Author Topic: Fuel tank welding repair query ?  (Read 531 times)

Offline Stephen Foster

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Fuel tank welding repair query ?
« on: 03.10. 2022 15:31 »
Hello , Im in the process of restoring the fuel tank (Balloon type) on My 1939 BSA  WM20 ..the bottom edge all round is rottedaway so Im forming a new bottom and intend removing around 2-3" all around the rotten edge,butt welding new metal but am concerned about heat distortion around the top edge ? would Anyone have any suggestions for this please ? I am an experienced welder & have MIG , TIG or Oxy Acetylene but am undecided which to use ? Thank You in advance , Steve .
I own a 1955/56 B.S.A Swinging Arm "Golden Flash" , had it since 1976 .

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Re: Fuel tank welding repair query ?
« Reply #1 on: 03.10. 2022 20:29 »
I’m an inexperienced welder but TIG is usually best for thin sheet.

I’ve seen an experienced panel beater/tank guy remove a tank bottom using a coarse sanding disk on the (little) weld at the bottom of the sides, do the necessary repairs eg dent removal, then TIG the bottom back in. He rarely gets a leak, and has to go over the TIG weld again.
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Offline Stephen Foster

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Re: Fuel tank welding repair query ?
« Reply #2 on: 03.10. 2022 21:07 »
Thank You,

Ive done that ..removed and made a new bottom .

The bottom seam will be fine its the seam 2" higher up the tank wall Im concerned about .
I own a 1955/56 B.S.A Swinging Arm "Golden Flash" , had it since 1976 .

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Re: Fuel tank welding repair query ?
« Reply #3 on: 03.10. 2022 21:31 »
Quote
its the seam 2" higher up the tank wall Im concerned about .

So would I be - can't see how that could be done without distortion. I believe the trick is short bursts of MIG, though whether that ends up leak-proof is anyone's guess.....
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Offline Joolstacho

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Re: Fuel tank welding repair query ?
« Reply #4 on: 03.10. 2022 21:43 »
I'm no welding expert, but is it worth considering Brazing? obviously much lower temperatures are involved, -I've done plenty of repairs brazing, though obviously it's different to a complete reconstruction. Didn't they used to solder tanks back in the day?

Offline sean

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Re: Fuel tank welding repair query ?
« Reply #5 on: 03.10. 2022 22:50 »
Hello , Im in the process of restoring the fuel tank (Balloon type) on My 1939 BSA  WM20 ..the bottom edge all round is rottedaway so Im forming a new bottom and intend removing around 2-3" all around the rotten edge,butt welding new metal but am concerned about heat distortion around the top edge ? would Anyone have any suggestions for this please ? I am an experienced welder & have MIG , TIG or Oxy Acetylene but am undecided which to use ? Thank You in advance , Steve .

think I would put the cap on the tank fill the tank with ice cubes through the bottom then tig your patch in ....should keep the heat local ....when I weld thin body panels I tack weld opposite ends and eventually join the tack welds

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Re: Fuel tank welding repair query ?
« Reply #6 on: 04.10. 2022 07:45 »
I'm no welding expert, but is it worth considering Brazing? obviously much lower temperatures are involved, -I've done plenty of repairs brazing, though obviously it's different to a complete reconstruction. Didn't they used to solder tanks back in the day?
BSA stopped soldering tanks when they went from flat tanks to saddle tanks around 1920.
Most  soldered tanks had a bottom that was like a cup that the top of the tank sat in then the solder was run around the edges
The thick pin liniing hides the joint between the top & bottom,
Notrun used to scollop the upturned sides to get more surface area for the solder
Both joint faces were tinned then they were pressed together & oven baked to get the solder to join
If you look closely at the bottom os an unmolested BSA tank you will see the bottom is rolled over like a tin can lid
If they were tern plate then again oven baking will make a seal
Latter tanks with exposed ends were a rolling resistance weld
These tanks are the ones that rust out along the welds 
I am fairly sire that M20 tanks were braized edge on
This would have been a war time idea to save on steel
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Trevor

