Spark plug threads question... I know wrong forum

[Rev. Scott]

Got a base line compression check on my "new-to-me" Thing. 1 2 4 are all in the 125 to 135 range. 3 came out with knackered threads blow-by and what might have been a failed heli-coil. How screwed am I? Outside of JB Weld...can I fix this in place? Or just suck it up and replace the heads. Couldn't thread a new plug in but the old one found its way "home". I trust my friends here first...fire away. Thanks.
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"I haven't seen one of those since I was shootin' at 'em!"

[Wildthings]

A Timesert or other insert with a larger OD might get you going. Are your heads 1/2" or 3/4" reach? Not uncommon to find 3/4" reach heads with 1/2" reach plugs installed, in which case you can chase the threads and go to the correct longer plugs.

[mondshine]

I agree with Wild.
But the engine should come out regardless. The Timesert (or Bigsert) is a good repair, but your chance of success is much better if you can see what you are doing with the engine out, and cylinder cover off (especially for one of the "forward" cylinders).
Besides, since this Thing is new to you, it's a good opportunity to have a look around.
Good luck, Mondshine

[Rev. Scott]

Thanks. (Just noticed how jenky my keyboard was/is in the subject line.) This is a mystery dual port in my '72 military. Always been gutless...guess I have some idea why now. All the plugs looked acceptable...but you could see where #3 had been blowing past the "threads". If I'm yanking the motor...it's time to do it right. First good storm is moving in today...will update. Damn I hoped there was a scabby quick-fix.
_________________
"I haven't seen one of those since I was shootin' at 'em!"