Topic: fiberglass/composite fuel tanks?

[jason41987]

i was wondering if its possible for someone to make a composite or fiberglass fuel tank?... i read somewhere that regulations require the inside of the tank to contain a bladder, as the fiberglass itself isnt safe for contact with gasoline?..

so i had the idea of taking an original tank and making a mould of it, possibly out of plaster or some other material... then using the bladder material in a couple layers, inflate two bladders inside the mould with a layer of adhesive in between.. when it hardens, the bladders will be solidified in the shape of the fuel tank, and then they can be fiber-glasses

thats just one idea i had... one of the reasons i was thinking of this is because of how easy original fuel tanks are to tent, ding, and rust... would be interesting to have a lighter, and more durable alternative

so.. what do you think of this idea? and does anyone have any of their own for making a fiberglass tank?

[bjbuchanan]

I'm gonna be the douche but you really need to search in the left search bar.

Tanks are doable but can be complex molds to make, just think about how many mounts/bosses you have to include on the mold or tank

Another thing is that it will have to be sealed, no option. ethanol in the fuels will make it gummy in almost no time so add that to your costs

Consider that it costs 50 to 60 in materials just to make a decent bump seat and try to imagine what it would take to make something way more complicated and larger

[camelman]

I'm currently laying up some drop in fiberglass and carbon fiber tanks. I've been planning on it for a while, and finally got a reliable aerospace engineer to finish it. We aren't using bladders since he's never needed them for the carbon fiber passenger and stunt planes he has built. Hit me up with a PM if you are interested in talking about them.

[Rookster]

Another thing is that it will have to be sealed, no option. ethanol in the fuels will make it gummy in almost no time so add that to your costs

This is not universally true.  Fiberglass tanks made of polyester or vinylester resins will break down from modern fuels but newer epoxy resins will not.  The epoxy resins are more expensive and increase the cost of the tank but they can and are made to be compatible with modern fuels.  Glass from the Past makes fiberglass tanks of epoxy resin that do not require a liner.

Scott

[bjbuchanan]

You are right about it not being an absolute for sealing I just meant in most cases, the easy to get materials. You can hit up a fiberglass or body supply place and easily get what you need for a couple more bucks i guess i just assumed too much given the question

[jason41987]

umm, thats why carbon fiber and fiberglass tanks tend to have that bladder inside, and in most places i believes its a DOT requirement for composite tanks and if bjbuchanan had read what i said, my post was about my specific idea of inflating two bags, one inside another with a layer of adhesive in between so that these bags would take on the shape of the fuel tank, once the adhesive hardens them into a solid shape you could apply the fiberglass or carbon fiber directly to the outside of it and itll avoid you having to cut the composite tank to get it off the mould

not that it would mater if you had to cut the composite tank to get it off the mould though, most places require a fuel bladder inside composites, so there wouldnt be much worry of a leak...

i dont think it would be all that difficult to make a mould of a pre-existing tank, or for that matter, carve one of your own design out of foam, then coat it with a resin to harden it and use that

[Raul CB750K1]

Just fyi, I have a 30 y/o bike with a fiberglass tank, and it has not leaked as of today.

From what I know, the trick is to "close the pore", and it is done flaming the outside -the exact procedure I don't know-.

I have recently done some custom fiberglass sidecovers for that bike, and the resin shop told me I had to use acetone to clean the resin- it is the only solvent that will clean it. That means the resin is inmune to gasoline.

Doing fiberglass work is a dirty work, but I have discovered a new world of "artistic expression" that lets you fabricate almost anything. I have also considered doing my own tanks out of fiberglass.

[jason41987]

what do you think would be better?... a fiberglass tank? or a plastic one made of gas-safe plastics?

[Raul CB750K1]

what do you think would be better?... a fiberglass tank? or a plastic one made of gas-safe plastics?

