Modifying a (clean and new) fuel tank

[Richardj1978]

Hi all,

I'm currently looking at converting an fuel tank to take an internal electric pump, and allow me to run a previously carburettor car with fuel injection.

It should be easy enough to spot/plug weld a swirl pot inside the tank, but the area I know I'm gonig struggle with is welding in a recessed mounting point in the top of the tank to allow the pump and sender unit to be fitted.
I've done a fair bit of welding in the past but only with thick steel (3mm+), and at the moment only have access to a Clarke 151TE MIG welder to do this.

I'm worried about the thickness of the metal (being 1mm), and getting the welds fuel-tight.
Just wondering if anyone has advice on doing this, or whether I'd be mad to even bother trying this with a MIG, and should just find someone who can TIG it up for me.

Any advice would be gratefully received.

Thanks
Rich

PS forgot to add, the tank is brand new so no vapour issues.
Unfortunatley due to the age of the car, there are no replacement injection tanks out there.

 

[cumbriasteve]

You probably know what I am going to say...with something as critical as a fuel tank the weld standard is critical and if you have even the slightest doubt in your mind then get a pro..and that does not mean a garage that does welding, I would be looking for the best I could find.

 

[hotrodder]

What about an external swirl pot? Ok, bit more plumbing involved but it'd save you having to cut up your tank.

The majority of steel tanks have a 'terne' (traditionally tin/lead these days i think tin/zinc) coating on the inside for corrosion protection which'll obviously be damaged. In the next year or so the ethanol content of UK petrol will be raised from 5% to 10% which may not help

Unless you'd rather mod the tank yourself it'd probably be easier and cheaper to pay someone... welding skills are mainly down to practice and pinholes/modern corrosive fuels can be delt with by using a tank sealant for example http://www.frost.co.uk/how-do-i-repair-my-fuel-tank but you'd still be looking at knocking up fittings to leak test the thing

 

[Pete.]

Cut a round hole in the tank to receive the pump, drill holes and fit rivnuts then mount the pump onto a plate then bolt the plate to the tank with a rubber sealing gasket.

Actually, to save yourself the trouble, find a used internal pump from a motorbike like a 2001-onwards Hayabusa which comes complete with mounting plate and sender attached plus pressure relief valve built-in. All you have to do is make a hole then.

 

[barny]

What car is it for?
I know this mod is done when putting fuel injected engine in mk1/2 fiestas

 

[Ducati]

Hi all,

I'm currently looking at converting an fuel tank to take an internal electric pump, and allow me to run a previously carburettor car with fuel injection.

It should be easy enough to spot/plug weld a swirl pot inside the tank, but the area I know I'm gonig struggle with is welding in a recessed mounting point in the top of the tank to allow the pump and sender unit to be fitted.
I've done a fair bit of welding in the past but only with thick steel (3mm+), and at the moment only have access to a Clarke 151TE MIG welder to do this.

I'm worried about the thickness of the metal (being 1mm), and getting the welds fuel-tight.
Just wondering if anyone has advice on doing this, or whether I'd be mad to even bother trying this with a MIG, and should just find someone who can TIG it up for me.

Any advice would be gratefully received.

Thanks
Rich

PS forgot to add, the tank is brand new so no vapour issues.
Unfortunatley due to the age of the car, there are no replacement injection tanks out there.

Hi Richard.

What car / engine is it ?

Which fuel injection system is it ?

A few reasons why I ask.

Early systems used a pressure regulated fuel rail with the fuel being returned into the swill pot.

Later systems do away with the return line, correct fuel rail pressure being maintained by the ECU modulating the pump speed.

Hope you have thought out which pump safety cut out feature to go for, inertia switch, tachymetric relay, or if a newer system, again ECU controlled.

It should be easy enough to spot/plug weld a swirl pot inside the tank, but the area I know I'm gonig struggle with is welding in a recessed mounting point in the top of the tank to allow the pump and sender unit to be fitted.

Many swill pots were welded to the tank bottom whilst it was in two halves, will you be able to get the correct size swill pot through the fuel pump access hole, in the correct position and weld it ?

A work around could be to find a vehicle that used a combined pump / sender unit / filter / swill pot.

Use this, cut the mounting flange from an old tank and weld it into yours, you would obviously have to have an assembly to fit the depth of your tank.

PS forgot to add, the tank is brand new so no vapour issues.

It's surprising how many folks are frightened of the big bang when welding used petrol tanks, though I must say fear is a great protector of life and limb.

I've lost count of the petrol tanks I repaired by welding over the years, my usual sequence being, (1) drain and remove tank, (2) pop the steam clean lance in for 10 mins, (3) organise bungs for the various orifices, (4) arrange tank with repair area uppermost, (5) Fill with water via one of the bung adaptors, (6) once the tank was full of water and it was flowing from the repair site, turn off the water, cut out the area with gilbows, or air nibblers, then put a match to the layer of petrol floating on the water, drop the water level enough not to interfere with the weld then weld away.

Have you a local fuel tank repair company you could approach, most are small one bands but have a wealth of knowledge ref. fuel tanks.

