Kawasaki’s 750cc four cylinder racers were the choice of champions and privateers alike in the 1980s through to the 2000s: this replica is a little different…
Kawasaki’s inline four-cylinder 750cc production racers did well worldwide in the various championships they were eligible in. In 1988, with the new global series – the World Superbike Championship – proving to be the perfect way for the major manufacturers to showcase their new machinery, the long-inthe-tooth Kawasaki GPX750 needed replacing.
The first models of the ZXR750 series, the H1 and H2, had motors based closely on the old GPX’S, but thechassis and styling were more in keeping with the competition of the time, most notably the racier homologation specials such as Honda’s V4 RC30 and Yamaha’s OW-01. The Kwak would develop and evolve both on road and track, becoming the ZX-7R from 1996 on.
On track the bike would become the only inline four-cylinder 750 to win the WSB title in 1993 with Scott Russell aboard the Muzzyrun machine but around the world the ‘green meanies’ would do well in all levels of racing, being plentiful, powerful and relatively cheap to run/tune – especially in comparison to the likes of the Ducati V-twin 888/916 family…
We are ‘down under’ and the Antipodean connection to the ZXR/ZX-7 series is an important one. Robbie Phillis campaigned the early versions and the initial ‘factory’ effort was run out of Australia. Riders included race winner Aaron Slight from New Zealand. The Aussie connection carried on even with the likes of Rob Muzzy and his Us-based team becoming the factory Kawasaki entry in WSB from 1993. Slight was team-mate to Russell in his title-winning year, but when the Kiwi went to ride Honda’s new V4 – the RC45– in came youngster Anthony Go bert:awild-riding
Aussie who would appear at the final round at Phillip Island as a replacement for Terry Rymer.
Here’s where Heath Griffin – the creator of this amazing machine – comes in. He’s always had a soft spot for the 750cc WSB machines (and 500cc two-stroke GP bikes too) but building a four-stroke 750 replica of the racers is easier – and cheaper – to do… This bike was bought from a mate after Heath and his wife Angela returned from an extended working holiday around Australia and then it was built to what you seenow.
Heath says: “I mentioned to a mate Jon to keep an eye out for a ZXR750, to which he replied: ‘What about a ZXR750R?’ He then told me that another mate of ours, Mark Dean, had bought one while I was away and was now looking to offload it. I was straight on the phone and a deal was struck. After picking up my new pride and joy it became my daily transport to work and university. That’s right, a ZXR750R M1, limited-edition World Superbike homologation model was my daily work hack! Sadly within a year the bike decided to throw the number two con-rod out through the crankcase.”
Heath then started to look for a replacement motor on the cheap and found that the ZX-9R motor was a pretty straightforward swap – handy as it was cheaper than a 750 M motor…
“So in goes the ZX-9R motor, back on the road, job done. A few months of happy commuting go by, and off we go to Oran Park for a casual friendly track ride day. By the end of the day I realised that the period 1993 brakes/suspension left a lot to be desired and I didn’t want to trash the rare road-going bodywork and alloy tank: time to strip that stuff off and build a track-day only machine.”
Heath set to work: “At first I was looking at building an authentic Anthony Gobert replica, but the pukka Ohlins forks and AP six-pot calipers from that era were too expensive. Instead I’d make the bike perform on a budget.”
The front-end of the machine would effectively be from a Yamaha YZF-R6. “I pressed out the steering stem and turned it down to fit the ZXR inner bearing race, made up a small spacer to account for the slightly longer R6 steering stem, and pressed it all back together with some new tapered roller bearings.
“At this time I also fitted up the R6 master-cylinder with some HEL braided lines and SBS race compound pads. A matching five-spoke R1 rear rim, brake caliper, and master-cylinder were ordered to match. Being a fan of braced-up SBK swingarms (and not having the 4000 Euros for a proper TKR one) I ordered a 2005 model ZX-10R swingarm. These look a bit like a factory swingarm from that very era.”
To get the look right – the ZXR-R frame being light grey and the swingarm being black – Heath set to work with paint stripper and Scotch-brite pads to get a brushed alloy look. He said: “Once the tape measure came out it became apparent that this mixture of parts was going to require some work to fit! The R1 axle is a lot larger than that of the ZX-10R and no bearings were available that would cope with the difference. To deal with this mismatch either a heap of spacers were going to have to be made, or the axle slots and chain adjusters in the ZX-10R swingarm needed to be machined out to fit the R1 axle. It is about now that being owner of a precision CNC machining company - Russell Symes & Company – started to come in handy.”
