A Tale of Two Zeds

A few months ago a friend, a bike mechanic, started a project for a customer, the aim of which was to restomod an old late 70's Kawasaki Z650. The end result wasn't to build a bike with the latest tech, but to build a bike as if its from the 90's. The owner has owned the bike for more than 35 years, and so is very attached to it. Over the years the old Zed had gained a different engine, from a more powerful GPz750, along with some cool upgrades from the 80's. Everything except the frame and bodywork was to be changed.

The bike hasn't been run since 2000, so the GPz750 was sold off, and another engine used in its place. This new engine came out of the iconic GPz750 Turbo, but the engine was rebuilt with 810cc forged pistons and a bigger turbo, which is now good for over 150bhp, how much over depending on the boost.

What about the second Zed of the title?

Well, the old 750 engine, which hadn't been run for more than 24 years, was bought by an idiot.. me !

As it would be needed for my own project for 2024.

In early January, I bought a frame for a 78 Z650, which most importantly had its logbook/V5, something that's needed in the UK to allow a bike to be used on the road.

I didn't buy a complete bike, as last year I had restored a similar 650 back to (almost) standard, so this new project would be very non standard, with everything being changed, there was no point buying a complete bike. At the time the only other part I had for the project was a swing arm from a ZXR1100..

Since these two bikes are being built at the same time and both are the same model, with only a year difference in age, they should make an interesting build thread.

I am behind compared to the turbo bike, as that arrived at my friends workshop with the turbo engine already built by another workshop, so all my friend had to do was install it into the modified frame... or so we thought.

The owner of the turbo saw one of my other project which was a ZRX1200 swing arm, he liked it, so his bike soon gained the same arm. Those swingarms don't fit as standard, they have to be narrowed to fit the old frame.

Stainless engine bolts were made for both bikes, along with thick 10mm alloy engine brackets. The GPz engines have slightly different engine mounts compared to the original 650 engine, therefore spacers were machined to make everything work as it should. The engine is solidly mounted into the frame now, with the rubber mounting on the front of the engine eliminated.

With some bracing the frame was powder coated and the new turbo engine bolted into place..

Meanwhile in January my own project got off to a slow start as I spend hours on Ebay hunting down all the many parts I'd need for my own build. With a good tank being particularly difficult to source. But some damage to the alloy ZRX1100 swing arm was repaired, and some welding was done on the frame, to add various tabs, and remove unwanted brackets etc. Then the frame and arm were sent off to be powder coated, both gloss black.

Before my ZRX swing arm went away for powder coating, stainless top hat spacers were machined, so that the bigger ZRX bearings would work with the 16mm swing arm pivot bolt. The latter was another homemade part, in stainless too.

Back to the turbo, a problem was found with the engine, a big problem. Turning over the crank by hand, didn't result in the transmission turning.. not good. With the engine removed from the frame and the sump removed, the reason became clear. The transmission input shaft is turned via a hyvo chain from the crank. This hyvo chain was new, but too big. Turns out all the 650/750 engines use a 62 tooth hyvo chain, except the turbo, which using a 60 tooth chain. The engine builder had incorrectly fitted the wrong, longer chain, which couldn't engine with the crank. They must have known they'd got it wrong, yet didn't bother to correct the issue. We suspect because they knew they'd be closing the business soon, so wouldn't be around the problem was found. They charged the poor customer over £4000.

To fit the correct hyvo chain the cases had to be split, and the crank removed, then the engine reassembled.

The turbo owner wanted to create the bike he'd always wanted back in the 90's, when he could never afford it. Therefore the forks, brakes and wheels are from a Kawasaki ZX7R of the era, but all rebuild and restored of course. The forks are shorter than they need to be, therefore thick billet yokes were made, which suits the look that's wanted, and also allows the forks legs to be dropped and so give more ride height. The resulting gap as you look down on the top yoke is filled with machined spacers which still allow access to the preload adjusters.

For my own bike, the goal was to make it as light as possible, while increasing power, and fitting modern suspension and brakes, all to be done on a sensible budget and completed in a year.

The original Z650 as standard made around 62 bhp at the crank, and weighed a hefty 510 lbs with mag wheels, but only 485lbs when fitted with the lighter wire wheels and drum rear brake. My target is to up the power to over 80bhp and to reduce the weight down to 400lbs dry. This will make it considerably faster than Kawasaki's own new model the Z650RS.

The lighter alloy ZRX swing arm is a good start, as is removing the heavy centre stand and its mounts on the frame. Next the heavy chrome rear fender and rear lamp (which I didn't have anyway) were replaced by a simple stainless splash guard and mounting a ZX6R rear lamp tucked under the tail piece. The latter being an excellent aftermarket part in ABS.

Having finally found a decent tank, though it does have a couple of small dents, the bikes bodywork is slowly coming to together, while a rare Giuliari seat was fitted, swapped from my other 650.

The R6 fork legs were painted black from silver, while the yokes were not such an easy task. Some welding and machining were needed to fit a Kawasaki Zed stem into the R6 yoke. The top yoke also needed work to fit risers in place of the OE clip ons. A front fender from a XJR1300 looks good, but its mounts are slightly different from that of the R6 forks.. more work needed.

Work needed, yeah, but you are certainly up to the task. Looking good.

Made a start on the headlight. indicator and dash mount. Started by making a template.. then making it in 5mm stainless bar..

Progress should speed up soon, as just rented a small workshop on a local farm, its very cheap, but has no power. But its mainly going to be used for storage so I have room to work back home. The owner tells me the deeds of the farm show it was built in 1777..

Test fit of the R6 wheels before they go off to be coated, while gauge bracket done and now also needs to be ceracoated. Next need to make brackets for mounting the headlight.