Tap plug on end that free up threads I'd heat coupling with propane torch first. They never needed full 1/4 inch pipe torque to begin with to stay in 15 ft. pounds hold them for ever. When got my plug out I weld large washer on end plug so have pull ring to pull trellis wire tight. I have 1973 & 1977 its 4 speed both have new engines overhead valves they pull harder than flat heads.

Are you talking about the plunger and spring that hold the depth bar in place?

Yes baymee, the little tube with a spring inside to keep the depth bar in the notch.... can;t break the plug loose to replace the spring for better tension on the bar.

Heat with a torch. Use penetrating oil. Tap with a hammer. That's about all you can do.

mrt: Further to Bay's advice heating the tube and then quenching the Plug with cold water then quickly attempting removal of the plug sometimes also is beneficial in stubborn cases where heat and penetrating oil alone has not sufficed.

Thanks guys... I'll try those ideas maybe tomorrow... only thing is, I've been putting penetrating oil on it for about a week now and still not a budge; hopefully the heat and tapping will help... I'll let you know.

When you do get the plug out,and before re-installing put some anti seize compound on the threads. Sure makes it easier the next time the plug has to be removed. Not sure how old my Horse is but, it has the original cast iron Clinton engine on it. Got it at a yard sale about four years ago for $100. Had been stored in a barn for at least twelve years.

Heating it red hot and letting it cool will probably help. Just don't use any tools on it until it cools to a gray color.

mrt: I would be surprised if the Heating and Quenching does not resolve the seized condition. When you expand the internal threads of the tubing via the Torch Heat (Red Hot) then quench the Plug the external threads of the plug will shrink slightly and the Galled condition will be eliminated for a few seconds. Just enough to quickly remove the Plug. Follow Nods advice on the anti seize compound sure makes life easier next time lol .

I just re-read your post. You want to remove a frozen bolt? I have to look at mine and see what you're talking about.

Using a torch, penetrating oil, and an impact gun should fix it.

Put the impact gun to it's lowest setting and let it rattle the bolt. Increase the pressure gradually. Before doing all this, heat the bolt to red hot and quench it.