puzzler for ya

If you cant see anything down the plug hole......put a plug in it and turn it over manually....remove the plug. If the plug is closed again......there is ONLY ONE thing in that cylinder that CAN hit the plug and that is the piston....Unless of course some idiot dropped a washer down the intake( unlikely) good chance your pistons are matched but that is a possibility as is the connecting rod. If the CR is just a TAD longer than the rest or if your heads were decked....you might have found your problem.
Either way it will likely NOT be a simple fix....not trying to freak you out...just trying to sanity check the options......Chance favors the prepared mind.....you may be lookin at a partial rebuild