I think the equipment to have in order to make a fiberglass tank is almost none, while to make one out of plastic you probably need some kind of "pressure mold", in where the plastic is like a tube that is heated, and then inflated in such a way that it gets the form it is contained into. That is, fiberglass is great to make one-offs.

That being said, I think a fiberglass tank would have much more strenght. My gasoline canister is made out of fuel-resistant plastic, but I can distort it with the force of my hands. I could not do that with a fiberglass canister. In terms of "safety", both would be the same as long as they don't leak, but probably the heat of the motor would distort a plastic tank, but would not a fiberglass tank.

[MRieck]

what do you think would be better?... a fiberglass tank? or a plastic one made of gas-safe plastics?

Ducati and Aprilla (I think) have had a lot of problems with plastic tank expansion secondary to the ethanol in fuels.

[jason41987]

i think what i might try, is soaking gauze in plaster... then tightly wrap the fuel tank with this and let it harden... cut it off in a top and bottom half from the original tank and use these as moulds for the fiberglass... i could just bondo up the holes or dings in an old messed up tank i could buy for cheap... i think this is the route im likely to go

[Raul CB750K1]

The best approach is to make a mould for the the top, then a bottom, and then put them together with more fiberglass. That way you put the junction out of sight.

Finish of the mould is not crucial as you can always bondo the tank. You should provide for the tank fill hole, petcock and specially fixings. Embed metal parts where strength is crucial.

Here some pictures of the customs sidecovers I made -for another bike-. I needed some slightly shorter in the front.

First make one out of plaster




With it you make the "negative" mould.



For a sidecover I just lay 2 layers




Cut to size




Add fixings with another piece of fiberglass and resin





Bondo, sand and paint

[jason41987]

what would you suggest for making the mould itself?... i had the idea of coating gauze in plaster and wrapping it around the tank like a cast, then cutting it into a top and bottom section and using that

also, what would be the recommended means of adding threads for the cap, and installing the petcock?

[Raul CB750K1]

what would you suggest for making the mould itself?... i had the idea of coating gauze in plaster and wrapping it around the tank like a cast, then cutting it into a top and bottom section and using that

also, what would be the recommended means of adding threads for the cap, and installing the petcock?

If you want to make a custom tank, just use any material to shape it, and then make the mould out of plaster from it. Just remember you must be able to "unmould it", therefore the shape must allow to remove the piece once dried.

For the tank I would suggest buying a beaten-up tank, cutting its filler as well as the petcock threaded hole and "transplanting" them into the fiberglass tank. Just use as much sheet metal as possible around them to maximize the strength.

[jason41987]

i have seen some tanks that had holes rusted in them, or were dinged pretty badly... could use body filler on the holes and dings and make a mould from that, then salvage the section you mention for the cap and petcock as you say... however, i wonder if i look around if i could find an alternative to salvaging these parts from the old tank made from better materials, like stainless steel for example, and fiberglass them into the tank?

[mono]

Sure, why not?  I've seen multiple people use the bottom of old tanks and fab fiberglass tops for them.  Needs a final liner, but no big deal.  No reason you cant use a filler cap the same way..

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[Brandedone88]

This is an interesting thread, but I am going to have to comment on your fabrication techniques tho, because the stated technique will result in gas seepage.  The stated technique with the cloth was used to produce the tanks on the British bikes of the 60's.  Today with the ethanol will cause seepage and holes.  Although I will admit that it was effective.  One method that we use to do was to get a block of stryfoam and make the pattern out of that, and then pore the resin over the stryfoam.  Then pour gasoline in the tank, which would be eaten by the stryfoam.   If you do use the cloth technique use an epoxy resin, as it won't be eaten by the ethanol.

