Kawasaki GPz600R

Kawasaki GPz600R – The Forgotten Superbike

Kawasaki GPz600RThere are lots of occasions throughout history when the wrong guy is credited with a break through or important event. Certainly while researching this article my recollections of events where challenged constantly. There are lots of references to the GPX 600, both in books and on the web but precious little about the bike that started it all, the GPZ 600. The many history books that cover the Kawasaki marque place great store in the 1984 GPZ 900R as a turning point in motorcycle design, but the real event that has changed the way we look at machines today happened the following year with the launch of the nippy little GPZ600.

This is the bike that sparked exciting middleweight machines ever since. The GPZ re wrote the book on how a little bike should look and go, in the process Kawasaki invented a whole new capacity class, that of the 600 Supersport. Before then the middleweight was set to be around the 550cc mark with many manufacturers producing air-cooled, inline fours, all of similar specification and hence performance, with little or no innovation due to a complacent approach to styling and cautious product placement. Of course we couldn’t have foreseen the crippling cost of modern day Superbike ownership back then. Before then the middleweight class was looked on, certainly in the UK if not the whole world, as a “toy” capacity class, used by blokes to get to work on and some of the LC brigade should they have avoided the car, marriage and two kids trap.

Kawasaki GPz600Kawasaki lit the blue touch paper and away we went, effectively giving the rider exactly what they wanted, following on from the lead given by Yamaha with the RD500LC, they made the whole package more rational and usable, and considerably longer lived. Producing around 73bhp, in a smooth and contained manner, unlike the strokers of the period, the genuine 130mph plus, water cooled GPZ instantly became a hit with the middleweight “boy racer” brigade. The strong engine, which freely revved to 11 thousand, was allied with a great handling chassis with all of the mod cons considered important in those technically heady days of the mid eighties. Sixteen-inch wheels, for quick precise steering, and anti dive forks for when the twin discs where implemented, scored maximum points for the Kawasaki salesmen making the GPZ a literally fly out of the showrooms.

GPz600The machine looked awesome and the finish was very good with Kawasaki’s typically generous application of paint to the substantial plastics. Honda quickly responded with the even more stylish CBR, followed sometime later by Yamaha and their FZR, and the rest as we say is history. The 600 “Supersport” class has been with us ever since and the machines that the breed has spawned always contain technical innovation and performance advancement. As every new season dawns the emphasis would appear to be on that particular capacity for guidance and inspiration, with power outputs well into treble figures these diminutive machines are now very capable and serious motorcycles. It is only the Italians and Americans who have staunchly stayed clear of such machines, even Triumph have recently and successfully I might add, taken up the gauntlet with the TT600 Daytona.

The Achilles heel of the early GPZ would have to be the flimsy steel frame with its detachable down tubes facilitating engine removal. This main loop and the lengthy frame rails to the tail section are easily twisted in all but the lightest of crashes, quite surprising really considering the type of customer intended for the GPZ. The later versions incorporated a much stronger one piece loop and separate rear sub frame enabling that part to be replaced should any damage occur. Running a GPZ now is a compromise due to the lack of suitable rubber although thankfully the companies that do still give us a fitment see fit to continually upgrade their designs with modern compounds.

GPz600RCam shaft problems, due probably to the high, 5000 plus rpm, tick over from cold and lack of a centre stand, causing starvation of oil to the extreme right hand side, were prevalent. Likewise, wear in the Hyvo chain, situated between the lay shaft and crankshaft, is another common and noisy problem.  This gets a double attack of abuse due to it being the drive for the starter motor on to the crank as well. These rattle mostly at tick over as indeed does the clutch basket and anything else if the carbs are out of sync. Carb icing was a major problem and the only cure was to route hot fluid directly from the coolant system around the carburettor venturi and keep the bodies warm. This was at the expense of power but the options were limited and the carb icing could prove lethal if it decided to do its stuff, and completely cut out the motor, at the wrong moment in time.

Sixteen tiny valves are neatly lined up within the narrow head and cam box area, a single cam lobe via a doubled up rocker arm for each cylinder in turn depresses these.  Adjustment is by the vernier method removing the need for trips to dealers in the attempt at getting the tiny shims needed for similar machines. In 1987 the engine was given a larger bore, and shorter stroke, to take the capacity out to 748cc giving us the GPX750. This bike was good enough to run in the top six at WSB level and gave Kawasaki their first world Superbike winner when French rider Adrien Morillas took victory in second race of the 1988 season, the first ever for this newly formed road bike class.

