This is a follow up thread from another I started last spring when I had a prop strike, the engine was torn down and inspected as per the FAA regs but never ran right when I got it back ( the aircraft is only 8 years old and the engine had 275 SNEW when the incident occurred) . I've spent the last 9 months taking it back to the engine shop trying to zero in on the problem after many misdiagnoses and unneeded fixes and tweaks that didn't solve the main issue. Specifically the bottom plug on cylinder number 1 kept gunking up at low rpm, running a fine wire (hotter burning) plug would fix the rough running I assume by burning up the oil that was fouling it when testing the mag that was related to that bottom plug, but if I put the regular plug back in it would foul up again when taxiing or operating at low rpm. It was agreed with the insurance and engine shop that a brand new cylinder/piston/ring kit would be installed which they are doing now. Prior to starting the job on Thursday the mechanic told me the problem was caused by "ring chatter"' which he describes as the join part of the ring not being seated correctly allowing oil past and through onto the plug which gets fouled up then causes a misfire unless it is cleared with excessive leaning during run up. The reason I asked the question is this isn't the first time I've been given a new explanation for the problem then after the recommended fix the issue resurfaces, I want to better understanding what he is telling me about this "ring chatter" which worryingly is at odds with what BPF describes and the compression checks come back within tolerance which also leads me to doubt the mechanics opinion.
Edit to add: ATC I had the timing verified by a second shop so I know that's not the issue.