Oil burn/usage

by anthony grantham in General Tech Discussion 8 years ago

Hi there everyone
as a newby i have a few questions if someone could help
I purchased a 912ULS fitted to a gyrocopter here in Australia
firstly have i been told correctly that a 912ULS is a 100 HP ?
enj no 5652284,i have been told its a 2009 build with 123.5 hrs
i have notice that i seems to consume a lot of oil
pressure is ok as per the maintain manual,there is no leaks or weeping
but the exhaust outlet is black and sootie in colour, spark plugs are
medium grey on all 4 pots,it would use about 100 mls every 1.5 hrs at cruse
4800/4900rpm,the blow by catch bottle is clean and empty
any comments or advice would be appreciated,it starts and runs like a roo
but the oil usage has me in a pickle

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Re: Oil burn/usage

by Roger Lee » 8 years ago

Roger Lee

126 5.13k 4.55k

Hi Anthony,

Yes the 912ULS is 100 HP.
As far as the build date Rob will have to check that out, but sounds in the ballpark.
Try to keep your cruise rpm at least 5000+ rpm.

As far as oil use I hear this all the time and it is very rarely the case. Most times it is sitting in the bottom of the crankcase. Rotax the prop until you hear the oil tank gurgle a time or two and then check the oil. This is not an exact science as some think and the level can still be off some. It's just a good approximation. I do doubt your engine is really using oil over a false level reading. If you don't have an oily exhaust, oily spark plugs, leaks on the engine, oil all over the bottom of the plane you aren't using oil. A black dry soot in the exhaust can be very normal and will depends some on how much idling you do, but it should be dry. Plugs can have black dry soot on them from unequal air intake and idling.
But you should not have oil on the bottom of the plane if it is a tractor engine or all over the prop as a pusher. You should not have oil from leaks on the engine.

p.s.
If there is a roo in the plane get rid of him. They make a mess. :silly:

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

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Re: Oil burn/usage

by Kevin Stewart » 8 years ago

Kevin Stewart

5 184 0

Hi Anthony,

I had a similar problem which was assumed to be oil not returning to the tank and therefore giving an incorrect reading on the dip stick. I can say for sure that the oil consumption was definitely real, otherwise I would have filled the whole engine with the amount of oil that I poured in over the last year!

Anyway, I think that I might have got to the bottom of the issue. My problems all started after I had the engine rebuilt. When I reinstalled it I routed the oil return pipe differently to how it was before I removed it. It passed over a part of the engine mount rather than under it. I have now re-routed the pipe back to its original position and so far this year I have had no oil consumption.

I was put onto this by someone who works on motorcycle engines who had seen this problem with a new engine when the oil return was partially blocked causing there to be too much oil in the crankcase. The theory was that my return pipe went soft in the heat and pressed against the mounting frame restricted the flow. Then, with too much oil around the crank, too much was being splashed into the cylinders increasing the oil burn.

It sounds pretty far fetched to me but the evidence seems fairly clear cut. If I can do a few more hours without any oil burn then I think I will declare the problem solved :-)

You may therefore want to check your pipe routing or check for blockages in the pipe or banjo joint.

Good luck!

Kevin

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Re: Oil burn/usage

by Roger Lee » 8 years ago

Roger Lee

126 5.13k 4.55k

You can have oil consumption, but it has to show up somewhere. If you are using oil and don't know where it is going then that's a problem. If the oil return l;ine was blocked or reduced flow far enough then oil would build in the crankcase, but that means the level in the tank would be down low or even off the stick, but that also means you couldn't burp it or it would take forever.

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

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Re: Oil burn/usage

by Rob Seaton » 8 years ago

Rob Seaton

3 1.32k 240

Anthony,
5652284 was manufactured Nox 2008.
Considering you have evidence of burning oil (sooty tailpipe) have you tried a differential compression test?
What values are you getting? anything lower than 70/80 psi is a concern.
Besides the values that test can tell you a lot about your valves and piston ring condition (listen in the exhaust tailpipe, carbs and oil tank for excessive blow-by)
Maybe your rings are leaded up/stuck (from avgas)?
Rob

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Re: Oil burn/usage

by Roger Sheridan » 7 years ago

Roger Sheridan

0 2 0

Dear All, esp Anthony & Kevin,

I have just read both your posts on excessive oil consumption as I appear to be suffering from a similar condition.

Rotax 912UL, Sn 4401447, recently rebuilt with new sprag, cam & tappets.
Oil pump spring was shimmed to increase oil pressure.

40 smooth hours since rebuild, 500 total.

Casing, exhaust & belly are dry, breather bottle not filling, but I do get a small weep from the breather bottle outlet that was not there before the rebuild. The amount seems very small & can be wiped away with a finger - however, I suppose that a mist of oil could be departing via the breather bottle outlet & not depositing on the skin.

Oil return pipe is not squashed, nor routing changed.

Engine gurgles after about 10 blades, but the loss is cumulative & not down to gurgling variations.

I estimate losing 100ml / hr.

Did you guys confirm cause & eliminate your problem?
Any suggestions gratefully received.

Best regards,

Roger

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