TIG Brazing Steel/Alloy Rolled Lip Fuel Tank

[eSCHEn]

I've got a small fuel tank (~1L) with a leak from an otherwise spot on Briggs and Stratton 35 classic engine. As you can see from the pictures it's had a bash from something and that has deformed the rolled lip seal. Someone has had a go at sealing it with some epoxy putty and it's not worked.

I've brazed with OA before and I'm confident soldering and can do a little bit of leading but I've never brazed with TIG before. I see there's a few formulations of rod, which would be suggested for the tank here? Bottom is mild steel and top is alloy of some description.

Other than the very obvious safety issues are there any caveats to be aware of? Is there likely to be a sealer in that seam?

I'm intending to just run a bead round the whole perimeter of the fold as that's the only place that it's leaking from.

 

[gordon stephenson]

I think that I would be inclined to solder rather than braze.

 

[Richard.]

@hotrodder builds and repairs stuff like this all the time.
My initial thoughts would say not to tig braze it but OA if possible.
Ive done bits with both and OA tends to flow better and be more forgiving. As with any brazing the heat needs to be controlled this is quite difficult with tig as its very localised even with an increase in arc length. My tig brazing has mainly been done on brass components where my preferred method is on AC with aluminium bronze and a foot control. Ive also done a few aluminium castings with 4047 which is actually very close to welding due to the melting point of the filler been close to parent. I'm waffling on now but in reality I think there may be better results on your job with silver solder or Gas braze.

 

[eSCHEn]

Gentlemen thank you. I'd been mulling the same idea of whether solder would be more forgiving in the long run with vibrations.

My next heat option under the TIG is a propane torch so I'd be thinking of something along those lines. Would plain old plumbing lead work with a plumbing flux? If not then what would you choose, silver solder?

 

[xmetal]

I think I would use silver solder as it's stronger than the normal 60/40 tin lead solder.

 

[eSCHEn]

I've never silver soldered before so this will be an experience I'm sure

Was going to ask about it but this seem like a good resource: http://www.pollymodelengineering.co.uk/global/technical-notes/basic-silver-soldering.asp

 

[eSCHEn]

Okay I've seen the prices of rods and flux and now want a wee lie down

 

[xmetal]

Silver solder melts at a higher temperature than 60/40 but still way below brazing. I think you have just found out it's dearer too!

 

[Richard.]

Okay I've seen the prices of rods and flux and now want a wee lie down

Again D it's worth getting Hr's take on it before going further simply because he's also very resource full with where is best to get your filler and flux.
You will probably find he knows an alternative that's the same for less cost. Worth an ask.

 

[Chris Stevens]

Silver solder is the best option, but if you are wanting a budget job soft solder would work fine. Many old bike tanks were made using soft solder........................

 

[The_Yellow_Ardvark]

Not sure if this is correct.
But is was past to me by a old time Motor cycle engineer. (sadly no longer with us, so I can not ask him for for more information.
He was fixing bikes up to his late 80'

But I am sure we will get an answer.

He would OA a tank using soft or silver solder. He claimed the following.
The joint would be a bit flexible.
The oxygen in the flame would help burn of any red oxide in the joint. This is the bit I am not sure on.


In the past I have used OA to burn of rust, scale and crud in hard to reach areas prior to MIG'ing a rust bucket of a car.


I have soldered up a few tanks in the past with OA, not had an issues.

 

[Chris Stevens]

Just had a close look at OP post, and as the tank is MS with crimped joint to aluminium top, I would guess silver solder isnt going to work. Think blast cleaning and Devcon is a better option...................

 

[eSCHEn]

OA would have once been my first choice but a) it's horrifically expensive and b) I don't have it and c) I think I'm genuinely a better TIG welder than gas now (not hard lol).

Will see what mr rodder says if he's got the time and sees this. Can't progress with Elliot Shaker (in honour of Pete.) until I find a trolley. And yes, I do know they sell them for a pound

 

[xmetal]

Just had a close look at OP post, and as the tank is MS with crimped joint to aluminium top, I would guess silver solder isnt going to work. Think blast cleaning and Devcon is a better option...................

You're right, I didn't notice it was aluminium.

 

[Screwdriver]

Either way, I'd be tempted to pull out the crease first. Either with a slide hammer or panel beat it. The proximity of a nice big hole means you could easily fit a dolly in there.

S.

 

[Chris Stevens]

Anyone who can join steel and aluminium inexpensively using TIG or OA is a true expert....................

 

[The_Yellow_Ardvark]

I was one who didn't notice it was a mix of ally and steel.
guilty as charge M lord.

How about after removing the dent using one of those 2 pack tank sealant you slosh around the inside?

I never used them myself, might be worth a shot.

 

[xmetal]

I've used some special solder for use with aluminium but it was never very successful. You need three hands, one to hold the torch or iron, one to add the solder and one to scrape the aluminium to get the oxide off in the melted pool. It would tin intermittently so it was a hit and miss affair.

 

[Screwdriver]

Surely a decent propane torch would be a better option for thinner material like this? You could even braze it or use one of those trick low temperature alloy filler rods.

 

[hotrodder]

If it's an aluminium or monkey metal top with a pressed steel bottom then i'd forget about fixing it by soldering or brazing or welding. The zinc based self fluxing solders that shills hype up don't work on steel and while they or some other "special" solders may work if the steel side is galvanised and spotlessly clean there'll probably be a long list of caveats just like there is with posh processes like Fronius CMT when it comes to "welding" aluminium to steel...

Even if the monkey metal or some other solders would work they'd be the last thing i'd think about using these days. Especially for something like a lawnmower or whatever that isn't used daily due to the properties of 'modern' petrol. Zinc and tin/lead terne coatings/solders are somewhere near the top of a long list of materials that don't like ethanol blends of petrol

Not practical to repair a crimped joint (or easy to do) but FWIW aluminium can be brazed (with 4047 and the appropriate flux) to steel if the steel side is first tinned with silver solder

Assuming replacements aren't cheap and/or easy to find i'd make a new one. Either from scratch or using part of the origional say by salvaging part of the ally top (assuming it is aluminium), making a new bottom out of ally and welding the two together