Kz1000 Carbon Fiber Fuel Tank

Thanks for your input otakar. Based on the rather complex curves already present in the tank, I feel confident the composite replica of the tank underside without the ribs will be stiffer than steel unit with them. If one of my sidecovers can support my 200lbs of dead weight, I think the tank components will be equally rigid and strong....if not more so. The good news it that it's only plastic and easy to remove if I find I need those ribs in the composite part. I have not, however, heard anything on the tank design and its mitigation of harmonic vibrations to reduce fuel agitation. That sounds like interesting reading, could you point me in that direction? I certinly don't want a little fuel with my foam :laugh: Thanks

I suppose fuel tank design is not a topic that comes up often, so subjects like this are seldom discussed.

I just remember a company making composite tanks back in the late 70s and there being serious foaming problems. They wound up curing the problem by making the walls something like 1/4" thick. I also remember that when the early ones came out that the cure was to stuff the tank full of those Mesh dishwashing scrubby things. Sort of like those synthetic Luffa Sponges are today. Made out of some kind of nylon material. This is only stuff that I remember from my old racing days.

I did this one out of composite Kevlar/Graphite/Glass last year.

Her's another angle.

I wonder if an internal baffle would accomplish the same thing...... I also wonder if the harmonic vibration had anything to do with the materials used. You did a fantastic job on your fairing. Did you hand form it, or use a mold? How many layers of each type of fabric did you use, what order did you lay them and why? Did you use polyester, vinyl ester or epoxy resin? Sorry, that's alot of questions!

I have had a fiberglass tank on my bike for years now. No issues with fuel foaming, tunnel is smooth and glass is about ¼” thick, tank is rubber mounted. Road racers put fuel cell baffling (pieces the size of a big sponge) in their tanks to prevent fuel sloshing effect when flicking side to side and braking and accelerating really hard, it affects weight transfer and thus handling. Not something that's really needed on the street for most people. This baffling material is an open cell foam that has a slow release rate so it does slow down fuel evacuation in case of a crash where the tank is split open.

Never been questioned by the cops about what material the tank is made of and my bike is far from inconspicuous. Most cops here leave vintage bikes alone unless you're speeding or riding like an a*hole. I don't know of any laws that make it illegal for street use. My tank is well constructed and solidly mounted. I understand and accept the risks of riding (crashing) with a fiberglass tank rather than a steel one.

Modern pump gas is crap especially ethanol kills fiberglass tanks. Vinylester is commonly used for tanks and stands up to (non-ethanol) race fuel plus most race tanks are drained between races. You will really need to coat your tank with an ethanol resistant epoxy in order to use pump gas.

Thanks dutchz, I think you're the first composite tank owner I've heard to chime in :laugh: I had planned to line the tank as you suggested. I still haven't figured out the laminate section........ any thoughts? I was thinking (from the outside in) 2 layers of carbon, 2 layers of kevlar, 2mm coremat then 2 more layers of carbon. That should yeild a VERY stront cross section since it's almost double what I use on the sidecovers. I have the sidecovers at 4 layers, with 2 of them being fiberglass and the coremat. We'll see, won't we?

otakar wrote:

Her's another angle.

It looks great cut and buffed otakar, but do you have any pics during layup? It's hard to see the composite construction under all that shiny paint :woohoo:

After I sanded down the first coat of body filler on the underside of the tank, I test fit it on the bike just to make sure I didn't fill anything that was important for clearance. Everything looked good (thank god I used curved center tube to perimeter tube braces though :blink: ) so I decided to start removing the rear tank hold down and the front mounts. I don't know how many of you guys have actually paid attention to the construction of the stock tank, but that rear hold down tang is held on by 6 spot welds :ohmy: There was barely enough room to cut them all out and leave some steel behind

The front mounts only have 4 spot welds each, but I need to swing by my favorite chinese tool supply store and get a pnuematic right angled drill. It's tight quarters for my regular hand drill....too tight :pinch:
I need to spread another lift of body filler on the underside to fill in the low spots, and finish the dents on the top of the tank. I was thinking about the tank filler, and how I would not only cover the hole, but find centerline of the hole. I think I've got it figured out though. You'll see soon!

Something to take into consideration before you cut the seam off of that tank. I have seperated one of these tanks before, and the top half becomes quite flimsy once seperated from the bottom. So you might consider taking your mold of the top before you cut them apart. Or match mark the two halves so that you can brace the top to properly align to the bottom. It will try to taco and twist once the support is gone. I would hate to see you get a mold of the two seperate pieces and have the parts not properly line up when you went to assemble the carbon tank.

Don't worry Josh, I'm not taking the tank apart. I'm only taking the tank mounts off, as they will interfere with the bottom mold. I bet the tank was flimsy once it was disected! I gotta say, Ma Kaw didn't want the mounts comming off too easy :laugh:

Good, I figured that you didn't need to take it apart, but I saw all of that drilling going on. I thought I should warn you in case that you were planning on splitting it. The tank that I cut was in really bad shape with major rust and it has one of those dents in the top where the metal is very stretched. I don't see how it could be fixed without taking some pie cuts out of the steel and welding it back up. Not worth the trouble in my opinion. I got the replacement off ebay for less than $100. I'm sure that you know some bodyman tricks. Anyway, you have to stretch the top half fairly hard to even get it over the bottom anymore.