I need to narrow a Bob Drake 41-48 ford gas tank. In order to get my exhaust to tuck in nicely, and come out exactly where I thought it was aesthetically best looking, I wound up with about 3/8 clearance between my exhaust pipes and the gas tank, which seems extremely close to me. So my best answer was to narrow the tank. Only thing is, the tank has previously had gas in it. I already laid out the cuts, and cut one of them (using a hack saw and air recip), so the tank is in half, and fumes are strong. This tank has sat empty for about 2 years now, and it still reeks. I know a lot of guys fill tanks with water prior to welding, however this one obviously wont hold water when its clamped together. Is there a chemical I can clean it out with (now that I have lots of room inside, I was surprised to find no baffles) for when I re-weld it? I will be TIG'ing it back together.
if its cut in two pieces..just toss a lit match at it and let it burn..it will not explode..its not contained .. When i cut my A tank up..all I did was run a hose from the exhaust off my Harley into the tank for about 20 minuets..than while it was pumping exhaust in to it i started cutting..the tank had been drained ,and was free from fuel for about 6 to 8 months when i did this..
Here is the official method endorsed by the US Army for welding fuel tanks: Run diesel exhaust thru it. It dries any remnants of gas plus there is no oxygen in the exhaust. I have done this many times, including using the exhaust from a gasoline engined car (but you do not want it to be running rich LOL). The exhaust from late model cars is fine, as long as the motor is warm so that the ECU is in closed loop. Water is often used but it is not fool proof. Exhaust gas is.
Check to make sure a 41 tank doesn't have baffles..........as a 40 does. Also when I tried to gas weld my 40 gas tank 30 years ago the metal kept developing small cracks right in front of the weld. I was told that the early tanks were made of a metal called Terne Plate and that it doesn't weld easily. Please let us know how yours turns out. Oh yes, I filled the tank with water while welding it. Finally fiberglassed the outside of the tank with fiberglass mat. No leaks yet.
When you clamp the two halves back together, hook up a hose running from the tailpipe of a running vehicle to the tank and weld it together. The exhaust fumes will remove all of the oxygen in the tank. No oxygen= no boom.
I have burped a few motorcycle tanks, and I still have all my fingers so??? I just wash it out with soap and water then wave the torch over the filler hole then work up the courage to put the flame in the tank. The worst thing that has ever happened is an 18" neutral flame burned for a second or two out of the filler hole. HOLY SHIT!!! Maybe thats not the best way, but it's the way I have dun it. haha
Filling with water can concentrate the fumes into any "air" pockets that might form inside the tank. I WATCHED a Honda CBX tank get turned inside out where the top tube passes when a guy used water and tried to weld it. Luckly the tank held together...or he would have been cut to ribbons.
I used detergent and lots of water when I did mine and it didn't blow. At least you're going to tig it, I tried it with a MIG, doesn't work, pin holes throughout the weld.
Thats why I planned on TIG, and plus, since going with TIG, I cant stand MIG welding, dont like the flying sparks!