Fabricating a petrol tank

[Kafer_meister]

I've got an early SWB Shogun that I'm currently having to weld back to good health. The chassis has has LOADS of work now and is almost done. However, my petrol tank is knackered. It has large holes all over the top where water/mud etc can just sit and eat their way through. I don't really fancy welding it and to be honest it's probably easier to just start again!

So why fabricate one? Well there are no repro ones available, I can't even find a second hand one (which will probably be rusty anyway) and a genuine Mitsubishi one is £400.

I'm not hugely bothered about it looking original, so as long as it's the correct shape to fit in the space in the chassis I'm happy enough.

The standard one looks a bit like this:

They look to be made from 2 pressed steel sections, joined at a flange in the middle of the tank. The flange also acts as the mounting point. How do they make the tank sealed at this point? I'm thinking of a similar construction, a bit like this one with end plates:

http://www.customclassictrucks.com/...how_to_build_a_custom_gas_tank/photo_10.html#

But with a flange around the centre which would be spot welded. I have a proper spot welder. Would it be feasible to seal the tank by then brazing along the inner section of the join and around the end plates? I'd probably only have a MAPP blowtorch. What filler would be best?

I don't really want to mig external corners because it'll look horrible and amateurish. I can't TIG and don't have the facilities. The factory must have used a similar method to produce them in the first place?

I was going to go for 1.2ish mild steel if that's suitable?

 

[scotty41]

I made one for a Daihatsu four trac. just made a rectangle box, starting with a U shape, added 2 sides so they sat in 10mm each side to get a nice slow mig weld into it, I used all the old internal pipes inside the new tank.
For the sender unit pick up mount, I cut the old one out the old tank and brazed it on the new lid, the lid for the tank I made little packers and tacked them inside the tank so the lid didn't keep falling inside.
Dropped the lid in so it was 10mm down resting on the packers, again so I could get a good weld on it. took about 5hrs of messing about but it was freebee for an old friend.
Worked a treat and didn't leak, don't forget the splash pan around the pick inlet or you`ll pick up air on the corners (if its derv). I made it from 2mm h/r but that's what I had at hand.

 

[Wedg1e]

The fuel tanks on my TVR are what looks to be resistance welded: they form an overlapping seam then run it between a pair of rollers that carry the welding current through the joint...it looks a bit like 'tyre tread' or straight knurling, if you follow. That joint on your tank looks like it'd be ideal for the same treatment. Not much help to you, I know, but might explain how the factory did it
...and makes me wonder if some sort of jig might be feasible to DIY; maybe have to be powered by an oil-cooled stick set.

 

[hotrodder]

They look to be made from 2 pressed steel sections, joined at a flange in the middle of the tank. The flange also acts as the mounting point. How do they make the tank sealed at this point?

Resistance seam welding as said, kinda like spot welding but the electrodes are rollers and obviously the power supply needs to be properly butch

A plumbers torch ain't gonna be hot enough (BTUs not temperature) to braze a fuel tank and while E5 shouldn't be much of a problem brazing and soldering ain't so compatible with modern ethanol blends of petrol albeit one that can be fixed with tank sealants

ETA if you've got access to a bead roller or use something else to put some stiffness into the larger flat sections then 1.2mm is more than thick enough.

 

[Wendelspanswick]

Years ago I watched a video of an old boy who made replacement tanks for Ferguson TE20 tractors. For the seams he used lots of closely spaced spotwelds and then flowed normal plumbers solder into the joints.
I then used the same method to make a replacement tank for a friends MG TC about 12 years ago and it's still going strong. I just used a propane torch for the solder, the kind with a rubber hose that attaches to a reg on the cylinder.
The common factor with both of the above tanks is that they are oval or ovaloid (not sure if that's a real word!) in shape so there are no square corners for stress cracks to form.

 

[norlander]

is this of any use http://www.demon-tweeks.co.uk/motorsport/fuel-tanks-cells there are ali tanks for about 120 quid plus vat, obviously they are not tailor made to your project vehicle and of course you may want to do the job yourself for the satisfaction factor, but thought I'd mention the ready made fuel cells in case of interest to you or anyone else looking in.

 

[AndyStobbs]

Assume the later plastic one doesnt fit?
Having just spent an eternity making some stainless manifolds for my car, and ultimately ending up with something less pretty than I would've liked, which ironically cost more than I could've bought them for from another member on here - I would be tempted to buy a genuine tank.

