Hey everyone. Helping a friend with his 78 cb750 k and as we were doing the spring tune up he turns to me and says this one spark plug is going in funny? I said did you start to put them in by hand assuring they went in smooth. He says yes. Upon investigation it appears that a little down the plug hole it appears to cross threaded. The plug goes in over half way before it becomes affected by this. He said it felt like it came out smooth like the other 3 and the all 4 old plugs appear to have the usual wear you'd find. So my question is what's the next step? The motor runs nice and the bike is great. We haven't done anything to it since discovering it yesterday. Any help would be great. I was thinking a tap and die but did not even try that yet. I figured il let you guys the experts chime in. Thanks guys in advance