Dimensions

Engine

ZX900

ZX900

2000 ZX-7R

We have attached a dimension comparison to a Y2K sport bike. Now this should turns out quite surprising. The 15 year old Ninja is still does not differ from a modern sport bike by more than 3 inches. In some dimensions it is even better. It has a lower seat height by almost 4 inches, yet the ground clearance is a inch and a half greater. Now that will have less stuff dragging in the twisties. Also it keeps the center of gravity of the rider lower. It has a wheelbase that is only 2.4 inches longer. Now this can easily be adjusted by shortening the swing arm but in all but the most flickable turns this difference is negligible. Weight is a big gap, but it is not difficult to pare 50 to 60 lbs off of a stock 900 Ninja. These are the main reasons we decided to resurrect a 1985 ZX900-R as our first project bike. We have no illusions that today's sportbike is on a plane than this vintage sportbike but we are curious as to how close we can come without spending the price of a 2K bike. Now be forewarned much of what we do to the bike is not found at the parts counter. Also trick parts we fabricate are one off items. But we will try to keep it to a level that a enthusiast with a good degree of mechanical aptitude can reproduce.
To the left the project bike. We already pulled it apart, but the condition is still clearly visible. The tank is dented one side cover is cracked. The upper fairing is salvageable but the center is pretty bad. The fender is cracked. We are debating about refurbishing the plastics on hand or trying to track down used pieces in good enough condition for paint. The frame and associated metal hardware is in good shape.
The cylinder head was not a pretty sight. We couldn't figure out how the water got in there. Fortunately the water did not get down into the cylinders or the bottom end. We were in luck though an had another head with only a pair of bent valves. So we stole a couple out of this head, cleaned them up and save our selves a ton of money. Hopefully your project bike does not have such damage. When it rains in Florida it does pour. Some how 15 years of summer storms caused this.
While our fix was cheap it was labor intensive. The bent valves were replaced and then the head was cc 'd and leak tested. Then all irregularities and casting flaws were ground out. Finally all of the combustion chambers were highly polished. CC-ing a head involves taking a graduated syringe and measuring how much fluid it takes to fill each combustion chamber. Then you remove material from each head until they all match the one with the greatest volume. Leak checking is done by filling each combustion chamber with light oil and seeing if any leaks away over a period of 24 hours. This head is ready to go back on the motor. Polishing the combustion chambers helps reflect heat. You also polish the piston domes. Reflected heat helps ignite the fresh fuel and aids in a more even burn. Also the polished surfaces shed deposits easier and less combustion heat is picked up by the metal of the engine, thus resulting in a cooler running motor. The exhaust gasses will be hotter though so those of you with chrome pipes will have a greater incidence of chrome discoloration..

The 900 Ninja's claim to fame is highlighted in the photo above. In 1984 it was a radical departure from the traditional motorcycle look and boasted the latest technological gadgets. It wore a 16 inch wheel out front with adjustable air or nitrogen preload forks adjustable damping and hydraulic anti-dive. The rear has a cam design chain tensioner, monoshock air/nitrogen dampening adjustable suspension. The swingarm was box tubular aluminum and a 18 inch rear wheel.

The engine was also brand new. Water cooled and the size and weight of a 750 motor. Kawasaki moved the cam chain from the middle of the crank to the left end and moved the alternator to above the cases and behind the cylinders. On top dual overhead cams actuated easy to adjust rocker arms that helped keep the height of the engine low. A plain bearing single piece crank rounded out the motors features. Carburetion was supplied by four 34 mm flat slide Keihin CV carbs. The Chassis was a over the engine triangulated steel frame utilizing the engine as a stressed frame member. The motorcycle had a detachable rear subframe. Wow now doesn't all that sound very familiar. It should it is the basis around which almost all modern sportbikes are built.

The final result was a bike that was a full bore 900 but the size and weight of most 750's of the time. So the next time you admire all of the modern technology on your new sport scoot. Take time an remember that in 1984 most of that first saw the street on this motorcycle. Next up the bikes vital statistics. Even by toady's standards this motor is no slouch. In the hands of a expert rider it could embarrass a less adept rider on much more modern machinery.