In 1978, the world of motorcycles was turned upside down with the release of the Honda CBX1000. It was big, it was bold, and it was beautiful. Above all, it had six cylinders. The CBX was the first of the new era. For ten years, the big inline fours dominated motorcycling after the release of the Honda CB750. Before the CB750, twin-cylinder engines set the standard for high-performance bikes. Naturally, if four cylinders were great, six would be even better.
The CBX1000 was not an instant success. A year later, competitor Kawasaki released its own six-cylinder. The Kawasaki Z1300 was huge in a world where 1000 cc bikes were big. Not only did it have a transverse six-cylinder engine, but it was also liquid-cooled. And it had a shaft drive.
The big six-cylinder engine was the shape of the future superbike. And yet, by 1982, the Honda CBX had disappeared. The Z-1300 lasted a little longer, but in 1979 it also became history.
But the story of the six-cylinder bike is a bit more complicated than that brief appearance. And the six-cylinder bike is not dead. It still exists.
Imagine a 125cc five-cylinder inline four-stroke engine with twenty valves that can reach over 20,000 rpm. Honda made that a reality. A two-stroke engine produces more power than a four-stroke engine because it fires twice as often as a four-stroke engine.
Honda was committed to four-stroke engines, but in the early 1960s, two-stroke Suzukis and Yamahas were beating Honda in the 50cc, 125cc, and 250cc racing classes. The only way to win again was to increase power by increasing revs. And that could only be done by increasing the number of cylinders, making the moving parts lighter, and reducing the stroke.
In 1964, Honda launched the 250cc RC165 with six cylinders. It had a power output of about 65 hp at 17,000 rpm. The over-square pistons and connecting rods were made of specialized aviation alloy to withstand the stress, while two oil-cooled radiators were incorporated into the fairing to eliminate intense heat. This small 250 could reach speeds of over 241 km/h. Although they were great for winning races, these radical 125 and 250 bikes were extremely expensive and difficult to work with.
But the stage was set, and the improvement of technology and engineering led to the user-friendly four-cylinder CB750 in 1969. It easily surpassed the best parallel and V-twin engines of the time, and its design dominated motorcycling for the following ten years.
When Honda launched the CBX1000, motorcycle experts declared it the fastest production bike. The 1047cc DOHC, inline-six, 24-valve engine produced 106 hp. It could reach speeds of 218.8 km/h. These were astonishing numbers for that era.
But it wasn’t just the performance that impressed. The CBX also had a fantastic appearance. Although it had the same conventional layout as other large bikes of the time, Honda made the large engine a standout feature.
It was a glorious chrome block with six exhaust pipes that extended down and back. The whole bike had a generous size, even huge by today’s standards. The handlebars were wide and comfortable, and the spacious and comfortable seat perfectly complemented the large fuel tank. Later, it was revealed that Honda had visually adjusted the accessories to make the bike appear less bulky, with the gauges, headlight, and mirrors proportionally larger than those of similar four-cylinder bikes.
The CBX was a fantastic motorcycle, but also a bit strange. If we went from a 750 to the CBX, it was like trading a Ferrari for a Bentley. It was big. The wide seat was comfortable. The sound was a refined hum instead of a roar. Although the performance numbers speak for themselves, riding the CBX was like riding in slow motion. It didn’t scream in the corners; it leaned in a refined way. The acceleration and braking were equal. The CBX was expensive to buy and maintain. The CB900F, launched shortly after the CBX, sold much better. In 1981, the CBX was transformed into a sport touring bike, and its production ended in 1982.
The Kawasaki Z1300 was launched as a high-performance naked bike in 1979. The bike seemed to confirm the arrival of high-performance six-cylinders. The Z1300 made more noise because of its displacement than its number of cylinders. It was also water-cooled and had a driveshaft. It was a robust bike, larger and heavier than the CBX. To make the huge engine as narrow as possible, Kawasaki made the pistons noticeably undersquare. This reduced the width of the bike but limited the revs.
The Z1300 had decent performance, but when it was launched, the Suzuki GS1000 and Yamaha 1100 surpassed it in every aspect. The Z had a lower top speed and inferior acceleration to its Honda rival. However, it was a very comfortable bike and quickly transformed into various touring models. The Z certainly outperformed the CBX in several years, but it was the last of the strange and limited experience with six-cylinder motorcycles.
When Honda launched the CBX1000 in 1978, it was because the wonderful dominant inline-four series was coming to an end. Although the CB750 set the standard and the superbike as we know it, all the other Japanese manufacturers were making this bike format at this time. Honda’s star was fading, and although it was on the brink of a new series of high-performance bikes, it needed to be renewed.
The CBX was new, but it echoed Honda’s glorious racing heritage in the mid-sixties. It was new, fast, and beautiful, and certainly redefined the Honda brand in the short term, but it didn’t sell. Even at launch, the CBX was at risk of losing to the other big four-cylinders.
Benelli created the Sei 750 six-cylinder in 1972, followed by a redesigned 900cc a few years later. The Benelli 750 was a four-cylinder Honda 500cc with two additional cylinders. Despite being well received by the media, the Benelli Sei was a luxury motorcycle, an expensive and extravagant bike that attracted attention. But neither of the models sold very well.
More importantly, Honda’s six-cylinder Goldwing. Already an established touring motorcycle, in 1987 Honda introduced the 1500 flat-six. Later, this bike grew to over 1800cc and remains the top touring motorcycle.
BMW manufactures a range of 1600 six-cylinder touring motorcycles, which are very successful in this somewhat limited and expensive class of bikes. However, neither the Goldwing nor the BMW really fit within the scope of this story, so that can be left for a more comprehensive article on another day.
