Not only was the tank mangled, but once I sawed it open, I found that it was severely corroded and contaminated inside.
First I beat out all the dents, then I got the rust out. First I cleaned it with a wire brush in my hand grinder, then I got it to bare steel with acid. Once all signs of rust were gone, I washed it with baking soda to stop any more acid action. By then it closely resembled a screen door with all the rust pits completely through it.
I coated the inside with JB weld to seal it up.
I made a ring of metal from a door panel off of a Camero, then slipped it inside for backing, then tack welded it in place.
The fellow at the body shop who gave me the door panel told me I should tell everyone it was a Camero outboard. I told him that the guys who'd care would see through that in a heartbeat, but I might say I used some Camero parts to restore it and suggest they try to figure out which parts they were. Since they are completely inside the tank, nobody would ever find them. I've let that out of the bag now, though, so I don't guess that gag would fly!
Now I don't have to weld an air gap up, I have something to weld to while filling the void left by the saw.
And here's a close up of the ring of metal.
This is the semi-finished product. I've welded it, ground down the welds, and soon it will have a coat of filler to smooth out all my rough work.
One of the hard parts was to weld the bottom back in, doing the welding 1/4" to 1/2" from that seam around the edge. That seam is soldered, so the weld temps would easily melt all the solder out of the seams and make it leak.
The way I solved that was to weld in short (1/2" or less) welds, putting a very wet towel against the side of the tank. It didn't take long for the towel to start steaming, but by working slowly, and keeping the towel very wet (water boils at around 212 degrees, solder melts at maybe 450 degrees) I was able to weld it all back up.
I have something called a "sloshing compound" that I plan to use to make sure the tank is sealed up well, and hopefully to prevent any more rust from developing. It is supposed to leave a coating all over the inside of the tank.
Was it worth it? Who knows. I probably have 20 hours in this tank, but you can't go out an buy one. I probably accomplished more than if I'd sat in from of the idiot tube watching worthless sitcoms. It's probably the only way I could get this nice Firestone motor back in shape, since I can't run down the street and buy a new tank.