Extended range fuel tank

[Pete.]

This is my second attempt at this. The first one I made a basic mistake by not checking the pressure gauge when checking for pin-hole leaks. I had been using 5psi pressure and leak detector spray but somehow managed to put 30psi into the tank and blew it all out of shape., so I've had to get another tank and have a second go at it.

Anyway, my bike is a BMW R1100S which only carries 18litres of fuel but has a huge space under the tank where the ABS unit would live if it had one. I decided to use this space to carry more fuel.

First I had to rotate the ECU on it's mount to lay flat because usually it stands up in the middle of the space I want to use.

Next I marked out for the tank extension. It has to sit just above the ECU and also wrap around the hole for the fuel pump/level sender.

And then I re-worked the template I used to make the first tank so it would do a better job and save me some awkward welding

Then after some grinding & filing

 

[Pete.]

Hand-bent the sheet to form 3 sides of the tank

Offered it up - not too bad just a bit of fettling needed

After some grinding and filing

 

[Pete.]

Next job is to re-mark the tank to suit the actual fitted part and then mark it for bend-tabs. This is because the ally is quite thin where it's been stamped into tight corners and I managed to blow a couple of holes on the first one. Bending tabs up stops it burning back from the edge when tacking and gives a bit more tolerance since my old transformer set has no facility for a foot pedal.

I didn't actually take any photos of the tabs but it's easy to imagine. I just pulled them round with a pair of wide-jaw mole grips until I got a decent fit on the new section, then I welded it on the inside.

I found that bloody hard to do because of the awkward space and clunky wp17 torch. Also the tank ally is thinner than the new stuff in places so burned back easily especially where the tabs were small. I had to weld it on lower power but wasn't so happy with the penetration so whacked the juice up and went over it again hence the wide welds.

After that I started to weld it on the outside. I'm a welding novice so thought it best to have belt and braces, plus it looks a lot tidier. Outside welds were a lot easier and came out much better.

And that's where I'm up to so far. Should have it done tomorrow (well, today now I guess).

 

[julianf]

I was looking for a way to both show appreciation of your work, and also add the comment that i spill more fuel than that every time make it!

(20mpg landrover on biofuel, which, at some point, i too would like to add extra tanks to also!)

 

[Pete.]

Well, it's nice of you to say so but I'm never going to win any prizes for my welding, I'[m yet to finish my first bottle of TIG gas. I'll be satisfied if it looks half-decent and doesn't leak like a garden sprinkler

 

[zx9]

Well, it's nice of you to say so but I'm never going to win any prizes for my welding, I'[m yet to finish my first bottle of TIG gas. I'll be satisfied if it looks half-decent and doesn't leak like a garden sprinkler

I am very impressed Pete, you are far more ambitious than me and I am almost through my second bottle of Argon.

 

[normspanners]

I didnt realize they had separate alternator if the power ever goes you could help and plug into the national grid !!

 

[Pete.]

Made the rest of it today, first job to cut and bend the tabs along the last edge:

Then a bit of careful measuring with a framing square and some steel rules, and a card template for the shaped edge:

Next I bent and rolled the top by hand with a simple jig:

 

[Pete.]

Half way round welding the top on:

And now it's welded up:

Just got to pressure-test it, weld up the inevitable pin-holes and it's ready for fitting. The only worry is that I might have a pin-hole down in the narrow gap. This happened on the first one and I had to weld a thin strip to seal it up higher where I could access with the torch.

Soon find out...

 

[taycat]

sorry to go off, but we fitted ex-mil tanks under seat in dad's 110.
and boat tank under rear seats for diesel heater.
still got some brand new change over taps if you need them.

 

[Pete.]

Results in on the pressure test. Not so good Al

I'm pleased with the fact that I only got two tiny pin-holes in my welding on the outside, marked by arrows, but despite careful welding of the inside edge which is not accessible to weld from outside and checking over with a mirror it seems it's leaking from that joint in a couple of places so just like the first tank I'm going to have to weld in a fillet between the two sides. It's a shame because it's not easy to do and will probably not be too pretty when it's done

Incidentally I put a rule across the bottom of the tank and saw that it started to expand at just 2psi of pressure.

 

[Wallace]

Nice job, what did you do about fuel vapour?

 

[Pete.]

Nice job, what did you do about fuel vapour?

Nothing mate, the tank had no odour of fuel when I got it.

 

[skotl]

That's very ambitious - well done!

 

[Wallace]

Bummer about the awkward leak. If you were closer I'd lend you my WP9 torch if that would help.

 

[Pete.]

I have a wp9 but there's so much heat-sink in this tank it takes ages to get the welds going properly and the little torch gets too hot to hold. I'll use the WP9 to weld in this last fillet because I have long shrouds for it which I don't have for the WP17.

I'm wishing more and more now that I had a foot-pedal machine.

 

[Pete.]

That's very ambitious - well done!

Cheers, just about ready to weld the last bit in. I've drilled a couple of holes under it now too - might as well use that space for fuel as well if it's there.

 

[normspanners]

Nice job.
Just a question though why did'nt you make it like that first off? (sorry second off) I know hind sight etc but you had the same prob first time surely that changed it to foresight?
Also it helps bridge the tank.

 

[Pete.]

I did consider it Norm, but the mount lug gets in the way of welding a side plate to the seam of the tank.

Anyway, as I predicted the last bit look like a bit of a dog's dinner but leak spray says it's sound at 5psi so I can call the job done.

 

[normspanners]

Well done but can you now afford to fill it?