Back in January while taking a nice 200 mile day trip, the motor starting missing badly.

I was a bit overdue for a valve adjustment, so I adjusted the valves and when I pulled the plugs discovered that the electrode on Cyl#2 was bend and touching the center post. Thinking that it was from a drop, and that it (and all the plugs) looked great, I re bent it and replaced. All was well for 100 miles till it happened again. Same plug same issue, definitely a light piston strike.

Thinking carbon build up, I tried to decarbon the cyl, but it happened again when the engine was fully hot (cyl head 325, oil 200-205). I bought a cell phone borescope to check the cyl and found the following. Hard to tell from the pic, but it looks like the oil is coming from the top and running down the cyl. May be broken oil ring, but not sure. The streaks are oil lines not scuffing.

Click to view attachment


I have some index shims coming as a temporary fix, but figured I'd run it past the brain trust. Plan to check compression to see what is going on too. Should be done hot correct? Haven't done one in 20+ years.

Motor is a 2056 modeled after the early Raby build, has the KB pistons, Hoffman rebuilt heads, Dellorto 36's, Pertronix ignition, about 20K on the build, and this is the first problem. Installed Tangerine Cooling system in the fall, maybe 500 miles on it.

Other than this, the motor has run flawlessly, and this is the first issue other than the alt bracket issue which is solved.

I'm thinking of dropping the motor and doing a professionally built short block 2056, swap everything over then take my time to dig into this one.

Appreciate any insight or leads on a decent 2056 short block.

My 2L standard spark plugs, forget now the exact model socketed too deep in the head.
Pull your plugs and look for carbon on the last couple threads, could need slightly shorter plugs. funny it's only happened to 1 plug, are they all the same ?

Yes, all the same, and no changes to the engine internals for 5+ years and 20K miles. Very odd and frustrating. I did a test of the plugs before assembly to see how they would end up in the head and no issues with being too deep, seemed perfect.

I think it is carbon, from the oil in the cyl. I hate the idea of a shortcut fix, but...... it is what it is.