I agree, probably could have used more heat. I could not get it cherry red. I don't know if that's really possible with alum, is it? Did all I could do with my little torch which generally works well on steel.
For welding I have a pretty decent wire feed. Guess it's worth a shot, but not feeling lucky today. How do you keep the nut in place while filling it up with weld?
I did not use a helicoil for the repair, got a solid sleeve insert. Not wanting to spend big bucks on a $60 motor, I bought a cheap kit which I think may have had mismatched tap and insert threads. With no spring or tang, I installed the sleeve with Locktite and used Never Seize on the plug. Figured once it set up just the plug would come out. Nope, plug came out with insert turning into a spring anyway, and pulled even more alum out of the head. How does that even happen? It's like the alum is brittle or something. I tried to reinsert the whole mess and it never got really tight. Motor actually started and ran, but I knew that plug would just blow out eventually.
Think before I try removing the power head I'm going to bolt it together with only 9 bolts. If I do have to remove it, I see more busted bolts in my future. They've just been in there too damned long.