Do you use anti seize on your spark plug?
If you have damaged the threads you can not "re tap" to the same size.
You could try a heli coil repair... I have not ever liked that process... a far better system is "time sert"
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I have put many time sert repairs in my friends ford engines... after they had 'plug blow outs'...
If your threads are stripped, on a small engine, you may be better just replacing the head...
Take the plug out and examine the threads. They will Not get better forcing them... KennyV