70 tossed out its spark plug.
 

Tonight I was mowing with my old 70 for a hour or so and it ran great as always. I was minutes away from being done when it lost power labored and then bang! It spit the spark plug out of the head. The plug was tight and the head threads came out with the plug. I have never seen that happen before. Any ideas as to what happened? Was I working it too hard? Or maybe the threads were stressed from old age? Fortunately I have another head I can swap out but I sure would like to know what happened.

Previous spark plug installations could have been out of spec ( too tight or too loose ) and the aluminum finally failed.

If the head is still good, a helicoil can save the head and it can last another few decades.

I was thinking about trying to helicoil it. Maybe I could get a few years out of it.

Make sure it's perpendicular and you don't wobble at ALL when tapping. Otherwise the threads will end up oversize.

Do you have a drill press? It would be best to bolt the head down to keep everything straight and on center.

If there is interest in offering installing helicoils in heads, I'll buy the kit to do it and add it to the services offered.