912 using oil

[ackselle]

HuDuGuru.... you are absolutely correct!

I re-read my log books.... my mistake, I misinterpreted the entry .... Oct , 2010 "...lapped valves....reassembled and resealed engine...". I mistook "resealed" as putting it all back together.

So...the puzzle continues...since I bought the plane it has used oil at a very consistent rate.... approx 4 oz every 3-4 engine hours. Compression is great, differential pressure is great (see below). No leaks whatsoever. Engine runs great!

Spark plugs from cylinders 1 and 2 are dark, but not fouled, cylinders 3 and 4 are nicely tanned. Seems to indicate valve seals in cyls 1 and 2..... or something more insidious.

Any ideas?

[WWhunter]

I will have to say we are having similar issues. Mine does essentially the same. I will have to double check which cylinders (plugs) are 'black' but I seem to recall it always being two specific cylinders. No leaks anywhere and the oil usage is unacceptable.

[jamesmil]

hi guys, just read the whole thread on your 912 oil use and i think you might need to look at the rotax forum as there is an ad about oil use posted. what is happing to some engins is a small hole will develope under a valve spring that is over an intake runner and it will pull oil into the engin that way. holp this helps

[ackselle]

Thanks James..... I'd like it to be that simple.... but my engine does not fall into the serial number range of the units affected.

[HuDuGuru]

The engine had over 1200 hours on it at the time and by the looks of it someone had run 100LL for a very long time without using Decalin or the proper oil.

Don’t quote me on this next part since my memory is a little foggy from a few years ago and I wasn’t paying close attention. I believe the cylinders were removed along with the pistons and rings to clean the carbon and lead build up in the ring groves, I seem to remember one cylinder had a stuck ring.

Having good compression doesn’t mean the oil control rings are in good shape. Doing a valve job without replacing the rings and honing the cylinders on a semi tired engine can also cause increased oil usage.

I also seem to remember an SB issued for that engine regarding the valve retainers. I would go through the logs very carefully and if you don’t see an entry for work that should have been completed, I would consider it “not done”.

[ackselle]

Thanks HuDuGuru,

Oil control rings..... that's what I've thought for a while now (see my original post). I'm guessing that's what it will be. I'll keep the group posted.

Cheers,
Ackselle

[ackselle]

HuDuGuru.... the SB you are referring to is SB912-022... and it pertains to Single Valve Springs..... this one has the dual springs. Thanks for the heads up!

Cheers,
Ackselle

[ackselle]

Update..... I've replaced all the rings in my engine. Got it all back together and running.....and I'll keep you all posted regarding oil consumption. My guess is I've fixed the problem....take a look at the picture of one of the oil rings below......they all looked like this. The top 2 rings on each piston were near perfect. Gap was .016 on all rings and the new gaps are all .015. BUT.... The oil control rings were a mess to put it mildly. The "spring" part of the ring was no longer a spring, but rather it was completely brittle. They were completely gummed up as HuDuGuru thought they would be. The pictures say it all.

The cylinders are in great condition....they all look like new.

[WWhunter]

Ackselle,
I sure hope you resolved your oil usage issue! I have never dealt with the 912 before so am a neophyte with their workings or teardown procedures. Was this ring replacement difficult?
The other issue I may have is the pistons in my engine are the ExtraPerformance 95HP replacement ones and I can not find if they use stock rings or an exclusive set.
Thanks,
Keith

[ackselle]

Changing the rings was a relatively simple task. I followed the ROTAX Maintenance manual to a tee, which was very helpful. I'd guess I spent about 5-6 hours (2 evenings) changing the rings and reassembling.

The one difficult task was trying to get the pistons/rings back into the cylinders....the ring compressor simply got in the way....so I used my fingers and thumbs..... got them all cut up!

Regarding the Extra pistons.... the Extra web site says they use the stock piston rings (http://www.craftworks.biz/pistonsite/6318.htm).

Cheers,
Ackselle