Oil in Cylinder

[Robert Eilers]

I pulled my plugs to clean and gap in preparation for the annual inspection. I found the bottom plug of the number #1 cylinder soaked in oil. Turning the plug upside down oil would drip from the cavity. While I cleaned up the plugs, oil dripped from the empty bottom spark plug oil of the number one cylinder. Is there reason to start freaking out? The engine has been running, good oil burn, and has 200 hrs on a 2003 overhaul. Most of the hours in the past year.

[Bruce Fenstermacher]

I would note the oil in the plug, replace it and continue to run it unless there was some indication that something was wrong IE low compression or oil fouled plug.

[davevramp]

A wet cylinder is something to be watched. Oil in the combustion chamber reduces the octane of the fuel. This is not the time to use car gas. The oil is either coming past the rings or past the intake valve guide. An inspection with a bore scope in the hands of some one that knows what to look for would be a worth wile effort. A Broken ring can grove the cylinder and allow oil to be sucked up passed the rings. Watch for oil turning dark or black quicker than normal. Pay attention.
Dave

[Bruce Fenstermacher]

I agree with everything Dave said. If you have the equipment it doesn't hurt to take a look. But if a broken ring is tearing up the cylinder wall you won't have good compression. If a valve guide is worn excessively chances are the valve won't seal well and you more than likely you won't have good compression.

[Robert Eilers]

Thank you for the advice. My I.A. has a bore scope - we will atke a good look and go from there. I have a question about piston rings and ring gaps (for lack of a better description). I have heard that it is possible for the rings to swing around the piston during normal us and that sometimes the gaps in the snapped on rings line up just right and let oil past the piston. Is this fact or fiction?

[Bruce Fenstermacher]

Yes they do turn if all is well and yes the gaps can line up during this process.

[N170CT]

Dave,
Pardon my ignorance , but could you please expand on your comment about "Not the time to use auto gas"? I ain't figured that out yet.
Thanks,
chuck

[1SeventyZ]

I think what he's getting at is that auto fuel is already low octane compared to avgas, so reducing the octane by introducing oil is going to make your fuel charge that much more volatile and possibly pre-ignite.

[davevramp]

Octane is a figure of merit number that represents the stability of fuel with relation to temperature and pressure. 100 ll is more stable than 87 octane. When a cylinder is wet with oil some of it gets into the combustion process and reduces the stability of the fuel.
We all know of the stories of miss fueling were a jet fuel (oil) gets into a piston engines. If the cylinder starts lower on the octane ladder, Instability is closer than if 100ll were used.
On a cool day at low power settings things may be ok, but high temp, high power settings things could be different.

[GAHorn]

A cylinder "wet" with oil versus relative octane is a red-herring, in my opinion. The two have no relation to each other whatsoever.
The wet cylinder should be checked with a differential compression test. If the rings are leaking, then it's possible that the rings have simply aligned themselves such that oil is being allowed to slip past the rings, and it's likely that after a few hours the situation will right itself.
If the compression is low, and it's the result of valves, then it's possible that the valve-guide-to-valve-stem clearance is beyond specification and the oil in the rocker-cover is draining into the cylinder after shut down. (this is not a dire situation.... it's a relative situation, and the engine might actually operate safely and efficiently for many hours before repairs are necessary.... it depends upon the compression readings/interpretations.)
In other words... the sky is not necessarily falling.
Take the compression test. Follow conventional wisdom regarding the results. If a borescope shows evidence of cylinder wall scoring...then no need exists to continue the wonderment...pull the cylinder, repair the pistons/rings/cylinder, and go back together with it.
But if no damage is evident, and the compresseion readings are above 45 over 80 with no leakage past the exhaust valve.... I'd recommend running the engine another 25 hours and repeat the compression tests for another diagnostic evaluation.
It's most likely that valve stem/valve guide wear is alllowing some oil to settle into the cylinder after shutdown. Depending upon the severity of the wear versus the quantity of oil-fouling.... it may be worthwhile to continue operating another oil-change period before re-evaluation. I've seen several engines continue operation and this symptom disappear after a few hours. My 2 cents.

[N170CT]

Thanks gentlemen, I sincerely appreciate all the comments.
chuck

[Robert Eilers]

Completed the annual on 2767D today. The number #1 cylinder compression was 78/80. I will check the cylinder and the compression again in 100 hrs. Thanks for the advice.