I finally got round to attempting an underseat fuel tank for my NC30 project. With a rough idea of what I want to achieve I start by making a big block of foam from which to carve out the shape of the tank.
(You get some really cool shapes formed if you put too much expanding foam in the box!)





With the foam then roughly the right shape (and fitting into the space I have available) I apply double-sided sticky tape all over to hold a layer of release film. This will mean that I should be able to easily remove the foam when digging it out. With everything wrapped up it is off to be dressed in carbon...




The tank is made in two parts which will be joined together.
The foam is carved out, and then the tape/film just pulls right out, nice and easy with nothing left sticking to the inside.




The two parts allow me to work on the inside of the tank and prepare all the fittings.
I include a cap from an old oil bottle, an MX style breather and fuel in/outlets. Due to the complex shape I also figure that I need a number of extra pipes to stop the air getting trapped.


With everything joined together and sealed up all that remains is to secure to the bike. At this point in time the exact fixings are undetermined but I have a few ideas.
The tank will hold 6 litres in total, which should be enough for one race session. This will be coupled to another tank in the normal place, which will allow the use of the normal filler cap and more storage if needed for longer 'trips'.



To Do:
Basically finish the tail section, this includes making the rear fairing from carbon, then putting together something to fill the gap around the tank and fairing.

So, why do this?
Well, the fuel in a bike weighs quite a lot, and normally it is high up over the engine. In theory, mass centralisation is a good idea so lowering the height of the bulk of the fuel should lead to better handling.
With the original fuel tank gone and replaced by a carbon shell, this allows for modifications to the airbox and space for electrics, whilst still leaving some space for a small fuel cell.

Chris

nice work !

you're making this all look temptingly easy.. however i suspect a useless sticky mess would be the result if i attempted similar

looking good chris, how do you feel about the battery being right next to the fuel cell?

keep the up dates coming .

Looking good!

Will you be sealing the inside or using a bladder? (It's an outrage...!! :D )

Drunkn Munky wrote:how do you feel about the battery being right next to the fuel cell?

I was not worried about it until you said. What is it about the proximity that I should be worried about?
If it is just the possibility of rogue sparking then I will look to provide further barriers between the two, and to better cover the +ve terminal.

Stickshift wrote:Will you be sealing the inside or using a bladder?

I looked at several tank sealing products and came to the conclusion that they were all epoxy based. After some tests with the epoxy resin I am using for the carbon fibre I am happy that it is also petrol proof, so I just gave the inside two coats of this.

I thought the bladder suggestion was a good one. I would have leaned towards this type of inner. If you was unfortunate to have an accident and the new tank split or cracked the bladder would retain the fuel regardless of the damage to the external body. How close is the new tank to the exhaust pipes? Have you had a look at the CBR600RR to see how they have positioned their tank and exhaust routing? that could provide some pointers.

Bike looks fantastic by the way and no doubt this will turn into a success. Keep up the hard work.

+1 on bladder/ bag tank, if you drop it the and subframe takes a beating chances are that carbon tank will split and if fuel goes over the batter and shorts it... bye bye bike

In the event that you do split the small tank, I think that exploding fuel will be the least of your worried. My last 2 crashes on the track did nothing to the sub-fame. Fixed re-sets and crash bungs did a good job and my sub-frams was longer than the one you have fitted. So long as the tank is 100% sealed and that fuel won't affect the structural integrity of it I'd say leave it as it is but put something between the battery and the fuel.

Personally I wouldn't be too bothered about trying to do anything to the battery to isolate it from the fuel cell.

Look at the other pics (the second one from the bottom in particular) the standard fuel tank is sitting over the top of the battery - even closer than the new fuel cell under the seat!!

Plus as Viper says - not a great deal should happen to the subframe in a crash - especially when it is so short (and good looking might I add!) so if someting does happen to that area of the bike its likely that it will be a big off.

Cheers
Smev