Kawasaki and high performance motorcycles are synonymous, and the machine that created this legend was the incredible two-stroke three-cylinder H1 Mach III.
Introduced in September 1968, the H1 was raw, and untamed, with an unmatched power-to-weight ratio. While the Honda four offered sanitary performance, the H1 was the motorcycle every adolescent dreamed about. The H1 may have been flawed, with a reputation for twitchy handling, but no other production machine, regardless of displacement, could match the 500cc H1’s scintillating performance in 1969.
Development of the H1 began in early 1967, and it was a new design, sharing little with existing Kawasaki rotary valve two-strokes. Epitomising the era when engines overwhelmed the chassis, the H1 was dominated by the air-cooled three-cylinder two-stroke engine. The cylinders were inclined 15 degrees, and the 499cc in-line three-cylinder piston-port engine had dimensions of 60×58.5mm.
During development much attention was paid to cooling the central cylinder, and the outer cylinders’ fins cropped on the inboard side to provide extra central finning. To produce high horsepower required a large port area, and this resulted in a relatively long crankshaft, exacerbated by the ignition distributor on the right and alternator on the left.
The ignition was innovative, and the H1 was the first production street motorcycle to feature a pointless electronic ignition, with surface gap spark plugs specifically designed to prevent overheating and oiling. Carburetion was by three Mikuni VM 28 SC carburettors, and with individual expansion chamber exhausts, the engine produced 60 horsepower at 8,000 rpm. For 1968 this was an astounding figure, and provided the 180kg H1 an unparalleled power-to-weight ratio.
While the three-cylinder engine was an undoubted tour-de force, when it came to the chassis and running gear the H1 needed more development. The double cradle frame, while loosely copied from the featherbed Manx Norton, wasn’t really up to handling the power. Neither were the slender forks, justified on the grounds that thicker fork tubes led to overheating of the central cylinder.
As the wide engine needed to be mounted high in the chassis for acceptable cornering clearance the centre of gravity was high, and while the wheelbase was a short 1,400mm, with 57 percent of the weight on the rear wheel the H1 wasn’t renowned for high-speed stability.
Another weakness was the braking system, the 206x35mm twin-leading shoe on the front and 180x35mm single leading shoe on the rear, prone to fading after repeated use. But the H1 was intended to go, not stop, and this it did like no other motorcycle of its day. Capable of a standing 400 metres in around 12.8 seconds, and a top speed of 200 km/h, all the rider had to do was stop regularly to quench its voracious appetite for fuel. Over the next few years the H1 was gradually softened.
The weight went up and the power down, the front end gained a disc brake, the wheelbase increased and eventually the motor was rubber mounted. By 1976 the wicked 500cc triple of 1969 was a distant memory, replaced by the slower, sanitary KH500. Overshadowed by a new era of Superbikes the Kawasaki triples were considered thirsty dinosaurs, without a raison d’être. But that has changed. Today the air-cooled triples are appreciated for epitomizing the era when Kawasaki dared to be innovative and different, and created unique and charismatic motorcycles.
Australia’s go-to-guy for classic motorcycle wisdom. Ian has written nearly 45 books on motorcycles that each offer unparalleled insight on the historical and technical development of particular makes and models.