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