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Re: Fuel tank welding repair query ?
« Reply #7 on: 04.10. 2022 10:25 »
Taken quite a few bases off over the years for various reasons by grinding bottom weld, and then gas welded them back. But tank sides is a different kettle of fish.
Here's what I'd do (as I have done when repairing car doors / wings).
Form an overlap on existing edge (the tool required is called a joggler - bit like the tool used to set handsaw teeth). That stiffens and greatly reduces warping. The new metal then overlaps the old by around 1/2", with the overlap unseen inside. Spot weld the join and finish off with lead or filler. Lead would be best here from a leakage point of view. Personally, I've always found spot-welding (with a proper spot-welder) unreliable when joining old & new metal. It either doesn't bond or burns a hole, so here's my remedy: drill 1/4" holes in one side (in this case the new metal) at 1" intervals and use these to braze the join together (it's what they used to do to strengthen rally car bodyshells). Perhaps a little panel-beating then finish off with lead.
Good luck.
'49 B31, '49 M21, '53 DOT, '58 Flash, '62 Flash special, '00 Firestorm, Weslake sprint bike.

Offline Joolstacho

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Re: Fuel tank welding repair query ?
« Reply #8 on: 04.10. 2022 12:12 »
This is off to a slight tangent, hope nobody minds...
I've been fabricating a small brass part (steam cylinder) for an O gauge clockwork Robilt model loco. It's all pretty thin wall brass, and while it's pretty good, it's not perfect.
In the old days we used to use solder 'Tinman's solder' I think we called it, to flow and work like a filler. But what flux did we use?

Offline Stephen Foster

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Re: Fuel tank welding repair query ?
« Reply #9 on: 04.10. 2022 13:50 »
Taken quite a few bases off over the years for various reasons by grinding bottom weld, and then gas welded them back. But tank sides is a different kettle of fish.
Here's what I'd do (as I have done when repairing car doors / wings).
Form an overlap on existing edge (the tool required is called a joggler - bit like the tool used to set handsaw teeth). That stiffens and greatly reduces warping. The new metal then overlaps the old by around 1/2", with the overlap unseen inside. Spot weld the join and finish off with lead or filler. Lead would be best here from a leakage point of view. Personally, I've always found spot-welding (with a proper spot-welder) unreliable when joining old & new metal. It either doesn't bond or burns a hole, so here's my remedy: drill 1/4" holes in one side (in this case the new metal) at 1" intervals and use these to braze the join together (it's what they used to do to strengthen rally car bodyshells). Perhaps a little panel-beating then finish off with lead.
Good luck.

I had been considering using a joggler along the tank edge ..it would add stiffness I am sure .
I own a 1955/56 B.S.A Swinging Arm "Golden Flash" , had it since 1976 .

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Re: Fuel tank welding repair query ?
« Reply #10 on: 04.10. 2022 17:05 »
In reply to joolstacho, we use spirits of salts also called hydrochloric acid or muratic acid which is highly corrosive and needing thorough cleaning after soldering. Or, you could use a non corrosive resin flux if the item is easily tin able.
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Online Rex

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Re: Fuel tank welding repair query ?
« Reply #11 on: 04.10. 2022 17:27 »
I had been considering using a joggler along the tank edge ..it would add stiffness I am sure .

And a good joggler will have a reversible head and can be used to punch the 6mm holes too.

Offline Joolstacho

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Re: Fuel tank welding repair query ?
« Reply #12 on: 04.10. 2022 22:23 »
Ta Reg. And I wouldn't mind seeing some pics of this tank repair job.

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Re: Fuel tank welding repair query ?
« Reply #13 on: 04.10. 2022 23:10 »
But what flux did we use?
I seem to remember Baker's Fluid.

Seems it's still available!
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Offline Joolstacho

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Re: Fuel tank welding repair query ?
« Reply #14 on: 04.10. 2022 23:50 »
Been using Bakers for years - for soft soldering - wiring etc, but it doesn't seem to help for 'flowing' over a flat surface.