well we can assume they where not installed like that because it would not have run right that way, so that happened while the plug was in the head. I would try a compression check and make sure that is ok, but with what happened is common at times when there is a failure for the piston to come up to far and slap the bottom of the plug.....however on that same note it may be possible that the wrong plugs where installed and are to long for the head to piston clearance, there is a few different things that could have happened. First have you milled/shaved your head or cylinders? if not then we can presume everything is stock? Then we need to make sure your plugs are correct for your motor? if they are then in best interest if it where me I would pull the head and check for damage, matter of fact as a pre look into pull the plug and look with a flashlight down into the hole inspecting the piston, look for a clean mark where it would have slapped the piston......tell us what you find
