected to foot pump.
6. System pressurised to approximately 5 psi
7. Propeller rotated quickly by hand for approximately 40 rotations.
8. Oil pressure indicated 2.5 - 3 bar.
9. Process repeated three times with maximum shown as 4.5 bar.

All sounds good, but I do not understand why no oil is returning to the container. Is it possible I have not given it long enough and should do additional rotations? Could it be that I am not getting enough pressure into the tank? Could it be the oil pump?

Any ideas or suggestions would be greatly appreciated.

Kind regards

Gordon Grant

Europa Classic TriGear Rotax 912UL

  • Re: Problem purging 912UL oil system

    by » 8 years ago

    You need all the spark plugs installed it piston blow-by that pressurizes the crankcase to force the oil back to the tank.
      
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  • Re: Problem purging 912UL oil system

    by » 8 years ago

    Did you watch the video on oil purging?
      
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  • Re: Problem purging 912UL oil system

    by » 8 years ago

    You can purge with the plugs in or out. I've seen it done both ways. So long as the return hose is hanging in the downward position oil should drool out. If the plugs are in it will pressure the oil out the case. I think the problem is you said you're using a foot pump? If so you need to use a compressor and try 10 psi with some volume vs your 5 psi. Volume here is more a key than pressure by itself. You can use between 5-15 psi. If you leave the plugs in you rotate the prop slower because of the pressure in the cylinders. If they are out I'll rotate at a rate of 90 revolutions per minute. Then since I'm old I call 911 and get some Oxygen before I rotate one more minute. :P :lol:
    The oil pump is a positive pressure rotary pump and so long as something is pushing oil in (your air pressure) and the carnk is turning (rotating the prop) then oil gets moved through the system.
    I usually see 50-55 psi on the oil pressure guage in the cockpit. Since I'm paranoid of having a bad purge I do a purge twice. Cheap insurance for just 1-2 minutes of work. Sometimes oil comes out and sometimes not, but it has always been good. Check your tappets under the valve cover like it shows in the video. If you do this purge a couple of times and get no oil then start the engine normally. You should have oil pressure immediately. Let it run a few minutes then shut it down and check the oil level.

    p.s.
    When you do a purge have a little extra oil in the tank so as the oil fills the hoses and the like the oil level in the tank won't get too low and possibly inject air.

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

    Thank you said by: Gordon Grant
      
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  • Re: Problem purging 912UL oil system

    by » 8 years ago

    Thanks for the reply Roger,

    I think you have probably hit the nail on the head regarding pressurising the system and the foot pump was not man enough for the job. I will get a compressor onto the job. The other good point you have made is making sure the return pipe is dangling down. Having just installed the new pipes into my very cramped Europa I assumed the return oil would have sufficient pressure to reach the top of the pipe and I fitted an extension pipe from there down to the container. Obviously I will have to drop the pipe down and then have another battle to re-route it, but if this does the job it will be worth it. One final point: the way my oil tank is mounted I can not get access to no 3 rocker cover without removing it, and after that I have to purge again. Bit of a Catch 22 situation!

    Anyway, thanks for the advice and of advancing years I am off to order a canister of oxygen!

    Kind regards

    Gordon
      
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  • Re: Problem purging 912UL oil system

    by » 8 years ago

    If all you have to do is remove the tank you won't have to purge again. When you remove the fitting on top of the tank put a rubber plug in them. So long as no oil leaves the hose it won't make any difference. The reasoning here is when you do a normal oil change and remove the bottom oil tank plug all the oil drains out and that includes everything up to an including those fittings. If you take those fittings off then no oil comes out other than a drop or two unless you lower the hose fitting downward. So long as it is kept pointing up the oil stays in the hose. Then when you put them back on and the plugs are in just rotate the prop to fill any voids like you would do in a normal oil change. Your oil filter is empty when you put a new one on, but you fill it by rotating the prop.


    p.s.
    When I pull tanks to clean them (especially with 100LL users) I never do a purge. I remove the fitting and put a rubber plug in it. I don't lose any oil. Then I put the tank back in place, fill with oil, replace the oil lines and rotate the prop to fill the filter and any hose voids. It's done well for 20 years.

    p.s.s.
    Don't forget to remove the rubber plugs. I actually have red cordage about 4" long on each one as a red flag.

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

      
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