Welding a fuel tank lock ring.

R

rjlester

Senior Member
Hey Guys,

Last week I installed a new fuel sending unit in the tank of my 57 Monarch, and while I turned the lock ring, one of the three welds broke on the tank. The tank has it's own lock ring that the other ring twists into, so I only had 2 out of 3 tabs holding. I had to take the car on a road trip last weekend, so I left it as is and it didn't leak the first day.

Day two it leaked so now I want to remove the tank and weld that ring back on. What's the best way to do this? Empty the tank, then fill it with water and weld away? I'll likely just give it a few quick stabs with the mig welder, but don't want a fire obviously.

The car was flawless on a 1200 mile plus trip, never opened a toolbox. The old 312 has me really impressed!
 
I just read online about using exhaust gas to fill the tank with inert gas. Seems like a good idea after it's been rinsed out. Thoughts?
 
I have been very successful rinsing with laquer thinner, venting with a hair dryer for a couple of hours. Never had one go boom or started a fire doing it this way.
 
Alright, I can confirm the Lacquer thinner trick worked. This is what I did, all outside:

After I drained all of the fuel, I added about two cups of the lacquer thinner in there and sloshed it all around. Dumped out what I could once I finished shaking it all around.

Then I ran the garden hose into it and went in the house for lunch. By the time I came back it had been overflowing for about 15 minutes and it had a good flush. I shook this water all around to make sure all air pockets were sloshed.

Drained the water. Then I put the tank out in the hot sun, and ran the shop vac blowing into the tank for about an hour. A few times I switched the location of the blower hose to either the filler neck or the fuel sending unit hole.

After the hour of blowing air into it, you could not smell gas or the lacquer thinner coming out any more. Wearing ear and eye protection, I waved a propane torch over the hole, and when nothing happened I put it right inside the tank. No BOOM at all!!

I proceeded to weld the locking ring onto the tank, every 3/4 of an inch or so. I created a couple of holes so I plugged them with gas tank repair putty. After an hour letting that harden, I put about 7psi in the tank, and checked for bubbles. Fixed one small leak I missed the first time, and then installed the tank in the car. We will see the next time I fill it up, but I suspect the lock ring will stay in place now.

Hope this method helps someone else feel safe welding their tank.
 
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