welding on gas tanks

[monty101]

anybody ever moved the spigot from the middle of a fat bob tank to the rear. Looks to me that if I did that I'd make my tank hold about a gallon and half more. Just never welded on a tank that had gas in it before. I guess I could fill it up with water and get my old lady to stick a torch in the filler hole??

[76shuvlinoff]

  I've heard of guys filling them with water, never tried it myself. When I was a kid I watched my old man solder up a car tank by running a hose from an exhaust pipe into it until it was dryed out then he rinsed it out with soapy water.

[Evo1]

It's the fumes that are explosive and water displaces air so it should in theory displace the fumes.....who wants to go first?

[06ultra]

I've weilded a couple mc gas tank leaks before, I just flushed them out real good with soapy water and blow air into the tank then let it sit out in the sun to dry and you're good to go,

[hardtail84]

What Ultra said, done it many times.

[d-dog]

I've done a few too.  After all the rinsing and drying, I still run the auto exhaust thru it while welding.
Dog

[buzzurd]

Done several myself and it's still a bit freaky.I rinse it out several time and then run a slight amount of compressed air into the tank while doing the welding.Remember years ago welding a gas tank in a old Rambler (car) I had.Rinsed several times and decided to be safe and throw a match at it from a distance.It shot out a flame probably 6 feet long and sounded like a rocket.After that it was good to go.By all means BE CAREFUL!!!!!!!!!!!!
Buzzurd

[Tow-Truck]

I had a tank blow up that had been washed out and filled with water. I only weld them now if they are full of exhaust fumes. Purge the tank first with a co2 extinguisher

[MMOCGuy]

I've welded motorcycle gas tanks many times. My process is that I fill them with warm, soapy water and let the water run out the top (Over flow) for a minute or so. I then empty the tank and repeat it one more time. Since gas and gas fumes are lighter than water, they rise to the opening as the tank fills and then, as the tank overflows, the excess water washes both fumes and any residual gasoline away. Usually the first cycle does it but I do it a second time just to be sure. The third time I fill it just until it starts to overflow. Then, with the tank full of water, I stand back a toss a match at the opening just to make sure all of the fumes are gone  (I've never had so much as a burp). After that, I empty the tank and weld as much as necessary. The heat from welding will usually dry out the tank.

Hope this helps.

Norm.

[Harpo]

What Norm said.  Fill with water and let it 'boil' out the top for awhile.  Let it dry and then toss a lit match in the opening.  Nothing usually happens but every now and then you'll get a FOOMPH (did I spell that right?).

[Hillside Motorcycle]

You spelled it right.
We've welded a lot of them over the years.
Be careful, and you'll be just fine.

[monty101]

I'm going to do it tomorrow. All I have is a stick welder and some 6011 rods. Anybody got any input as to what the chances are that I can weld it up and it not have pin holes. I've used that welder to stretch the frame and it does pop a little. I have to put some pipe nipples in the rear end of each fat bob on one set so the gas from the right side can get over to the other side. I'm going to put some regular threads on the pipe and run a nut onto it put two holes in each end of the tank and thread it to fit the pipe and screw the two pipes in and run the jam nut up against the tank. then use my stick welder I intend to I hope weld the nuts to the tanks to eliminate the possibility of them coming out and also leaking. I have to do the same thing to the other two fat bobs plus move the spigot hole back from the middle to the rear of the tanks. I figured I'd use a 4 inch cutoff grinder to cut out a square around the spigot and then cut a smaller hole at the rear and set the spigot in it and weld it in. Then I'll get a square piece of sheet metal and cover the middle hole and weld it in. Ques is can that be done with a stick welder or do I need to get some one to mig weld it??

[Showdog75]

I think you should have a competent welder Tig weld it .  I purge with argon , much better weld on the backside . Unless you are a very good welder I'd forget about stick welding it . It can be done but you better know what your doing . Btw this is what I do for a living . Let us know how it turns out . Pics would be nice .

[Showdog75]

Let me say one more thing , DON'T STICK WELD IT . Trust me . Mig would be better Tig would be the best .

[Ultrashovel]

Let me say one more thing , DON'T STICK WELD IT . Trust me . Mig would be better Tig would be the best .

I have to agree. Stick is fine for some things like new, thicker metal. With sheet metal, you have to have a lot of practice and go really fast.

As Mr. Showdog says, Mig or Tig would be better. There would be much less chance of incursions and pinholes.

[monty101]

I'll get it tig welded, thks for the advice. If I had the right attachments I could braze it but I can't find them.......

[Old Crow]

I certainly wouldn't braze it. 
I had a friend who tried to braze up some rust holes in a 5 gal jerry can that was used as a water can.  The can had never had gas in it since new. 
It apparently filled with acetelene mixture while he was welding on it.  When it blew, it came apart at the seams, the bottom(he had it upside down welding on the bottom)flew straight up in the air(BTW, taking one of his "boys" with it)and the rest of the can split down the side seam, flew about 35 or 40 feet and took out his bedroom window.

