The Cessna 120-140 Association Forum

I’ve been having issues with black sooty exhaust from #2&#4 cylinders. Traced it to #2,top of piston wet and burnt oil in cylinder. We did a borescope and cross hatching is good. Question is can it be a stuck or cracked oil ring. We’ve flushed it out with Mike Busch method using Xylene,mineral spirits and Shell 100 oil recipe. Any answers?

How is the intake valve guide?

Can you get your borescope in a position to see the valves when they are open?
You need to look at the stems and seats.
It not easy but can be done.

Rick

Finally found issue- two stuck rings. Carbon.