Don Qixote would be soooooo proud of this next lil' joust with an imaginary enemy.
I'm afraid this is going to generate some fairly....er....visceral reactions, so I'll give you a lil' time to gird your loins before I get into it.....
It's weird, but in all the hallowed annals of gravitational theory, Newton, Einstein and co never once mentioned carbon fibre....they obviously never owned a Ducati. It seems to be the natural order of things: the tides are drawn to the moon, Ducati owners gravitate to carbon fibre.
I’m not really into cosmetic carbon, but some of the associated weight savings can be quite attractive. Replacing ABS plastic with carbon is a bit "Meh...": it’s a lot of coin to not save an equivalent amount of weight, right?
But, replacing heavy steel with carbon fibre? Now that is a very pretty proposition. That steel fuel tank weighs a motza, a carbon tank weighs a fraction of that....but unfortunately is priced at an inverse ratio to weight = big $$$.
Ok, are you fully girded? 'Cos from here on you’ll be confronted by someone on the LH side of the intelligence bell-curve, armed with nothing but enthusiasm and ignorance:
How to make a carbon fibre tank for cheap?
Unfortunately in my phone trashing incident mentioned previously I lost a swag of photo’s, but realistically you’ll want to avert your eyes anyway, so no harm done.
I had a couple of random thoughts providing motivation:
- why make an 18L tank when my trackday sessions are only 15min and club races are just 6-8 laps?
- anti-slosh foam works a treat, but why treat the symptoms (3-4L sloshing around in a 18L tank) when you could treat the cause?
So I set about making a carbon tank cover to go over a small sub-tank.
I had a beat up steel 749R tank on hand, but I had to make it aesthetically presentable before I could take a mould from it…and I had to fill in that god-awful tank pad recess:
This is the eventual result:
We’ve barely started and this is where things go pear shaped: through my aforementioned ignorance, combined with a healthy dose of stupidity, I fucked up the mould. Truthfully, I didn’t really expect this to get much of a result: the complex shape of the tank makes it a nightmare to pick some split lines that will allow a mould to be removed without mechanically locking onto the tank. Even the narrow knee recess section flares out slightly where it meets the seat. So the best option I could see was a simple 2 piece mould split straight down the middle and then rely on enough flex in the fibreglass to sneak it past the rear corners.
Bottom line: I should have taken the time for a 2 hour round trip to my local fibreglass materials supplier and picked up more suitable materials. If I’d had a bit more confidence in the process I would have achieved a much better result, with a lot less work, in a shorter time...note to self!
I did end up with a usable mould, but even working with a "slow" epoxy hardener it wasn't easy working with such a complex shape and fibreglass matting that was a tad too heavy/stiff to easily follow the contours:
The end result, along with looking like something from the Pleistocene era, had a heap of pinholes and small voids, which I patched with thickened epoxy. Turns out it's a bloody nightmare trying to sand a concave surface. especially with such hard material (cheaper polyester is softer, and ordinary filler/bondo even softer again). I'd initially spent a fair bit of effort shaping the groove into the now tank-padless OEM tank, but I wasn't happy with the way it transferred onto the mould so I decided to just remove it all together = more sanding. Then I had the idea of painting the inside of the mould and working with that as a softer surface.
The term “epic fail” come to mind, as the paint, despite a gazillion layers of mould release agent, came away with the carbon cover. It’s not like the paint didn’t stick to the mould (it had far more stickability than the average millenial), no, it was just that like that person you desperately need to see at the city council, the "release" component in release agent decided to take the day off just when I needed it most. The thing was just an absolute bastard to separate, and would have had anyone watching rolling around in stitches much the same way I was rolling around grappling with something I just couldn't get a fingerhold on.
And again, wet lay carbon fibre was a painful exercise on such a large complex shape in the time available before the epoxy went off, even with the slow hardener and pre-prepared carbon panels roughly cut to to suit each plane.
Hence the patchy red "I have a skin disease" result, seen here as I start trying to make it presentable:
It won’t win any concours prizes (they wouldn’t even let me in the gate!) but it only weighs 0.56kg and will paint up ok. After a clusterfuck of those proportions we’ve reached the “bingo fuel” moment: too late to turn back now.
So this is what I had in mind with the tank cover and sub-tank:
Aaaand, looking at the above pic's, the only thing obvious is that I've completely failed to capture the relative proportions.
So the carbon sub-tank, a bargain-buy carbon Suzuki RMZ450 unit, is 6.2L where the OEM 749R tank is 18.3L. FYI, the 749R tank is 749R specific, the generic 749/999 (even the 999R) unit is just 15.5L giving slightly different (better, if I'm honest) aesthetics and much reduced range. Why? World Supersport rules stipulate an OEM tank. No such rule applies to WSBK so the Corse/RS WSBK tank is vastly different.
