I've been planning a lot for modifying my rear seat and was going to build a fiberglass seat,  I think I easily am capable of making a seat that looks great,  but I've heard that gas tanks are a whole different thing given the gas factor and air tight, etc...  but I've gone through many threads on fiberglass gas tanks and I really think I can pull it off.   My main questions would be what are the exact resins/hardeners,  types of fiberglass (or even a thin layer of carbon fiber) and others things necessary to make this work.   I know I need the inside with a protective coating against the gas of course,  but I guess I'm just asking,  outside of a normal fiberglass build,  what do I have to do extra or different?

I'm a complete noob with fiberglass but a fiberglass gas tank sounds dangerous to me.  Do they actually exist?

That sounds even MORE dangerous!  One rock with an attitude and you've got a crack and a fire.  

That seems to be a large portion of the aftermarket new cafe racer style tanks I find.   For instance Dime City Cycles has probably more fiberglass tanks then metal ones.  

I mentioned using a thin layer of carbon fiber also.   Wouldn't that also make the tank more solid or safer?   Like sandwich it in between the fiberglass?

I really want to make this work I just can't pay $400-$500 for a new tank....  And that's for a fiberglass one.   I'll see the same tank made of aluminum or something for $700-$1,100!?

v-pilot wrote on 04/16/14 at 18:09:54:


I've rarely seen that, in fact I just went to Dime City Cycles website and looked at their fiberglass tanks and not one has that disclaimer.   They are made specifically for a custom build for street bikes.   I don't even see one of them that specifies it's for racing applications only.

Yea some BSA tanks were fiberglass from the factory in the 60's as well as a bunch of Ducati street bikes had fiberglass tanks in the 70's early 80's, along with a lot of after market café style tanks.  From what I understand based on my knowledge of boat fiberglass tanks it's the ethanol that actually eats away the resin. The hardest part is sealing the tank lining properly at any egress/ingress points, once any gas/ethanol was given the opportunity to leach in behind the lining it would wreak havoc on the actual tank from the inside out.

Expand your search of knowledge on fiberglass tank building to the marine community as well, most tanks are plastic or aluminum now on boats, but there are plenty of older boats with fiberglass tanks which people are maintaining still  

I wont address the "It cant leak" part of it, but just the finishing of the surface to prep for paint. If you dont have experience in working fiberglass & sanding it, then before you spend the time & $$$ building a tank, I'd suggest you get some fiberglass & resin & make something, a box, heck, maybe just glass a cardboard box up. YOu can slice a coupla places on one side & glass hinges onto it, finish the cut, drill & bolt the hinges, make a little parts box or something,, But lay glass on thick enough to make it solid enough to sand on & learn a little about how glass acts. Keeping fresh paper on your sanding tools is important with that stuff,,
I guess something more or less the shape of the tank would teach ya more..Flat surfaces are the hardest, because any distortion will show up with a light across it, Compound curves are challenging too. & the tank has plenty of those,
Finding a high spot is part of it,, knowing which way to move the sandpaper to kill it is crucial. Sand Off of the high spots & onto the low spot youre blending to,Dont lay a sanding block on top of a high spot & scrub back & forth, Push the block off the high spot & do that in every direction that it needs blended. Once youve got it all "made" & out of the forms, remember how thick the walls are. Dont go sandin it too thin,, There is a "Bondo"( NEVER buy Bondo products made BY Bondo) type product specifically for glass,Youll need to practice mixing & getting the hardener right,,When you have "Bondo" mixed differently they are harder or softer & sand differently, BEGGING to create wavy places. Mixing the hardener for the glass,, dont want it too "Hot",, I think it makes it more likely to crack,,Like epoxy, you can determine the Set time by how much hardener you use,,Too little = a MESS,, So, Buy enough glass & Stuff to play around & learn, play with the filler
You can use a paint paddle to Spank the sandpaper & unclog it, but once its tired, ditch it,, youll be pushing too hard to smoothly blend.
Early on,you can get away with using tired paper,, but once it is getting close, you gotta keep sharp paper on it,,

I Never liked working glass,, especially patching on old glass. Fixing a "Vette" is a Huge pain,,

uigiroux wrote on 04/16/14 at 18:22:20:


If you check out Airtech Slipstreaming they say that about all their tanks.  They make some really nice stuff.  I'm building a Dicati 250 as a Paul Smart Imola tribute bike and what I've gotten from them is nice