Use What You've Got - Kawasaki GPz1100 Cafe Bitsa

Bevelheadmhr

Coast to Coast
DTT BOTM WINNER
My mate Jeff decided to use some of the junk.. er valuable old spares ,.. he has to build a café bike. I got involved as he knew that I too had some 'valuable old spares' that I could donate to the build.


The 80's Gpz1100 Unitrack wasn't an ideal start to the project. For reasons lost to history, its engine mounts had been cut off, along with the entire back end, including the shock mount. The original engine was still present, but had no internals, it had no carbs, no exhaust, no wheels, no front end, no electrics, no bodywork. Still, got to use what you've got, and that's what we did.


So what did we have?


We'll start with a Kawasaki ZXR750 swing arm and shock, so that can be made to fit the frame. Next a dented Zephyr 1100 tank would need some work to fit the frame, but it'd look pretty good.. so on it went. For the front end, the original plan was to use a pair of ZXR USD forks in one off home made billet yokes, but they turned out to be way too short, so something else would have to be found.


But before all that, new engine mounts would need to be fabricated and welded to the frame, along with alloy engine plates.
That's where we are up to, having only made a start last week.

Since I'm making new rearsets for my Norley, the original pegs and levers I used (made by the German company LSL), while being too modern in design for my bike, will look fine on the Gpz1100. Though of course they'll need work to fit the frame.


The ZXR750 shock will be mounted to the strengthened frame via a pair of brackets to be machined from 1/2 inch alloy plate.


While the seat unit (still to be decided upon), will be mounted to a sub frame which will be bolted to the back of the frame. This is to make changing the back end much easier in future... changing the seat height or seat unit itself. We did try the Rickman seat unit from one of my old projects, which looked good, but it was wider than the rear of the tank, and would need too much work to make it worthwhile to use.


Its also having a few cool parts that are cast offs from other bikes.. such as the billet clutch cover spacer... used to give space for a lock up clutch.
 

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Here are the LSL foot controls I donated from my Norley, with some 8mm alloy plate beneath which we'll use to make their more appropriate replacements..
 

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The ZXR750 USD forks we were planning to use, proved to be way too short (3 inches) for this frame, so a pair of early ZX6R forks were pressed into service instead. These are still too short, but only by about 1 1/2 inches. So the stanchions are going to be lengthened by welding on the end piece from another bent pair of the same stanchions. Well, that's the theory anyway.


While work on a outrigger bearing, to support the gearbox sprocket continues. Got no pics, but I have got a video of progress this week..

https://youtu.be/yXTE0yiZ7VY
 
Very cool. I'm onboard for this one. I love old Kawi's. Also, I've never seen anybody lengthen fork tubes, should be interesting.
 
canyoncarver said:
Very cool. I'm onboard for this one. I love old Kawi's. Also, I've never seen anybody lengthen fork tubes, should be interesting.
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I'm subscribed, interesting project!

It will be cool to see how the fork extension works out, might help out a lot of guys who put newer forks on older bikes. That is a nice looking gas tank too.
 
I'll try and film the work to forks, wont be for a week or two, as we're currently busy making a set of billet conrods for another Kawasaki project.
 
Its possible to extend some forks internally. I went to dig up the thread for you on it but the guy deleted his photo bucket account. heres how he described it anyway....

Decided i could use a bit of extra length on the front end
So had a bit of a measure and discovered that the ZX10's forks fixed top bush is 160mm from the top of the fork outer leg .
And the fork slider has a full 34 mm of unused surface above this in an uncompressed state . So i figured there's a safe 32mm of extra length i can gain without too much trouble and even less expense :D
Just a matter of extending the damper assembly (which controls fork travel) by 32mm.
A bit of a rummage turned up some old ally ZXR fork tops
And a couple of gixer srad swingarm bearing spacers which were perfect donor material for the job
A combination of turned down zxr adjuster pressed into a srad spacer
Produced the extended spring preload spacers
Next turn up the threaded damper rod extensions
On which i milled some flats
To take a spanner
Then add some longer preload rods (more donor zxr)
And screw it all together
And there you go :)
 
I think the issue with modifying the forks as suggested in the link, is that its closing the gap between the bushes, which isn't a good idea. Also in this case it wouldn't give the extra length needed.

This week work has progressed ok, with various areas being worked on. Since I filmed it all, no point me writing about it, as you can see it here


https://youtu.be/TxThjqb1_dI
 
Would the machining be too expensive to have longer fork caps built? Using the same amount of threaded portion and then a longer (lets say 1") portion the same diameter as the fork tube and then the nut portion above it, would this be feasible?
 
CrabsAndCylinders said:
Would the machining be too expensive to have longer fork caps built? Using the same amount of threaded portion and then a longer (lets say 1") portion the same diameter as the fork tube and then the nut portion above it, would this be feasible?


That would work, though you'd need more machining to add the threads etc. Used to be popular in the 70's to extend forks for chops.. we called them slugs, and were generally frowned upon, as they make the fork weaker.
 
There are some people that build them.

There will never be a set come out of my machines.

That added length is what the triple is going to be bolted to. To much risk there, imo.

1" isn't going to weaken the forks, really, you'll just be clamped to the weak point.
 
There are Pluses and minuses of each approach, I'd favour a stepped top yoke, but that's a lot of machining and cost. We'll see how this option pans out.
 
In the meantime, here's a pic of the rear shock mount almost finished..
 

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Made the stainless exhaust stubs and alloy collars (which still needed a bit more work in this pic) which is the start of the exhaust system..
 

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