The standard, mild steel, twin silencer exhaust is often long gone replaced by the ubiquitous stainless steel Nexus system, which in turn gives the GPZ a slightly mightier roar with out looking out of place, it does leave the left hand side slightly “lost” in appearance though.

Kawasaki GPz600RWith the seating position placing you firmly in, rather than sat on, you can quickly get to grips with this lightweight machine and feel confident in the cornering ability. Looking around the machine and the small diameter of the wheels give a modern chunky look to the tyres, however the 37mm forks are positively spindly by comparison, they do work well though and provide a positive riding experience even as the pace gets a little hotter. The forks are not adjustable, apart from varying the air pressure a pound or so either side of 9psi, so the designers at Kawasaki must have preformed a great job when developing the bike to have got it so right from the outset and Roger informs me that the GPZ is just as well behaved two up. Although torquey from quite low down I the rev range, power kicks in for real around the 7 thousand mark and continues to pull strongly all the way through to the 11k red line. This gives an effortless approach to riding without the constant up and down the box technique to keep the motor buzzing.

Talking of heat, the engine, with little power below 7 thousand, was quick to get very hot making the idea to fit a cooling fan was a good one. The compactness of the engine, while giving great ground clearance and centre of gravity, does lead to overheating. This in turn leads to the one weak spot that the engine has, the clutch, which, after several runs for the camera, the seven friction plates were starting to give up the ghost. Neutral was increasingly difficult to find when stood still, while up shifts had started to develop that soft “automatic” feel before finally grabbing home.

Kawasaki GPz600RThankfully, brake pad suppliers, like the tyre people, are still providing a good selection of braking material with EBC in particular, still offering a very efficient HH compound. Later models did have an electronic anti dive unit (ESCS) fitted to the forks, this was activated from the brake light switch via a relay under the tank and absorbed no energy from the hydraulic system to activate it. The electronic anti dive worked so well it disappeared from trace never to be seen again. Callipers are the single piston floating type, fitted all around, and these are reasonably trouble free providing the two large pins that the calliper swings on are kept free of corrosion, the pistons can stick but nothing like as often, or as costly to cure, as in similar Japanese designs. These grab a pair of 270mm, heavily drilled steel discs, the relative small diameter of these still give tremendous stopping power due to the relationship with the equally reduced rolling radius of the wheel and tyre.

Controls fall easily to hand in a way we have come to expect these days, but back in the mid eighties such things were still a novelty. Finishing off the typical Kawasaki ergonomics is a handy charging system checker mounted within the rev counter activated by a knob just below the dial, simply press the button and the voltage level present in the loom is shown.

So the old girl still stands the test of advancing time well, with so many modern day features and a great ability to corner, a well sorted GPZ still makes a good alternative to a modern bike. Cheap to run and very easy to maintain, with a good supply of after market and genuine parts, the GPZ is a viable run about for day-to-day use. The GPZ600 Ninja lived on until 1990 though by this time it was woefully outdated, as well as overshadowed by its sibling, the GPX introduced in 1988. Both the GPX models were not as sure footed as the earlier GPZ model, their shorter wheelbase, and steeper head angle, gave a skittish feel particularly under power.

Kawasaki saw fit to reintroduce the GPX in 1993 such was the interest in the older style machines. It was considerably lighter than the GPZ with an all up weight some 15kgs less than the 195kgs the Ninja hit the scales with, featuring thicker forks and  new brake callipers that gave a larger pad area. Quite surprisingly it was also 2kgs lighter than the benchmark CBR of the time while the two shared the exact same power output of 84bhp.

Kawasaki GPz600R Specification

  • Engine; liquid cooled 4-cylinder, 4-stroke, DOHC, 16-valve
  • Capacity; 592cc
  • Bore & Stroke; 60 x 52.4mm
  • Power; 73bhp @ 11000rpm
  • Torque; 42ft-lb @ 11000rpm
  • Transmission; six speed wet clutch chain final drive
  • Carburetion; 4 x 32mm Keihin CVK
  • Chassis; Steel box section
  • Suspension; 37mm telescopic forks, Uni Track” rocker arm linkage
  • Brakes; 270mm with single piston floating calipers  single 270mm, disc, single piston floating calipers
  • Wheels; 100/90 x 16  130/90 x 16
  • Wheelbase; 1430mm
  • Fuel capacity; 18 itres
  • Weight; 195kg
  • Top Speed; 135mph

Kawasaki GPz600R Gallery

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