[pappyfreebird]

well i run fum em anymo...me n my pappy (he) were gonna weld up my 10 jeep tank many moons ago...filled n rinsed etc sun baked etc...he evin stuck torch in filler befo we started ,,nuttin,, so i hold her on this five gallon bucket n pops hits it wid the torch n begins ta braze n fuggan voof boomie ca-plowie,,i were on me back watchun this fuggan tank fly threw the air landin in neighbas yard (opind up like a fuggan sardine can,,1st good look at a in tank baffel!!!) meantime torch flew in garage n set a small fire n me pappy was holdin his hand funny as i stomped out the fire n grabbed torch,,,the ol boy broke two fingers...so after havin his fingers set he orderd me a bran new one outta jc whitney..i member him sayun well i sure az L blew that one...wed aways yeup ain that the truth...so ive aways had a slight fear when comes ta tanks

[Ultrashovel]

well i run fum em anymo...me n my pappy (he) were gonna weld up my 10 jeep tank many moons ago...filled n rinsed etc sun baked etc...he evin stuck torch in filler befo we started ,,nuttin,, so i hold her on this five gallon bucket n pops hits it wid the torch n begins ta braze n fuggan voof boomie ca-plowie,,i were on me back watchun this fuggan tank fly threw the air landin in neighbas yard (opind up like a fuggan sardine can,,1st good look at a in tank baffel!!!) meantime torch flew in garage n set a small fire n me pappy was holdin his hand funny as i stomped out the fire n grabbed torch,,,the ol boy broke two fingers...so after havin his fingers set he orderd me a bran new one outta jc whitney..i member him sayun well i sure az L blew that one...wed aways yeup ain that the truth...so ive aways had a slight fear when comes ta tanks

Good point, Pappy. I took a Matchless Motorcycle fuel tank to a welder I knew years and years ago to have a crack fixed. He filled it with water after purging it with the exhaust pipe on his car for a half hour. (Gas was cheap then.)

He set it on a stand and started to heat the metal on the crack and, WHOOSH! A bolt of flame came out of the tank that was ten feet long headed straight up. It sounded like a .45 going off. After that, he welded it OK but I bet he had to clean his shorts after a while.

The thing about welding gas tanks is you can do ten of them in a row with no problems and the last one will blow and there's just no telling when. It just has to be the right combination.

I've welded a few in my day but I never forgot that day with the Matchless.

[monty101]

well I got one finished sort of. I just added aftermarket extensions to some softail fat bobs.
they have the spigot already back in the back. Still trying to figure out if I am going to put crossover plumbing in the rear end. These hadn't had gas in them for several years and they were no problem. the other tanks have gas in them right now. They are going to be the problem if I have one.

[76shuvlinoff]

 I'm a bit chickensh*t. 
Sept. 3rd 1971 ( just going into 6th grade and on my Dad's birthday no less) Dad had his back turned and I thought I'd toss a soup can of gasoline onto a rubbish fire.  I spent exactly six weeks in the hospital, 3 before the skin grafts on my legs and 3 afterwards. Put my folks thru hell.  Much later the old man said it was one hell of a stunt to avoid going back to school the next day.   I don't screw with gasoline much anymore.

  Mark

[pappyfreebird]

i hear that sns...ceptin my dumb bs were wid blackpowder..i blew a hole n landid in it..my momma aways said i r livun proof theres a God...but then again i rekon i were prolly 13 befoe i realized my real name werent dayum kid!

[monty101]

oh, crap, double crap, I burned a hole in the tank with my stick welder and I welded up the hole I thougnt but just as you guys said I can't get rid of the pin holes. guess I'll have to find a tig welder now.

[pappyfreebird]

better yet buy one a these fum ol paps here

[attachment removed after 60 days by system]

[monty101]

Well found a welder that can braze up all my screws ups for 50 bucks. I decided to put transfer tubing at the rear of each tank so I'll get all the 5 gallons out of the tank. I put some extensions on it that resulted in me having to tack weld and that guaranteed there'd be some holes punched in the tanks because all I have is a stick welder. The extensions looked like crap because they curve out at that back so I got my 4 inch cutter out and sliced off enough in the right places to get rid of the curves. Now they are 22 inches long and straight with now curves other than a slight curve on the bottom edge that the extensions create. I wanted some that look like regency 6 gallons but don't cost $295. I've had these tanks for many a year and didn't realize they were 5 gallons until I laid one down by a 4.2 gallon. I cut the front transfer tubing connections off some beat up 4.2 gallon tanks to put on the rear of these tanks. Should be good for 43 x 5 = 215 highway miles and 25 x 5= 125 in town miles. They'll be a big improvement over those ugly a-- Jerih 6 gallon tanks. Plus they are original and I guarantee nobody else is running them. They always caused a commotion anyway because they had what some people thought were death heads on them.