Pop back through the intake?? leaking or bent intake valve or exhaust cam lobe gone. Your timing gear may have gone to lunch, and jumped out of time.The piston struck an intake valve bending the head.The exhaust valves on Stovebolts are recessed, no interference posssible, but the intakes are almost flush with the head face.The fiber cam gear with a metal insert is keyed to the cam shaft.Perhaps the fiber is weakened with age and has slipped on the insert.Or the slip in cam timing may be enough to cause popping without valve train damage.The bent intake push rod is the clue to the mystery.
One the other hand I think the engine wouldn't run at all if the timing jumped due to a broken tooth.. What happens when the missing tooth comes around again while the engine is running?Maybe the variance in the cam timing you noted is just worn parts.Does 40 thou affect the timing enough to make a low power engine like a 216 run lousy?Gotta pull the pan to get off the timing cover.Do you have access to one of those mini cameras to have a look into the spark plug hole?
