Rebuilding a Gas Tank

cfh

Well-Known Member
#1
I have a Gemini, which is pretty original except for the gas tank. It has some dumb wheezer tank, it looks crazy. So i got talking to this speedway guy (former member here, you may remember him), and he wanted some old shrike/scarab jackshafts/drivens that i have (on speedways i change them out to new comet series20 parts.) He offered to trade a Gemini gas tank for them. Seems Ok to me. He sent pictures, and i could tell it was a rusty... but when i got the tank, man it was a mess. it leaked around the bungs (it has two). I was able to TIG weld those, but after the tank held liquid for a while, it started to leak down the lower spine.

So i sand blasted the tank, including the inside. Man it got worse, a lot worse. So bad it was obvious i would have to rebuild the entire tank.

What follows is that tank rebuild. this was done with mostly normal tools. a TIG welder is needed at some point though. It's not an easy job, but it is do-able. I think a regular joe could probably do this if they have a welder and a hand (flap) grinder.

Tank after sand blasting. Looks ok, until you see the bottom...


Bottom of tank where the problem lies... It's swiss cheese...
 

cfh

Well-Known Member
#2
With some direction from friends, ground the original TIG welds on the bottom of the tank, until you see a 'line'. then stop! used a small chisel to get the entire bottom of the tank off. And then you can really see the problems! Holly crap this is a bigger problem than i thought. at least the inside of the tank is easy to sand blast now...

 

cfh

Well-Known Member
#3
Obviously need to make a new bottom. At direction of my friend, took some blue painters tape and put it over the old bottom of the tank. This will give us a mold to make a new bottom. Just remove the blue tape and stick it to a new piece of 1mm stainless steel, and can cut a new bottom.

 

cfh

Well-Known Member
#5
With the new bottom made, tack TIG welded the bottom to the tank. Did some repairs to the pin holes on the sides before welding the new bottom in place. Hard to get them all... but with some Pore15 tank sealer, I think this will be a fine gas tank. On the right side of the tank, there's a boop in the U bottom. Did not make that boop, but instead just tack welded the bottom in place. Then heated that area with a propane torch till it was red, and beat it into shape with a ball peen hammer. Not graceful, but it worked. Have to finish welding the bottom in place. But it's coming along. Took a few hours to do this, but overall wasn't too bad. Have to weld the tank mounts in place, but don't want to do that until i have the tank finished and i can see how it lines up on the frame.



Bottom line, this stuff is repairable. Maybe not really easy, but it's do-able....
 
#10
Obviously need to make a new bottom. At direction of my friend, took some blue painters tape and put it over the old bottom of the tank. This will give us a mold to make a new bottom. Just remove the blue tape and stick it to a new piece of 1mm stainless steel, and can cut a new bottom.

A handy tip when using tape to make a pattern like this is to drag the sticky side across your pants leg before you stick to the piece you want to copy. It will still stick but with much less grip. When you pull it off it wont stretch, tear or distort like it sometimes does when it is straight off the roll.
 
#15
Nice job I had to do that once. It made it easy to get the dents out too. I mig welded it and no sealer. It cloggs up the bung every few years but im too cheap to buy sealer lol.
 
#16
Wish I could see the images. I may be doing something like this myself. My tank is questionable at best. Haven’t tried to hold liquid yet. Doing a bunch of other cutting and grinding to prep the frame.
 

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