It sounds simple, and probably is for someone on the other end of the intelligence bell curve, but it took me a while to find something that would accommodate the OEM fuel pump setup:
Keeping the RMZ pump was considered, but ultimately I wasn't confident it could reliably supply 170hp worth of go-juice, so I had to sort some way of mounting the 749R fuel pump assembly:
Carbon fibre raw materials aren't too expensive, but any decent thickness of manufactured carbon plate is drug money. So I basically "squeegeed" about 30 layers of carbon fibre/epoxy together, creating a thick carbon block, spun it up on the lathe, bonded in the fixings to make something resembling the OEM tank pump flange, then bonded that in place on the RMZ tank:
A quick polish of the internal surface to give the pump base O-ring a smooth sealing surface and a trial fit has me feeling cautiously optimistic:
I had to "cut 'n shut" the square end (-20mm) to position it within the cover and I fitted a spare filler I had, basically sandwiching the cover (with a gasket) between the filler and tank:
This gives a better appreciation of the relative size of cover vs sub-tank:
Aaaaaand here we go again, completely cocking up the perspective, but it gives you some idea (note: I machined a knurled aluminium rear mounting bolt to suit, so no tools required:
Me being me, it turns out I also cocked up something else:
The bulge in the belly of the sub-tank is clashing with the vertical throttle body bell-mouth so the tank sits way high at the front: Lord give me strength....or at least beer, yup, just beer will be fine.
Bloody hell, I feel like Alice in Wonderland going further and further down the rabbit hole......
With the gears of inspiration sufficiently lubricated, my solution was to epoxy a couple of layers of carbon fibre around a cling-wrapped cardboard shipping tube:
To make a carbon fibre half-tube section:
Then removed the belly-fat from the sub-tank and bonded in the tube section = mechanical liposuction:
FYI, the fuel pump aperture gives good access so I've internally filleted the tube-section in place with an epoxy/chopped strand carbon fibre mix.
And it looks like Alice got outta jail:
The above has the front of the tank resting on the frame rails so it will actually sit 10-15mm higher again.
Hmmm, we're getting to the pointy end now, but I really need to stabilise/support the rear of the sub-tank. Smaller volume or not, it just didn't seem adequate to have the whole thing hanging from the filler neck/cap arrangement.
I umm’d and aah’d for a bit, weighing up various configurations but eventually decided to make use of the mounting nuts already cast into the sub-tank. I knocked up an alloy prototype for a rear mounting “strap” then used that as a mould/template to make a carbon over kevlar version:
2 x layers of kevlar + 3 x layers of cf makes the strap fairly stiff, with just a bit of flex to cope with any vibration issues.
Tank secured with low profile Ti bolts...:
....positioned under the recess fabricated into the RS carbon seat:
The carbon RS tail has been hanging on my shed wall for +2 years, and even allowing for looking through celebratory beer goggles I'm quietly chuffed: it actually looks like a bike now....a very ugly bike, but a bike none the less:
But in the back of my mind, amongst the tumbleweeds and mental belly-button fluff was a sarcastic lil' voice: "Goodonya champ....but what was the bloody point?!"
So with a deep breath I popped the completed tank assembly on the scales, which I read through squinty “I'm not sure I want to see this....” eyes:
1.47kg, no pump but including filler. Ooooooh, that’s not too bad, comparing well with most store-bought "real" carbon tanks….
….but what does a steel tank weigh?
5.3kg minus pump and filler cap (the filler was fitted to the carbon setup) but it does have a bit of extra filler/bondo added for the tank pad indent and repairs so it probably evens out.
Hmmmm, 3.8kg doesn't sound like much to save but pick up a 1kg bag of sugar...now nearly quadruple that and it's a fair ol' lump of weight.
But it is a lot of faffing around isn’t it? Having said that, it was an interesting exercise, I learned a heap, and it wouldn't take much to turn out a much better version even using the same bunky mould. And I'm hoping the mass reduction has a compounding effect: -3.8kg is nice, centralising the mass is better, and not having 3-4kg sloshing backwards and forwards is better again....the proof will be in the pudding if/when it finally makes it on track.
I guess the elephant in the room is cost, after all there were two drivers for this jaunt down Epoxy Lane: weight and $$$. I looked for quite some time trying to find a 749/999 carbon tank, new units are available but will cost around $3000AUD ($2000USD) landed in Oz. Used are extremely rare and somewhere around $2000AUD ($1500USD) landed. Corse/RS parts are significantly more again, and you need a swag of other parts to even think about fitting one. The bulk of my cost was obviously the used carbon RMZ tank with materials coming in a distant second, but I figure all up would be a round the $800AUD ($600USD) mark.
Still not cheap....and not pretty (yet) but it's a fair stack of cash saved, especially when you consider my long suffering better half may (and who could blame her?) decide to return fire by buying the equivalent amount in shoes!
Initially I wasn't at all confident making a container to safely hold a flammable fluid nestled against my nether regions, hence the re-purposed RMZ tank, but with the screw-ups and work arounds forcing me to attempt things I otherwise wouldn't have, I've got a MKll version in mind that will be prettier, lighter and a lot cheaper. But that's for a rainy day once we're up and running.