Heath initially decided to modify the swinger: “I was so wrong, therefore to the machining centre it went. Now along with the problem of fitting the R1 wheel, the 20042005 ZX-10R swingarm is significantly longer than that of the ZXR750R, so I also made up some blocks for the adjustable swingarm pivot to move the pivot position as far forward and up as possible in order to keep the wheelbase to a minimum. My sincere thanks to my friend Max at work who is a fellow bike fan and stayed back late in his own time to help out with some of these machining jobs.”
Heath adds: “The final part of the chassis build was to find a decent rear shock. Despite numerous emails to Ohlins, I was told that a suitable unit couldn’t be supplied. Lucky for me a brand-new old stock WP race shock for a ZX-9R turned up on ebay. Coupled with a 2005 Kawasaki ZX636 linkage, and a small mod to increase the rear ride height, this shock was a perfect fit.”
Bodywork was next – and this had to look ‘right’. “I managed to source a full set of ex TKA (Team Kawasaki Australia) carbon-fibre fairings, including a CF petrol tank, alloy subframe, and an ex Troy Bayliss torque-arm,” explains Heath. “Many hours were spent stripping and patching the bodywork to get a decent base for the new paint job. Next issue was finding the correct tone of green for the job. Despite days of searching, I couldn’t get anyone to supply me the right colour. By the time I got to the fourth paint shop, I made the owner a deal that if he’d give me one chance to mix it myself I’d leave him in peace and pay for the tin no matter the result. Lucky for me the result was good and I left the shop a happy man!”
Heath bought himself a spay gun and did the paint himself – brave man: “It took a couple of goes, but I’m pretty happy with the result. It’s not show bike quality, but certainly good enough for a track bike. To finish off the look I estimated the graphic sizes off old posters and photos of Anthony Gobert and Scott Russell and had the stickers laser cut. With these fitted, along with a ‘Gobert’ reaper on the tailpiece, and some Guy Martin stickers on the belly pan (don’t ask) the aesthetic transformation was complete.”
Now, what to do with that stock ZX-9R motor? Heath says: “I was originally running the 39mm Keihin flat-slides off the 750R motor, however these were in serious need of a rebuild, and therefore gave me the perfect excuse to source some shiny new 41mm flat-slides from the same manufacturer. These also included medium length velocity stacks, and came to me already jetted to suit the 900 motor, with a later dyno run proving they were pretty close to spot-on straight out of the box.
“To house the flat-slides I originally looked at using a genuine WSBK fully enclosed airbox, however some measurements revealed that this wouldn’t fit over the taller 900cc engine, so a custom fabrication was required. This was done by lining the top of the motor and inside of the frame rails with plastic, then filling this with an expanding foam resin to create a mould. From the finished mould I made my first attempt at working with carbon-fibre. The resulting vacuum bagged wet lay-up carbon-fibre air-box certainly won’t win any beauty contests, however it fits perfectly, maximises air-box volume, and is super-light. It is pretty much completely hidden under the tank (which also acts as the air-box lid, like the factory bikes), so the imperfect finish is not really critical. I also moulded up the two air-intake ducts.”
Internal engine mods have been kept minimal. The head has had the ports tidied up and matched to the intake manifolds, the valve seats have been fully blended, and the chambers have been modified as per the KRT manual, but how? Heath adds: “All this was done in my shed with the trusty Dremel. Completing the head work was a light skim on the mill at work to up the compression and installation of the 750R double valve springs. A full rebuild is planned for the future, which will include a Zlock 950cc big-bore kit, a fully freshened up head, some more compression and maybe some velocity porting. I will also be installing the close ratio gearbox out of the 750R motor.”
Other bits and pieces include a Dynatek adjustable ignition system: “The electrics are total loss, with the alternator removed and a custom carbon-fibre battery box positioned in its place,” says Heath. “A working starter motor is retained as I just don’t find it enjoyable to push start motorcycles. A ZX-12R radial clutch master-cylinder helps reduce arm pump with a much lighter pull than stock, and a digital temp gauge rounds out the control mods.” Matched to the motor was a brandnew Akrapovic Race system for a ZX-9R, which – although not a Muzzy system like the original bike used – is more suited to the ZX-9R motor. Heath says: “The current dyno figure is 136.5bhp at the rear wheel, without ram-air, so with these mods 150-160hp should be readily achievable.”
So, Heath, what’s it like to ride? “Well, since completion the bike has been to numerous track days. The rear suspension with the WP shock has been fantastic straight out of the box, with minimal adjustments resulting in excellent grip and tyre life. The front-end is also very good, and the bike on the whole handles fantastically. I love it! And it looks the part, too!”
Squint and it could almost be the real thing...
41mm Keihin flat-slides sport medium-length velocity stacks.
Much machining went into making this work! R6 forks ape Ohlins originals.
Paint was mixed by the owner himself!
Motor good for 130-140bhp.
Brushed ally frame took elbow grease!