At times its just easier, I had no TIG experience, no chop saw, never cut pipe at funny angles before, no plasma and there were times I wished I hadn't bothered. I could've earned the money faster than I was saving it.
But that said I still want to make more things like them, and I'm all the more experienced for it, just a pain when it ends up costing you more to get something that's not ad neat as a bought item.

 

[piman]

Hello Kafer Meister,

I think most petrol tanks have internal baffles to control the fuel.

Personally I would think it's easier to cut out the damaged area and weld a repair panel over it. I fill the tank completely with water to carry out the welding. Getting a good seal with MIG might be your problem and the slightest pin hole will obviously leak.

Alec

 

[pedrobedro]

I made one for my car from folded 18g with ends welded onto it and the hole for the neck cut with a hole cutter. I fitted two internal baffles. I've never seen baffles in a standard production tank. I drilled holes for the fuel take off and return and welded PCL pipe joiner fittings in to connect the pipes to.

 

[Bill Edwards]

You will have a struggle to make a good braze with MAPP gas, I've tried it using propane and it was just about impossible.

 

[DrNik]

You can buy some sealant that you mix the 2 components together, tip into the fuel tank and then swill it around, it makes a protective seal, fills pin holes or damage, bigger holes can be taped over, google it

 

[Kafer_meister]

Hmmm, Thanks everyone for your input. Loads of food for thought.

The standard tank is pretty simple, there are no baffles etc in it. Just an inlet, breather and a large hole for the sender unit/fuel output.

I had considered a universal type tank, but the filler neck is always in a very inconvenient place (i.e. in the middle of the boot floor). The ones from Demon Tweeks in a decent size (12 gal) are over £350! I considered a universal plastic one, but they're still over £100 and still the wrong shape.

I don't think the later ones will fit. Everything becomes much more 'packaged' when things become more modern.

I didn't consider that ethanol fuels might 'eat' bronze or silver solder brazing. Are they really that aggressive? I could just seal it afterwards, that's not an issue. As it's just for sealing purposes rather than structural does it really make any difference whether I braze it with solder?

 

[Wendelspanswick]

As you say the solder is just a gap filler and not structural so plumbers solder will do.

 

[hotrodder]

I didn't consider that ethanol fuels might 'eat' bronze or silver solder brazing. Are they really that aggressive? I could just seal it afterwards, that's not an issue. As it's just for sealing purposes rather than structural does it really make any difference whether I braze it with solder?

The E5 we currently have isn't too bad but ethanol is hygroscopic which aggrevates things, especially when you have a bunch of different flavour metals in contact with each other. We're due to join the rest of Europe sometime this year with E10 which has already caused a bunch of problems. Won't be an issue, initially at least, as e10 pumps will be labelled but whether regular unleaded e5 gets harder to find in the future is another thing as the stuff is being forced us i.e. a % of petrol has to be from renewable sources
Finding impartial data on the subject ain't the easiest thing as if it's something to do with the classic car scene you get the same doom mongering that occured with the demise of leaded while any that say it's nothing to worry about typically turn out to have used the petrol retailers association as a source. The same association that have published a bunch of papers concerning biofuels and corrosion of filling station storage tanks...

 

[Kafer_meister]

The E5 we currently have isn't too bad but ethanol is hygroscopic which aggrevates things, especially when you have a bunch of different flavour metals in contact with each other. We're due to join the rest of Europe sometime this year with E10 which has already caused a bunch of problems. Won't be an issue, initially at least, as e10 pumps will be labelled but whether regular unleaded e5 gets harder to find in the future is another thing as the stuff is being forced us i.e. a % of petrol has to be from renewable sources
Finding impartial data on the subject ain't the easiest thing as if it's something to do with the classic car scene you get the same doom mongering that occured with the demise of leaded while any that say it's nothing to worry about typically turn out to have used the petrol retailers association as a source. The same association that have published a bunch of papers concerning biofuels and corrosion of filling station storage tanks...

The internet is a funny place isn't it? It's a nightmare working out what is good advice and what isn't. I'm a pretty seasoned veteran of forums etc and I still get confused by all of the conflicting opinions.

I will err on the side of caution if I build one and coat it with sealer as well. Hopefully that'll resist the evil of E10.

 

[MrFluffy]

You can buy fuel tank bladders, which are fuel resistant and flex out to fill the tank, but I suspect they will work out as expensive as having a tank made. Ive only had dealings with them for fuel cells but I know you can have them custom made.