Topic: fiberglass/composite fuel tanks?

[Brandedone88]

As a guy who did it once, all I am going to say is follow the advice of Rafster and Raul.  If you are in Spain you do not have 10% ethanol gasoline.  It is a gift from Al Gore.

[jason41987]

ill have no problem carving the seat and tank out... i used to build musical instruments, a lot of electric guitars and basses which required accurate carving of the neck, and bodies... so carving this rigid foam should be a really easy task for me.. i doubt its as tough as grinding out contours in a hard maple les paul top

[jason41987]

i wonder... could i get some kind of castable foam... a mixture i could pour into a mould and have it solidify as a solid piece of foam?... because i could take plaster moulds of an original tank, pour something into it and when it hardens i can remove it from the mould, and add or remove features from the shape... such as knee dents for example before using this to make the fiberglass pieces

how would i go about doing this? or am i better off just carving the top section of the tank from scratch?.. it really might be better to get an old one that fits and make a mould of the bottom of the tank... would save me some time

[Brandedone88]

What about wax or modeling clay?   It is what guys like Craig Vetter and the other guys who were doing this work in the 70's were useing before computers.   Make a full size version and then mold it to the shape you want.

[jason41987]

hmm.. i think im going to get a pre-existing tank and duplicate it for a first attempt, then fabricate the seat shell mould from foam

[mono]

i wonder... could i get some kind of castable foam... a mixture i could pour into a mould and have it solidify as a solid piece of foam?... because i could take plaster moulds of an original tank, pour something into it and when it hardens i can remove it from the mould, and add or remove features from the shape... such as knee dents for example before using this to make the fiberglass pieces

Great Stuff expanding insulatory foam.  dries hard as a rock and is cheap.

[RAFster122s]

The reason that DOT wants a bladder is for safety reasons, asphalt will chew through a fiberglass tank very fast, then you have a fire or explosion possible. Or the rider if still with the bike could get doused with gasoline.  Lining the tank is purely for sealing fuel resistance protective layer for the fiberglass resin. It does very little to nothing for strength or fire control.
When making a mould, it will replicate every dimple and blemish of the original.  The reason you build a female mould  is so the exterior of the finished part is very smooth. It is easier to create a smooth finish for the exterior that way as your resin fills the weave and gives a nice finish. A lighter cloth for the first or second layer is used. This lessens what is called "imprint", that is where the weave of the cloth is visible in the molded surface.  This is usually a problem on vacumn bagged parts where you are working with a male part you are fiberglassing.
You also layer your cloth with 45 degree bias from the previous layer for strength.
You wont get many parts out of a plaster mould and you will have to use a mould release to get the tank to release from the plaster. It would have to be a multisecned mould of at least five or six sections.  2 bottoms, left and right side plus a top for around the tank opening. If you are going to harvest a filler opening from a metal tank you will need to account for that with a flange in your mould. So, there are lots of things you need to decide and learn about. What temperatures will the bike see, as thermal rate of expansion is different between your metal part and the fiberglass. This could cause a seam failure.

[jason41987]

so mono.. i could make a plaster mould of a pre-existing tank, put the two halves of the mould together and fill it with the insulatory foam that hardens, then i can carve knee dents and other features into the tank, and use this to make the final pieces?

[mono]

so mono.. i could make a plaster mould of a pre-existing tank, put the two halves of the mould together and fill it with the insulatory foam that hardens, then i can carve knee dents and other features into the tank, and use this to make the final pieces?

yeah that sounds like a good approach, although i'd do some small-scale experimenting with it.  since the foam expands, it does get bubbles of varying sizes that you'd have to fill in first, probably with Bondo.  it's also really sticky (it's made to adhere to all kinds of crudded-up surfaces) so you'll also need to figure out how to keep it from adhering to the plaster mould.  maybe use a light spray adhesive to put down a saran wrap liner on the plaster 1st, then spray in the foam.

**edit -- or maybe even waxing the plaster ?  not sure if the foam would stick to the wax -- just another idea (try a small glob on some wax paper).

[matt mattison]

so mono.. i could make a plaster mould of a pre-existing tank, put the two halves of the mould together and fill it with the insulatory foam that hardens, then i can carve knee dents and other features into the tank, and use this to make the final pieces?

Most whom make these just use foam purchased from a hardware store or a flower shop. Your not going to say, purchase a 3'x3' block of the stuff. You need to stack and glue it together generally to get a good sized block . Get the shape close by using an electric knife then fine tune it using a open sure form rasp. Your going to need to attach this to the frame as you go. This way you can shape it to your liking. Now you have a plug so you can lay the glass for a female mould. Once the female mold I'd done, make the male mould out of the female. The male is your tank. There's a lot of other details I left out about how to lay the glass, resin, and how to release everything, but I think you have that under control. Another good idea is to get a steel tank and just cut the bottom out, that way you can use it for the tunnel, bung and mount points. Graft the steel bottom to your fiberglass tank. The steel will also add strength . I would definately consider a bladder and a liner in case the bladder ever failed.