Help with the #8 plug

[PNYXPS66]

Actually, I had the #4 plug on my '66 289 do the same thing. If the suggestion with the brake cleeaner and 50ft/lb torque (geez!) doesn't work, I'd suggest a more radical, yet permanent, approach -- remove the head and have a machine shop drill out the old threads that are stretched and insert a heli-coil threaded replacement insert. It's permanently installed and won't give you another problem. My concern with the torqued approach is that if the threads are already stressed out, they may not take 50ft/lb torque and the plug will strip in the head. Then the only thing torqued at that point will be you because you may or may not be able to remove the plug. I usually tighten plugs snug then an additional 1/4 turn. The heat of the engine will make the plug get tighter as the metal expands and contracts. Good luck.

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Pony Express 66
God Speed and keep it between the lines!