As Hotrodder said, you must re-instate the inner tank corrosion protection, as he also mentions Frosts have the materials.

Other than impact damage, many of those I repaired over the years were to corrosion of the top of the tank, from inside, caused by condensation, mainly on cars used as a shopping trolly with a tenners worth of fuel put in at a time.

Quick word of caution ref. electric fuel pumps.

Whilst most are not much more than glorified screen wash pumps, full of petrol whilst working, the petrol provides both lubrication and cooling, the brushes happily arcing away in the petrol, a non combustion situation.

Remove the pump from the tank, leave it somewhere where some of the petrol drains out, the petrol is replaced by air, test the pump............bang.

No, before you ask, I haven't done it, but I know a man who did.

He had a Bosh K Jetronic go pop on him whilst testing it.

Don't know if you know these external pumps, but they are built like the proverbial brick ...... compared to the in tank pumps.

Nice to see another project.

Any photo's ?

 

[Richardj1978]

Wow, thanks for all the info guys. That's quite a response .

The tank is for a mk3 Cortina, which I'm hoping to do an engine transplant on in the not too distant future. I've got a cut-up tank from an old Sierra that has the swirl pot, pump and pump mounting intact which I was hoping I could graft in. Still not settled on the engine, but it probably safe to say it will be running with a pressure regulator and fuel return.

I'm considering asking someone with a bit more experience to do it, but can't anyone near me who does this kind of work. I'd ideally like it welded in nice and watertight without any tank sealers etc being used to fill pinholes, as I've heard bad things about these not liking ethanol based fuels, and peeling off.

Hotrodder - Yeah, I'd considered the external swirl pot and pump route, but it just seems like a lot more "moving parts" to go wrong, for not much gain.

Pete - Cheers, that may actually be an easier way to tackle the problem, rather than try and weld in some new metal. I might try a bit ore digging around this.
The big problem would be getting the swirl pot in, because as Ducati points out, the entry hole for the pump is likely to be a lot smaller than the swirl pot.

Ducati - A fuel cut-off/intertia switch is defintiely top of the list when I come to install it. The idea of being stuck in the crashed car, with the pump still running is something I don't even want to think about.
Thanks for the advice on testing the pump as well, I have to admit I hadn't even considered there'd be an issue running a pump outside of the tank.

I think my biggest worry about doing it myself, is that I've never welded anything to be water/fuel tight, esepcially with really thin metal and can imagine it being a nightmare.
Would brazing the pump mount be a better way to do it?

I'll try and get some photos up soon, if you're interested.

Thanks
Rich

 

[hotrodder]

I thought one of the ideas behind tank sealers was they're more resistant to ethanol* blends than the standard terne coatings? A guess but i'm thinking some of the stories of the stuff peeling off and clogging everything may be as much to do with improper application as anything i.e. a quick rinse out before sloshing the stuff around ain't gonna cut it

The size of the cutout needed in the tank obviously depends on the layout of the donor kit... last time i did this we basically cut pretty much the entire top out as there was mucho reworking needed to get everything right. On the other hand using a pump like Pete's suggestion or one of the 'drop in' types (outlet, return etc all included) would need a smaller hole and you could maybe even fabricate a bolt in subassembly that includes the pick up baffle. One of my pet hates with this sort of conversion is a fuel gauge that's so innacurate it's almost pointless, float arms can be bent/modified if they're they're the lever type but obviously the sender needs to be compatible with the gauge too

This is how i usually baffle the outlet when scratch building a tank (incomplete in that the return is directed into the pot and there was a top added)...




I'm not sure what the stock Sierra set up is but most of the tanks i've modded have had a pick up baffle like this one. Recently had to repair the tank on the daily driver which is probably the most complicated i've come across... http://www.w124performance.com/service/w124CD1/Program/Engine/LHIS/47-0010.pdf What the pdf doesn't show is that pot is mounted 5mm or so off the bottom of the tank on a horizontal baffle with the fuel filter bolted into it via the bottom of the tank

Pros and cons to brazing... an air tight joint would be easier than MIG on thin sheet but distortion could potentially be a bigger issue and more clean up work due to the flux

*talking regular pump fuel blends, not the full fat e85

 

[Pete.]

Pete - Cheers, that may actually be an easier way to tackle the problem, rather than try and weld in some new metal. I might try a bit ore digging around this.
The big problem would be getting the swirl pot in, because as Ducati points out, the entry hole for the pump is likely to be a lot smaller than the swirl pot.

The pot on the bottom is the bike pump's 'swirl pot', it protrudes down from the fuel cell. Seems to work just fine on the average sportsbike with all manner of possible wheelie abuse and throwing about, can't see why it wouldn't be okay as it is in a Cortina. What fuel pressure do you need - these are set at 43psi IIRC.

 

[hotrodder]

It probably would be but the layout of a car tank (typically very wide and/or long relative to height in comparison to a bike tank) might be enough to cause problems in some situations? Another potential issue would be the pump ending up in a vunerable position but that obviously depends on where the tank is sited