[jason41987]

thats an interesting idea... using a foam that gasoline would actually eat away at... but i bet it doesnt have to be gasoline.. any chemical that would eat through foam but not the epoxy should work

im not going to pattern mine after a pre-existing tank... what ive decided to do is get some measurement tools out, and backwards engineer the top half of my frame and then re-create the top half of my frame in autodesk inventor, this will allow me to create my own tank and seat design, and ensure a proper fit before ever cutting into a piece of foam

i believe acetone will dissolve urethane foam... hmm, i wonder if i could brush a resin into the outter layer of the foam... a resin that would make a superb barrier for modern gasolines,... perhaps an extra layer of epoxy, and let it harden before applying the fiberglass... then when its finished pour some acetone in to dissolve the foam leaving behind the fiberglass shell and that extra layer of epoxy for a liner

i could even stick the filler cap threads and a bushing for a petcock directly onto that initial layer of epoxy, or between layers of fiberglass and drill out the hole once its finished... i really like that idea, im going to have to run with that one because i think its the simplest solution, and doesnt require me to fiberglass two halves of a tank together

another question i wouldnt mind getting an opinion or two on.... i looked at the price of carbon fiber cloth as well as fiberglass cloth, and the carbon fiber cloth wasnt too much more... while im in the process of fabricating a composite tank, would it be a good idea to spend a little bit extra on materials and go with carbon fiber instead?... if i do go with carbon fiber.. im going to use it on the cafe racer seat pan too, and make fenders to go with it... all this should really lighten up the bike too

[mono]

Acetone readily dissolves regular Styrofoam, however after seeing a couple threads from people who used the "dissolve the foam" method, i would highly recommend a different method.  At least i would never try it that way.

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[jason41987]

so... would it be worth spending a little extra for carbon fiber instead?.. or is there not enough improvement in the materials to justify a bit more cost?

[Raul CB750K1]

so... would it be worth spending a little extra for carbon fiber instead?.. or is there not enough improvement in the materials to justify a bit more cost?

Probably you could cut your teeth with the fiberglass -it's cheap- and move to carbon fiber when you have mastered the technique.

Doing the lower part is the tricky part: shaping it to accomodate to the frame tube etc. It's a good idea to use the lower of a tank and build the rest with fiberglass. Otherwise, you could use the lower of a tank as a mould- you either fabricate a "negative" first, on which to lay a "positive" later, or shape following the internal countour, in the safety that it adds the sheet metal thickness so it will have no problem accomodating the frame.

I can't tell wether gasoline in Spain have ethanol or not - I have this bike since 2008 and have had no seepage so far.

[jason41987]

if i design the tank from scratch, i would print out a bunch of cross-section images in 1-inch or half inch increments, and trace each image onto a piece of rigid foam of that thickness, then glue them all together and sand the rough edges.. should be able to construct the bottom profile decently with that technique

[mono]

if i design the tank from scratch, i would print out a bunch of cross-section images in 1-inch or half inch increments, and trace each image onto a piece of rigid foam of that thickness, then glue them all together and sand the rough edges.. should be able to construct the bottom profile decently with that technique

+1 -- that sounds like it'd work really well.   

[RAFster122s]

Read up on the mold making techniques and materials. Definitely use PVA (polyvinyl alcohol), a mold release agent, for the mold as you will need more than wax can usually handle for large parts.  Gasoline and foam is a nasty mix and with a 4-6 gallon design it would take a good amount of gas.  If the glass/epoxy isn't cured, then it can be succeptible to attack/softening.
Kevlar can't be exposed to UV and it is really best if you paint over carbon, it better protected from uv aging. Light colors are best as a hot epoxy fiberglass or even carbon  will often soften with higher heat levels.

[jason41987]

in all likeliness, i would probably make a single mould, and with it form a top and bottom section for the tank, then thin the edges a bit so i can fiberglass the halves together... this makes removing the mould much easier, and allow me to save the mould for making a new tank should i ever need one...

just think.. for the idea of printing out cross section images to cut into the foam, glue together, and smooth out, i could even take a perfectly modeled 3D car model off a popular racing game, convert the model and upload it into my solid modeling program and do the same to accurate reproduce the car body of nearly any car ever made ... at some point though, later on with the skills i learn with fiberglassing, i would actually like to design a car from scratch and build it... but thats a few years off