Building a new fuel tank
|The first fuel tank that I
fitted was a 12 litre plastic boat-style tank from K&M. This was
OK, but because it was fitted
underneath the seat, it meant that the seat ended up being too
high and too wide. I had always planned on fitting a custom made tank,
modified seat, so Spring 2005 was the time to make the changes - in
the race season.
Asking around, I found that the TZR powered craft used around 6
litres or less per race, so I reckoned I needed a tank of around 7
litres capacity. I found a filler neck and cap machined from aluminium
from Randall Motorsport,
which I reckoned was a bargain at £10,
which meant I could maybe make a long cylindrical tank to lie
underneath the seat. In order to kep the seat low, I needed to keep the
diameter down, so I looked at a range of dimensions.
The best compromise seemed to be 140mm diameter by 450mm long
with a capacity of 7 litres, which would weigh around 1.3kg when
Allowing 40mm for the filler cap, this meant that the top of the seat
around 180mm above the floor. I ordered a 2m x 1m sheet of 2mm thick
aluminium (in 5251 alloy - a harder grade than I had used before) which
would be enough for 7 tanks. At £35 a sheet that's just £5
per tank. I rolled the sheet into a cylinder using a mangle roller and
cut out a couple of cylinder-end blanks, and while I was at it I rolled
a spare to practise on.
I was not sure that I could MIG weld aluminium as thin as 2mm,
gave it a try with some flat sheet. With a backing piece, the weld
itself was fine, but the
sheet distorted very badly. I needed another approach. Talking it over
with the guys in work we came to the conclusion that I needed to lap
the edges to be welded, clamp
the sheet firmly to a strong backing piece to prevent it lifting off,
tack weld it at 2" intervals, and let it cool between weld runs.
A cylinder would also probably warp less as it is inherently stronger
than a flat
What about baffles? Under the massive(!!!)
acceleration that I am expecting, would the fuel end up
sloshing to the back of the tank away from the pickup pipe? Maybe I
should add some internal baffles? A couple of discs of 1mm sheet held
in place by a lengthways strip would probably do it.
|I used a length of 30mm
square section stainless steel tubing as
the backing piece, clamping it at the ends, and screwing it down in the
middle. This all worked a treat, and by doing a quarter of the
at a time, and
allowing it to cool between runs, it all went well.
Once the seam weld was finished, the backing piece could then be
removed and the screw holes could be welded up at the end.
||The end discs were recessed
into the cylinder by around 10mm. To provide a backing piece
for the end discs I wrapped a strip of thin
stainless steel sheet around the end of the cylinder and held it all in
place with a couple of jubilee clips in series.
Welding into a V is always easier if you can adjust the work so that
the bottom of the V is at the lowest point, so I angled the practise
around 45 degrees to the horizontal. This proved to be too steep as the
end disc melted through very quickly. Adjusting it to a lower angle,
was far more successful.
Having finisished welding both ends of the cylinder I then thought
baffles again... ah. Fortunately there are other ways of
preventing fuel movement - such as filling the tank with foam cubes (Merlin Motorsport) or
even stainless steel wool apparently.
I tested the welding around the ends by pouring some soapy water into
the recess and blowing into the screw hole. I couldn't see any leaks
in either end so things were looking good. Although the welding had
gone well, I wasn't confident enough to tackle adding on the filler cap
and the pickup pipe, so I asked Nigel in work if he could finish things
off using the TIG welder.
||This is TIG expert Nigel
Jarvis. Nigel TIG welded the filler
cap and the fuel pickup pipe.
Once Nigel had welded the filler on he let me have a go on a practise
piece of aluminium. It was very
difficult at first - especially as he "forgot" to turn the gas on! Oh
how we laughed...
With the machine set up properly (that's half the battle) I appreciated
that TIG is much
more precise than MIG as it allows you to vary the heat and filler
metal separately, whereas with MIG, the filler metal (the wire) carries
electric current (the heat) so it's largely either on or off.
With the filler and pickup pipe welded in place I drilled out the hole
in the tank, inside the filler neck.
Once the tank was finished I gave it a quick grit blast to clean it up,
then sprayed it with etch primer and green gloss.
Total cost of parts and material used was around £20.