The Roots Of The CBX
Date: Thursday, February 19 @ 12:28:54 CST
Commonly, the origin of the CBX is being traced back to the sensational RC164 six-cylinder racer of 1966. And as the brain behind the racer was the same brilliant engineer, Soichiro Irimajiri, who created the CBX, the “blood-line” is quite obvious
Too many similarities between the two engines make it impossible to argue with this: DOHC, 4-valves per cylinder, six carbs, a jackshaft, driving accessories and even the “open bottom” tubular frame are elements found in both bikes. Many times, the few other examples of six cylinder bikes have been mentioned as a possible inspiration for the CBX. Kawasaki’s 1300, however, does not qualify for obvious reasons. The concept is completely different. The only interesting question is, how and why did both Honda and Kawasaki conceive a six-cylinder motorcycle and bring it to market almost exactly at the same time. Especially considering Honda’s story about the development of the big bike and how close they were to making it a Four. One can not free himself of the thought that “industrial espionage” may have been in play. A closer candidate for a legitimate “forefather” of the CBX, would be Benelli’s 750 Sei.
But a closer look unveils that this engine was actually inspired by Honda’s four cylinders, especially the 500 Four and as such somewhat of a copy itself. And although it was on the market earlier than the CBX, it came well after Honda’s RC and could not have been a model for Honda’s CBX engineers.
So, was there anything at all before 1966 that could have possibly been an inspiration for Soichiro Irimajiri to look at the inline-six concept and create a bike – a racebike, with an engine of half a dozen cylinders.
And if one digs deep into the vast archives of Grand Prix racing, surprisingly one indeed finds proof that Honda was not the first to have a six-cylinder race bike.
The mid 1950s saw an intense rivalry betweenthe major Italian Grand Prix contenders. In the 500cc class, Gilera dominated the circuit with its four-cylinder air-cooled DOHC 4-strokes. Between 1950 and 1957, Gilera won 31 Grand Prix races and six championship titles. MV Agusta was able to challenge Gilera in 1956 and won the title in that year. Both companies faced a thread by another manufacturer who had been competing in the smaller displacement classes but entered the 500cc class in 1955 with a sensational V-8: Moto Guzzi. In 1957, MV Agusta responded with an evolution of its 500 four in form of an in-line six , air cooled DOHC.
The engine was a 499cc, two-valve four stroke, six 26mm Dell’Orto carburetors fed the slightly “over-square” 48x46 mm bore and stroke dimension cylinders. The engine put out 75HP and was mated to a six-speed gearbox. It first appeared in MV’s line-up for the 1957 Italian GP but was only used for practice. After the 1957 season, Gilera, Mondial and Moto Guzzi stopped pouring money into GP racing and concentrated on commercial projects. Only BMW remained as a serious competitor to MV Agusta, who also made helicopters at that time, and MV shelved further development of the six. It did race once, however, in the 1958 Italian GP. The rider reported the bike to run at slightly higher rpm than MV’s 10,500rpm Four, but complained about the distinctively narrower power band . Factory records showed only a 5hp advantage over the 500cc Four.
Essentially the MV Agusta Six had the same fate as our Honda CBX. The lack of a significant performance gain over the same displacement 4-cylinder power plant, brought the concept to an end.
Comparing the rear views of the RC164 and MV Augusta Six shows a surprising resemblance. Although twice the size and 8 years earlier, the MV might very well have been the inspiration for Soichiro Ijimari.