Kawasaki Z650 Seventies Special


Coast to Coast
I need another project like a hole in the head, but I was offered the basics (very basic) start of a project as part of a swap, and since it was an old Kawasaki inline 4, with a deep breath I took it on board. This will be my 2020 project, though parts may be bought and made in the meantime.

I have a pretty clear idea of what I want to build, those details will have to wait, but what I have is a 1978 Kawasaki Z650 frame, a Z1000 tank and various parts that may or may not end up on the finished bike.

If you've checked out the pic below already, you'll have noticed the frame isn't quite as it left the factory. Its been butchered like some poor animal.

There's a good reason for this butchery, as the frame needs to be widened by about an inch (25mm) to accommodate a GPz1100 motor. Well, I say Gpz1100, but I suspect when we've finished with it it'll be a bigger than 1100cc. It may even get a supercharger, not sure yet. It'll be having better suspension, but not USD forks. As for the wheels, 17inch 3 spoke wheels would be cheap and easy to find, but I prefer 18inch spoked wheels.. pity I don't have any. I'll need to find a suitable pair of hubs first, then I can build and true them myself.

Updates will be slow at first, as I have other bikes to finish, but I hope to have it on the road by the summer of 2020.. famous last words :)


  • Z650part1 019.JPG
    Z650part1 019.JPG
    808.1 KB · Views: 492
The Z650 frame didn't have a swing arm, and even if it did, once the frame has been widened it wouldn't fit anyway. A different swingarm was needed. From our pile of junk.. er .. valuable old spares.. we found an old steel arm taken from a 90's Kawasaki ZXR750. But ZXR750's were monoshocked, while the Z650 is and will remain twin shocked. Oh and it was also at least 100mm too long. Not a promising start.

However, in the workshop I found a pair of 'spare' one off alloy wheel adjuster blocks.. which I soon snagged for the Zed project. Next I chopped the swing arm down to size by cutting off its original wheel adjusters, in preparation for fitting the new adjuster blocks. To do that will need a jig making to ensure the finished arm is straight and true when its all welded together. That may be a few weeks away, but then I don't want to spend too much time or money at the moment, as the Zed is supposed to be my 2020 project. The mounting bracket for the mono shock will have to be cut off and new shock mounts made and welded on to take twin shocks too.

In the photo you can see that the new alloy adjuster blocks are far too wide for the swingarm, but that's ok, as the extra will be needed when we add an under brace to the arm. I could've jus gone out and bought something from Ebay that will fit easily, but where's the fun in that :p


  • swingarm2 008.JPG
    swingarm2 008.JPG
    1.2 MB · Views: 451
  • swingarm2 007.JPG
    swingarm2 007.JPG
    5.9 MB · Views: 461
Hope so. its not about the destination but the journey to get there as they say.. Looks like I'll be using a set of 73.5mm pistons as they are a bargain.. that will take the 1100 engine out to 1170cc. nothing too radical, but should make a good road engine.
The bike now has a set of GPz cases which have already been bored out to take a big bore kit, though that wont be needed with the modest 1170cc pistons I plan to use. It also has a barrel, with a badly scored liner in one of the cylinders. Which shouldn't be a problem as the cylinders will need to be taken out by 1mm, which (fingers crossed) should remove the damage.

Placing the cases in the Z650 frame shows the front engine mounts are way off, not really a surprise. Rather than cutting off he original mounts and welding on new ones, I think it'll be easier just to cut off the lower frame rails completely and make new ones.

Boring out the cylinders will cost about £80, which will be the first money I'll have to spend so far, as everything else has been free or been a swap. No doubt by the time its finished, £80 will be a drop in the ocean. This is supposed to be next years project, or so I tell myself, but it hard to resist working on it now.


  • NorleycarstartandJeffvlog 014.JPG
    NorleycarstartandJeffvlog 014.JPG
    2.3 MB · Views: 453
The one off billet wheels and front end from my old drag bike may be used on the Z650/1100, while parts for the engine are coming together. All is explained here..

Not had any time recently to work on the bikes, but this week I was given a swingarm taken off a fire damaged ZRX1200. Its covered in melted plastic, but apart from a small dent in one of the braces, its all good. I'll get the dent sorted by alloy welding it and then bead blast it to hopefully remove the melted plastic.

I'll also remove a few brackets and it should be ok to use on the Z650/1100 project. Oh and the eccentric wheel adjusters were a bit scratched, so cleaned them up on the lathe. They'll need to be re-anodised, but that can wait.


  • Z650SARMadjusters1 007.JPG
    Z650SARMadjusters1 007.JPG
    1.6 MB · Views: 414
  • ZRX018.JPG
    2.6 MB · Views: 409
Got the damage to the ZRX swingarm fixed by having it ally welded, then took it to a friends workshop to use his bead blaster to remove the melted plastic that covered it. Turned out ok, I'll have it powder coated but only when the frame is also ready for powder coat, which wont be until the dry built is complete.

You can see the process here..

This project is supposed to be my 2020 project, but couldn't resist doing a bit of work on it now. Recently the ZXR1200 swingarm has been mated with the billet rear wheel and a Brembo caliper mounted on a one off alloy mount.

Also made a start on widening the Z650 frame to accommodate the bigger Gpz1100, by mounting the frame (or what's left of it) on the home made frame jig..



  • vlog21a 011 (2).JPG
    vlog21a 011 (2).JPG
    1.2 MB · Views: 375
WOW the vids are friggin awesome fun to watch!!! 8)

One question, Is this bike going on the street or is it being built for the track?
Its going to be a street bike. I usually know beforehand how I want a build to look before I start, but with this one I'm still open minded. It may even be supercharged, we'll see.
Will do, the frame should be welded back together by the end of the week, then I can play around and see how it looks with the ZRX swingarm and billet wheels loosely attached. Progress tends to go in fits and starts, as time and money allows. BTW there are a lot of build videos on the YT channel, so if your bored they could keep you occupied for many hours.

In the meantime, I've been trying to get all the wiring working on this old thing..


  • MHRPart2a 004 (2).JPG
    MHRPart2a 004 (2).JPG
    2 MB · Views: 372
Having a frame jig that tilts helps a lot when welding... and for tea breaks :)

The welds look rough at the moment, but they'll be linished and cleaned up when the engine is out of the way. The old Z650 frame now has a reinforced swingarm pivot area, with the spindle increased in size to 20mm to suite the ZRX swing arm it'll be using. The frame will also have additional bracing on the front down tubes and underneath the gearbox.


  • Z650Part7a 004.JPG
    Z650Part7a 004.JPG
    1.8 MB · Views: 355
  • Z650Parta7 007.JPG
    Z650Parta7 007.JPG
    1.7 MB · Views: 356
Top Bottom