Something In my #5 Cylinder?

yellow rose said
I'm saying something got in there and it was getting smacked around. You have zero clearance when something is getting smashed between the piston and the head. And the Rod bearing takes all that load.

It doesn't take long beating on a bearing like that before it develops some extra clearance. Not enough to make noise, but enough to let the piston punch the spark plug right in the mouth!

Thanks for the clarification. Now I understand what you are trying to say. There was something loose in the cylinder first, which damaged the top of the piston and the rod bearing, then the damaged rod bearing allowed the piston to contact the spark plug, which closed the plug gap.