A Down Under tribute to Anthony Gobert!
Say hello to a Zx-9r-powered 1993 Kawasaki ZXR750R M1… this is one special track bike inspired by one special talent called Anthony Gobert.
Heath Griffin has always had a soft spot for FIM spec 750 World Superbike era machines as well as 500cc GP era bikes and the legends that rode those bikes. A 500cc GP V4 is really out of reach for most, however, with some bargaining and a lot of hard work, a bike that replicates the era of our own Anthony Gobert, Akira Yanagawa, Scott Russell and your own Terry Rymer has been created by this Aussie track day and road racing addict. The 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 see now. We will let Heath take up the story. I mentioned to a mate Jon that I would be after a bike when I arrived home and 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, limitededition World Superbike homologation model was my daily work hack: hell, life can be good at times! Anyway the Kwaka must have taken exception to this sort of disrespectful treatment and 12 months down the track it decided to throw the number two con-rod out through the crankcase. I started searching for a bargain replacement motor and somehow got side-tracked onto some interesting ZXR websites. A ZX-9R motor looked like a pretty straightforward swap. These motors were available for less than the price of a replacement 750 motor and as Colin Edwards (another WSB legend) once said: “There’s no replacement for displacement.” So in goes the ZX-9R motor, back on the road, problem solved and 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 this day a few things became apparent. Firstly 1993 model brakes and suspension are severely deficient on track. Issue number two was that I was never going to be prepared to push anywhere near the limit with those mint ultra-rare road fairings and priceless alloy tank on the bike. I soon decided that the ZXR was to become a track day only machine.
First on the agenda was front suspension and brakes, as these were causing me the biggest issues with track performance. At first I was looking at building an authentic Anthony Gobert replica, however after seeing the heart-stopping prices being asked for that-era Ohlins forks and AP six-pot calipers I decided to forego some authenticity and head for performance and fun at all costs! I decided on a Yamaha R6 front end, as the WSB ZXRS of the era ran five-spoke rims and the late model Yamaha brakes have an excellent reputation. As it turned out using all Yamaha parts was going to be the simplest front-end solution, so 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. With the stock swingarm out of the bike some colour co-ordination issues were again on the agenda, with the stock ZXR-R frame being light grey, and the ZX-10R swingarm being black. I have always been fond of the brushed alloy look, so out came the paint stripper and Scotch-brite pads. Many painful hours later and a brushed alloy frame and swingarm were the results. Now to fitment, and once the tape measure came out it became apparent that this mixture of parts was going to require some serious massaging to get everything to fit together! For a start 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
“With a ZX-9R motor, the flatslides, Akrapovic and the rest, 150-160bhp could be achievable with ram-air. The bike also handles fantastically!”
being owner of a precision CNC machining company (Russell Symes & Company in Hornsby Heights) started to come in handy. For reasons I still cannot fathom I decided that modifying the swingarm would be the best option (wrong) and so onto the machining centre it went. Now along with the problem of fitting the R1 wheel, the 2004-2005 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. With all of the machine work done, everything was bolted together and we were back to Oran Park for some testing. The final part of the chassis build was to find a decent rear shock. Despite numerous emails to a certain favourite Swedish manufacturer, 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 at a very reasonable price. Coupled with a 2005 Kawasaki ZX636 linkage, and a small mod to increase the rear ride height, this shock was a perfect fit. With the chassis and suspension sorted it was time to look at the bodywork for some extra peace of mind at the track. Firstly I managed to source a
full set of ex TKA (Team Kawasaki Australia) carbon-fibre fairings, including a CF petrol tank, alloy sub-frame, and an ex Troy Bayliss torque-arm. 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 web trawling and three different paint suppliers I couldn’t get anyone to supply me the right colour. After spending two hours in the fourth paint shop and with the colour matcher telling me that I’d really be better off going somewhere else, I made him 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. I bought a spray gun and had a go (well a couple actually) and I’m pretty happy with the result. It’s no 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. With the rest of the bike pretty much complete I now turned my attention to the stock ZX-9R motor. 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 air-box, 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 superlight. 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. With the intake side of the power equation sorted I managed to find a brand new Akrapovic Race system for a ZX-9R, which (although not a Muzzy system like the original carried) is more suited to the ZX-9R motor. 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. 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 near 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. The current dyno figure is 136.5bhp at the rear wheel, without ram-air, so with these mods 150-160hp should be readily achievable. 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. 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. 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 as a whole handles fantastically. I love it!