Fuel tank repair

[Wedg1e]

My TVR has twin tanks; when I took them out as part of an underhaul (it's like an overhaul, but underneath ) I found the left-hand one had a pin-prick hole in the top. As there was extensive pitting across the whole top of the tank I couldn't see any sense in just patching the one hole so I accidentally slipped with the plasma cutter and took most of the top of the tank away



Of course the tank was created from a length of sheet rolled, overlapped and resistance welded, so I had to either work out a way to put a step in the repair piece, or else recreate the whole overlap. If there's a difficult option, that's me, so I cut a length of strip of the same thickness as the tank and tickled the plasma-cut edge of the tank with a grinder to get as snug a fit as I could...



A few tacks kept it in place...



and a tentative first length of weld was run.



I checked with a mirror to see what the penetration was like:



and I didn't think it looked too bad so I cracked on and welded the strip in. Of course the heat of welding it along just one edge pulled it all out of shape so I had to persude it back to where I wanted it :



I finished by welding the ends into the corners



...and then cut another piece of sheet to fill the rest of the hole and match the original edge of the 'top' layer:



Some tacks and persuasion with the panel hammer later...



and it was time to get jiggy with the Tiggy !



This left just the overlap to weld... but it was here that it dawned on me I'd never tried a TIG overlap on thin sheet Only one thing for it: blag it



Looking at the inside of the overlap and adjacent butt, through the filler neck:



So, place your bets: where do you reckon the leaks will be?

 

[Wallace]

So, place your bets: where do you reckon the leaks will be?

The bottom seams.

 

[DrNik]

There is an epoxy fuel tank sealer, fantastic stuff, guy at a show had a motorcycle tank with the side cut away, filled pinholes and any dodgy areas, hey if you have a tig, should have made it in aluminium......

It's harder than you think to make something watertight, as Gerry knows,
test it with water first, nothing worse than filling it up with fuel to have to drain it and then filling with water, although filling with water helps start the rusting process again?...

 

[Wendelspanswick]

There is an epoxy fuel tank sealer, fantastic stuff, guy at a show had a motorcycle tank with the side cut away, filled pinholes and any dodgy areas, hey if you have a tig, should have made it in aluminium......

It's harder than you think to make something watertight, as Gerry knows,
test it with water first, nothing worse than filling it up with fuel to have to drain it and then filling with water, although filling with water helps start the rusting process again?...

How about test filling with Meths? I know it's still flammable but not stinky/messy/explosive? like petrol or would that cause rust as well.

 

[awemawson]

Seal the orifices and VERY lightly pressurise it with a bicycle pump to 1 or 2 psi ONLY - then dunk it in a tank of water or lather it in soapy water and look for the bubbles. It is very important NOT to just connect it to your compressor at 90 psi as if it lets go it will be nasty.

Andrew

 

[justmental]

i did this last week and well happy as when i did a pressure test on it and soapy water only had 2 little pin hole leaks in it.

 

[hotrodder]

Petrol will find leaks that water won't.

As said air is the thing to leak test with... if it's air tight it'll be fuel tight, if it fails it's a lot quicker, easier & less messy to empty again than with water.

Many fuel tanks will start to change shape if you reach/exceed 2 psi. With a decent pressure gauge and some soapy water can find the smallest of pinholes with less than 1 psi

Can't see the face in the pic but the gauge i use has a resolution of 1/4psi and can easily be read to half that. Advantages of the gauge are that i can get on with something else instead of having to get the soapy water out

If it leaks and you're the glass half full type then the soapy water goes on the capped fittings first

 

[Wedg1e]

Thanks chaps, haven't been able to reply sooner as Ive been stuck in the totty capital of the south coast for yet another week...

Yes, I was planning to use air and soapy water for leak testing; the tank has a number of inlets and outlets of varying diameters that will take some plugging but I'll think of something.