Right from the start of this project I knew that we were going to build a custom fuel tank, the DLRA rules state that if you are going to run a non standard fuel tank it must hold a minimum of 5 litres. This got me thinking, where else can we put 5 litres of fuel? After kicking a few ideas around we decided to run the fuel under the seat, this was done for a few reasons, firstly we would not be using the standard airbox, this would free up some room under the seat, secondly we have a lot of electrical system to hide, the standard tank position would be the best place to locate all of this equipment. With the plan set fabrication of the fuel tank could get underway. I decided to build it out of aluminium, this would give the finished product a great look, would be strong, and lightweight. It would also be a good test of my aluminium welding skills…
As the bike is using an EFI engine we needed to incorporate a fuel pump into the tank. The standard Thruxton pump is a strange shape and was not going to be an easy modification to fit in an under-seat tank. I talked this through with Triumph and they suggested a Tiger800 pump, its was ideal. I fabricated the base plate for the tank first, this is where the pump would mount.
To provide a secure mounting for the fuel pump I turned up a series of small blind threaded studs that I could weld to the base plate of the tank, this seemed like the easiest way to add a threaded hole to the tank.
All the welding on this tank was done with a TIG, by machining a flange onto the bottom of the studs I could easily weld around the edge forming a nice joint. With the base plate complete I fabricated a top plate and a front and rear panel for the tank. Both the front and rear panels are curved, I rolled this curve in using an English Wheel.
The filler cap is a beautiful aluminium part that is designed to be welded into a tank. I opted to fit it in a raised position so that the filler will be easily accessible through a hole in the base of the seat. I welded in more aluminium blind studs to the top plate to provide some rigid mounting points for the tank.
With the top and bottom of the tank complete I just had to fill in the sides with more panels of aluminium, each one was carefully rolled into shape using the English wheel. I welded it carefully to make sure I had good weld penetration through the thin sheet, this allowed all of the welds to be ground smooth on the outside of the tank.
The final tank is a great fit in the underseat area of the bike, so far its only roughly finished, I am planning to give it a nice clean brushed alloy look. I will also weld in an additional tank vent, the filler cap is vented but I am not sure that it will flow enough air so a second vent will be used just to be sure that we won’t have any problems generating a vacuum in the tank.
The big questions is “will it hold 5L”, I have no idea and haven’t had a chance to test it yet. Hopefully it’ll have enough volume, fingers crossed!