Hi Scotty,
I have one cylinder that has white barnacle like build up on the bottom threads of the spark plug chamber, in one cylinder that is preventing the new spark plug from seating. The old plug came out clean, but the carbon or sludge? is preventing the new plug from being inserted all the way, stops at the sludge. I do not want to knock anything into the head that would be harmful. Is there anything that will safely dissolve the build up?
Well that's weird that the old one came out but what you could do is spray any good carbon cleaner like GDI spray carbon cleaner. Let's hook overnight then crank the engine over with the spark plug. Not in the hole and if any crud has been removed it will just blow it right out of the cylinder hole when you crank the engine over without the spark plug in
