Fouling spark plug - #2 cylinder - plug covered with oil

[john-ranger]

C-85 with 162hrs SMOH. My #2 cylinder, bottom spark plug is fouling out with oil on the plug. Compression on all the cylinders is 78/80. I found this out after doing a run-up and testing the mags. Any ideas what this could be and how I can fix it from happening. I'm a real newbie on this.

[marklamon]

C-85 with 162hrs SMOH. My #2 cylinder, bottom spark plug is fouling out with oil on the plug. Compression on all the cylinders is 78/80. I found this out after doing a run-up and testing the mags. Any ideas what this could be and how I can fix it from happening. I'm a real newbie on this.

My first guess would be a cracked oil ring. The oil ring is on the bottom of the piston. In most small "C" and "A" series engines the oil control ring is on the very bottom of the piston. During installation of the cyinder most people will leave the piston in the cylinder and slide the piston down just enough to slide the wrist pin out and put it on the rod. One of two thing happens next.
1. If the oil ring is on the bottom (lower) end of the piston it is allowed to expand and you must use a tool to compress the ring. Sometimes the ring does not get compressed enough and it gets broke/cracked while sliding it into the cylinder.

2. If the oil ring is above the wrist pin it still stands a chance of "peaking" out a little and getting cracked or broke during the installation.

I have pulled at least seven cylinders (different engines) that had good compression and poor oil control. Six of those seven had a cracked/broken ring. the seventh one had no expander ring under the oil ring.

The oil ring is not doing its job for what ever reason. After shutdown the oil runs to the bottom of the cylinder and puddles. During the next start the piston pushes all of that oil to the top and it gathers in the lower plug.

There is an outside chance that it could be the inake valve guide, but I doubt it.

I would run the engine until the oil consumption becomes to great. You can install a REM37BY in that lower hole. The electrodes on this plug extend further into the combustion chamber and tend to oil foul less. Mark

[john-ranger]

Cleaned the plug from #2. Re-installed. Fired it up. No problem. Mag. drop normal again (both sides). Shut the engine down. Started the engine half of dozen times. Let it sit for a while. No problem with #2. Was the oil on the plug an aberration? Should I be concerned about a broken oil ring or intake guide problem? I did not remove the plug to due a visual. Maybe I should. It runs fine however.

[Paul Agaliotis]

Just keep an eye on it. If you plan to go on a cross country take the parts and tools needed to replace the plug.

In my Tandem I always carry a spare plug (C26) and the tooling. Using non-shielded plugs limit your options when your not at home.

Paul

[marklamon]

Just keep an eye on it. If you plan to go on a cross country take the parts and tools needed to replace the plug.

In my Tandem I always carry a spare plug (C26) and the tooling. Using non-shielded plugs limit your options when your not at home.

Paul

Ditto,. Fly it.