oil in cylinder on a rotax 912

[dalords]

Has anyone ran into the situation of having oil in a cylinder after it has been sitting for awhile? Didn't get much of a chance to fly this winter but did go out and at least run the plane every month. Today when to go start the plane and when I went to burp the engine, it locked up as I pulled the prop through. I pulled the spark plugs and turned the prop and oil came squirting out of the #4 cylinder. I would guess about 8 ounces or more? Any thoughts

[Floog]

Only a WAG: Oil in the head area (for rocker arm lubrication) is getting into the cylinder through a worn valve guide. Have you ever seen smoke when running? How many hours on the engine? Good luck.

[avidflyer]

I believe that sometimes a Rotax 912 will transfer oil from the tank to the engine and it can then leak into the cylinders. That was more likely with a higher mounted oil tank, and I think that is why Kitfox started mounting the oil tank on the side of the engine instead of up high behind the engine. I have yet to run my 912, so I'm just answering from memory of what I've read. I'm sure others with more experience will chime in. Jim Chuk

[Av8r3400]

This is not an uncommon problem with the high mounted oil tank.

It is very important to be in the habit of pulling the prop through at least a few turns before starting. The problem is that the oil can syphon from the tank to the engine if the filter has a bad or no check valve. The newest part number filter from Rotax solves this problem with a very effective check valve built in.

Aftermarket, non-Rotax and older Rotax filters usually don't have this valve which can lead to this problem. The non-Rotax filters also have a lower bypass pressure which leads to them not filtering most of the time.

[DesertFox4]

Had that happen to me twice fom sitting too long. Once on my model 3 and again on my 4. Newer models may have less susceptibility with their oil reservoirs mounted much lower in relation to the crankshaft level.

As Av8r3400 described, the early models when equipped with a 912, had no room except behind and higher up on the motor mount for that oil reservoir.
Over time oil could transfer very slowly into the cylinders.
As stated, always pull the prop through in direction of engine rotaion only before engaging the starter.

If you get a lock up, do just what you did and remove the bottom spark plugs and move the oil out by rotating the prop slowly in the direction of engine rotation only.
You may have a smokey start-up after but that should quickly clear up after warm up with no harm done.

I just returned from the airport and slowly pulled my 912 uls through 100 blades to get it to burp. It's been unusually windy here so haven't flown for 2 weeks. I concure with Av8r3400 that the Rotax oil filters help this condition.

[dalords]

Thanks everyone you have been a big help.

[Peteohms]

Mine got oil in the cyl's when I first bought it. It had been sitting awhile. After I flew it awhile it quit doing that. I've flown nearly 900 hours since with no problems.