Hi everyone, I’m doing the spark plugs on my ‘90 vert and the rear trailing plug hole is giving me trouble. I tried screwing in the spark plug but it wouldn’t seat all the way when screwing it by hand. It probably went in around 75% of the way. I installed the same plug into the other trailing hole and it gave me no issues. How do I know if there is an issue with my threading or if there is just gunk in the plug hole? I have tried pb blasting and drenching an old plug in brake clean and screwing it in, but no luck. If I try to screw it in with a wrench it seems like it’ll go but there’s resistance and I’m cautious to strip my threads if something else is wrong.

 

If I were in that situation, I would start with using my camera\endoscope and looking at the hole and threads.
My next steps would be based on what I see with that tool..