The other plugs look fine?

I would work on the premise that there is an object in the cylinder. My favorite machinist has a little periscope he can put in places like that to look around, maybe you can borrow one.

Oh and in case you are feeling like a knuckle head I once dropped a 3" stud into a cylinder and forgot it was there and so when i cranked the engine over it fell in there and then pushed a hole in my piston. Ouch! That cost me about 2k to fix. I had to buy a piston and all new bearings plus have the block stripped and cleaned IIRC.

Just don't run it this way and you wont spread debris into your bearings. (like I did).

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.