MT The Mighty Kawasaki Zed

These set performance standards for their time, but provided limited comfort, were excessively thirsty, and outside the mainstream of motorcycle design. Kawasaki then decided to follow another path, that of the four-stroke four-cylinder. With its 903cc Z1, Kawasaki managed to eclipse the performance of the H1 and H2, and create a user-friendly superbike. Considering motorcycle production for Kawasaki only began in 1963, the Z1 was a stunning achievement, and the recipe for instant success.

The heart of the Z1 was undoubtedly the engine. This intentionally differed to the Honda CB750 in many details, offering several features previously the reserve of exotic cars or racing motorcycles. The transverse four-cylinder four-stroke engine had square dimensions (66x66 mm bore and stroke) and displaced 903cc. Though the engine tune was very mild with an 8.5:1 compression ratio, 36 and 30mm valves, and four Mikuni VM28 mm carburettors, features such as double overhead camshafts and a nine-piece, pressed together, roller bearing crankshaft set the Z1 apart from the competition. The crankshaft was supported by six main bearings, with one-piece conrods. The primary drive was by straight-cut gears, the drive being cut directly into the flange of the number four crank counterweight. This resulted in a compact and direct primary drive system that minimised drive train snatch. Though the pressed-up crankshaft was an expensive solution, it was incredibly strong, and when welded together could handle enormous power outputs. Anticipating future environmental controls, sintered alloy exhaust valve seats allowed the use of lead-free fuel, and there was a positive crankcase ventilation system with an air/oil separator on top of the crankcase above the gearbox. With a environmentally quiet (84 decibel) four muffler exhaust system, the power was 82bhp at 8500rpm, making the Z1 the most powerful machine available in 1972.

While the engine set new standards for production motorcycles, the chassis was more conventional. The double cradle frame was constructed of mild steel frame, and there was a Kayaba front fork and poor quality Kayaba twin shock absorbers. The braking was marginal considering the power, but the single front disc was state of the art for 1972. With Dunlop K103 and K87 Mk II tyres, specifically designed for the Z1, handling was acceptable for the day but not outstanding. The dry weight was a considerable 230kg, but nothing else at the time could match its engine performance.

The Z1 became the similar Z1A in 1974, changes largely being limited to colours (the engine no longer having black-painted finning). With production numbering more than 80,000 units during 1973 and 1974 the Z1 was already on its way to being Kawasaki's most successful model. The Z1B of 1975 (featured here) lost the automatic chain oiler, the front forks received revised dampers and softer springs, and to improve low speed running there was a new automatic ignition advance. The Z1 may not be rare, but it is one of the most significant motorcycles ever, and an all-time classic.

(Ian Falloon is a Melbourne-based author who has written a number of books on marque histories.)