I did what you suggested only I used everyday penetrating oil. In the process, I learned a lot about heat risers. For one thing, the counterweight is not just pressed on, but has a 1/8" pin through it, but if you hit it hard enough, it-will-break. No sweat there. I finally got the entire valve out, and cleaned up the rod and it turns freely now. Part of the end where the spring goes was broken off, so I turned the rod 90 degrees and sawed another slot in it. Now all I have to do is get a new spring, set the thing up, and re-weld the valve plate to the rod. Thanks for your reply!