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Al Eckstadt
Al Eckstadt
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I'm just asking this out of idle curiosity.
I've never had to deal with a glassfibre petrol tank or oil tank (yet) but I may soon have to, as a unit single project has come onto my radar recently.

Now I've studied engineering and manufacturing technology to a point, so I've got a very good idea of how most components are produced.
I can understand the virtues of making something like sidepanels out of GRP, using female moulds.
A little labour intensive (using hand lay up) but very low tooling costs compared to injection mouldings.

But how do you make something like a fuel tank out of GRP ?
Are they moulded in separate sections and then bonded together ?
Or is some special technique used to produce the hollow moulding in one piece ?
I'm genuinely clueless
But I think that if I know how something is made in the first place, I might gain some insight into how to do repairs etc.

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the GRP-tanks are made in two parts. top half and bottom half, then bonded together.
and that's where mine split after using modern fuel and leaving it in the tank for a rather long time.

so I bonded it back together again and use the modern fuel, only when the bike is not used for 2 days or more I'll drain the tank.

regrads A

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Thanks for that.
I did a bit of Googling myself and learned that you're supposed to carve out a replica of the shape you want from Green Floral Foam.
Yes they do sell it on eBay but only in house brick sized lumps its going to take about £20-30 worth all glued together for a decent size tank.
After that it's a case of making a pair of female moulds around it.
Exactly how to split the moulds and how to join together the two tank halves seems to be shrouded in mystery.
Loads of issues with resin types that are fuel resistant and ethanol is the villain of the piece as usual.
I see that BSA soon returned to steel tanks after a couple of years of GRP.
I wonder if this was due to practical issues or done on the advice of the lawyers ?

It has occurred to me that it might be a useful way to get a spare export tank for my OIF A65.
I've got a rough original that will filler and paint up OK.
But I've always been told that these tanks have a terrible reputation for splitting.
I really wouldn't want to pay £300 for an Indian made tank just to find out that it's true.

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One of my pals recently made a f/g tank using special epoxy. Lots of work. Beautiful result. started to leak soon after putting fuel in it. Do not waste your time/money going down this path. Or, use only non ethanol fuel. PRT

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"Or use only non ethanol fuel."

OR. use an aluminum or steel fuel tank.

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My B-25 Starfire ethanol melted tank was a 2 piece. Like the others go with steel or alloy

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Thanks for all the good advice.
A quick browse on eBay shows a nice selection of steel Starfire tanks (presumably made in India)
TBH I'd rather go for an original BSA item and spend a little more time on refurbishment.
At least the supply of cheap Indian tanks keeps prices down.
I suppose that if you want the correct '67 - '69 oil tank you just have to have GRP and like it.

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Steel oil tanks were definitely on the 69's, they had a fibreglass cover over the steel oil tank, so that would give the look of the earlier FB oil tank.

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Originally Posted by Irish Swede
"Or use only non ethanol fuel."

OR. use an aluminum or steel fuel tank.



Just given me an idea, I'll need a fuel tank for my A50 racer (when it eventually happens) Option being that I could metal bash a tank of sorts and make a fibreglass cover, didnt the hurricanes have something like this, or was that the aftermarket version?


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Originally Posted by pushrod tom
One of my pals recently made a f/g tank using special epoxy. Lots of work. Beautiful result. started to leak soon after putting fuel in it. Do not waste your time/money going down this path. Or, use only non ethanol fuel. PRT

did he hand lay-up or use a vacuum bag ?


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Fibreglass is the least suitable material for a fuel tank. The resins dry out over time and the tank becomes porous, Fibreglass is prone to weakening through vibration. Just look at any fibreglass car a few years old, the bodywork is full of cracks.
A fibreglass tank is easily damaged in a minor accident spilling fuel

I bought a Greeves challenger a few years ago, it had not been used for many years (long before ethanol in petrol), The tank was mushy and leaky underneath


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Obviously buying a used GRP tank for my unit single project would be a false economy unless it was virtually free.
Far better to save up for a good steel one instead.

However I would still consider a GRP tank as a stop gap measure.
I've seen rusted steel tanks with rust perforation patched up with tank sealant (masking tape across the holes until the resin cures) then given a very expensive paint job.

A fools paradise.
I think that I'd put my faith in a GRP copy rather than do something idiotic like that.

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Q, It was hand laid. They loved the shape and are making an aluminum fuel cell and will use the Fg as a cover.

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Originally Posted by pushrod tom
Q, It was hand laid. They loved the shape and are making an aluminum fuel cell and will use the Fg as a cover.

they may have have had better results with one of the various vacuum bagging techniques.
The process sucks the air out, during the wet phase, for a dense void free product.
... Or may not... At least not on the first try.

There are some Excellence composite tanks being made.
[Linked Image]
But at a price that may make a custom aluminum tank price reasonable.
I think you have to have a serious weight savings Reason
Or a Passion ...to go the composite route

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If you have an original (no matter what state it is in) make a mold of it. You only need any bath, tub, box, whatever, full of plaster.

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ducati endurance racer

https://www.flickr.com/photos/scurvyknaves/8393434173

love these grp tank, with fuel gauge


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Originally Posted by koan58
If you have an original (no matter what state it is in) make a mold of it. You only need any bath, tub, box, whatever, full of plaster.

I'm going to do that with my OIF export tank before I paint it.
Judging by the prices being demanded for some very dodgy used ones I believe that it might be prudent.

Come to think about it, I don't see why I shouldn't make a set of female GRP moulds direct from a prepared metal tank ?

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Originally Posted by ferretjuggler
Thanks for that.
I did a bit of Googling myself and learned that you're supposed to carve out a replica of the shape you want from Green Floral Foam.
Yes they do sell it on eBay but only in house brick sized lumps its going to take about £20-30 worth all glued together for a decent size tank.
After that it's a case of making a pair of female moulds around it.
Exactly how to split the moulds and how to join together the two tank halves seems to be shrouded in mystery.
Loads of issues with resin types that are fuel resistant and ethanol is the villain of the piece as usual.
I see that BSA soon returned to steel tanks after a couple of years of GRP.
I wonder if this was due to practical issues or done on the advice of the lawyers ?

It has occurred to me that it might be a useful way to get a spare export tank for my OIF A65.
I've got a rough original that will filler and paint up OK.
But I've always been told that these tanks have a terrible reputation for splitting.
I really wouldn't want to pay £300 for an Indian made tank just to find out that it's true.


Once you lay up the fiberglass matte and resin over your green floral foam, and roll out the bubbles, there is a whole tank, one piece with your filler cap also bonded in during this process. Then once you have the petcock areas reinforced with a steel plate, also embedded into the fiberglass bottom, you can let the whole thing cure. Once that is done, you dissolve the green foam with a solvent and pour out mess and rinse well. I can't remember which solvent, but you can use alcohol, or some type of solvent that leaves no residue, test it on the left over foam. Your tank is now one piece, and no worry about bonding top and bottom together. shape, sand, and give it a protective coat in the tank! Gel coat the inside and outside, prime and paint...
Charlie


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