I hope I have discovered a way to write fairly and accurately about the Honda CBX, a motorcycle that has been taken to heart as a super classic by some of us. CBX was designed as the logical ultimate in the developmental line beginning with CB750, passing through Kawasaki Z1 and the Suzuki GS liter bikes. The essence of this development was to put ever-larger, more powerful and heavier air-cooled four-stroke engines into chassis of a 1960s technical level.
The immediate motivation was to put upstart Yamaha back in its place. Yamaha, seeing Honda satisfied through the 1970s with cranking out pretty unexciting machines in every displacement, decided that Honda had abandoned motorcycles to concentrate on their fast-expanding auto business. CBX was the sharp point of Honda’s reply.
Shoichiro Irimajiri himself, designer of CBX and the GP racing sixes RC-165-6, admits that when, during CBX development, a four-cylinder 1000 was evolved from the company’s DOHC endurance racer, “It was extremely light and actually much faster than the CBX.
“Nevertheless, we felt there was something exhilarating and exciting about the 6-cylinder CBX that was lacking in the 4-cylinder CB1000F... something in the CBX that could not be measured in numbers like speed and weight, (something that) made it a very sexy machine.”
CBX arrived (1979) just as the AMA was pondering whether 1000-cc Superbikes were too much for existing tracks – the formula would drop to 750-cc for the 1983 season. In 1977 at Riverside I had seen every Superbike displaying the 2-3 cycle high-speed instability known as weave. A suspension and chassis revolution was coming, but the first bike to embody it – Honda’s 1983 Interceptor Superbike – lay in the future.
For that reason, CBX was given 250-sized 35-mm fork tubes and a chassis and swingarm of bicycle-sized tubing from which the engine hung in 1965 Superhawk fashion (no structure passed under the engine.
The engine embodied the best of the classic past - all that enthusiasts of the time could have hoped – six 64.5 X 53.4-mm cylinders totaling 1047-cc, with gloriously obvious double overhead camshafts (each with eight bearings!)and four valves per cylinder, set at the progressive (in 1967, at least) included angle of 62.6-degrees. Irimajiri would at one point say that the generous valve included angles of the era were necessary to provide room for cooling fins between the cam boxes. Tappets were the inverted buckets that had been through the GP wars of 1959-67 – in the race engines, tappets sat above the springs, carried in bolted-down bronze carriers, but in CBX they fitted down over the springs and worked directly in the head. There were six inward-angled 28-mm carbs to remind us all of the organ-pipe intake array of the great 250 and 297 sixes on which Mike Hailwood won four world titles.
There was consternation when it appeared for a time that Honda might apply pressure to homologate this “slant six” for AMA Superbike racing. However the detailed arm-wrestling played out, the CBX did not join this “vintage weave derby”, and for the last two years of production (1981 & ’82) a somewhat more modern fork tube size of 39-mm was substituted.
All the numbers added up to 105-hp at a fairly calm 9000-rpm (bikes with strokes longer than this now redline 50% higher). Dry/wet weights were substantial at 544/600-lb. The lightweight revolution of Suzuki’s GSX-Rs lay eight years ahead.
To allow a useful angle of lean, CBX crankshaft length was limited by not placing primary drive and alternator on its ends. In traditional Irimajiri/Mercedes-Benz fashion, power was tapped from the center of the long crankshaft (modern for the time in being a one-piece steel forging with all plain bearings and split-and-bolted con-rods) to pass by silent chain to a high jackshaft that in turn drove clutch and 5-speed gearbox. The two cams (each in two sections) were driven in classic Honda GP racer fashion from the center as well (by affordable chain rather than by noisy spur gears as in the RCs). Accessories were placed atop the gearbox.
Irimajiri notes somewhere that he ‘had previous experience’ with the torsional vibration problems of a six. It was Mercedes in its M196 straight-eight GP car engine of 1954-5 who cut the vibrating length of a very long crank in half by taking power from its center. Rolls-Royce in their great ‘Merlin’ V-12 aero engine had done the same by setting the ends of its 6-crankpin shaft “free” by placing spring drives between them and the loads they drove (propeller at the front, geared-up supercharger at the rear). And in Irimajiri’s 1960s six-cylinder GP cranks, built-up by multiple press-fits of limited strength to allow use of the needle bearings then believed essential, crankpins had been made in three sizes – biggest for #s 3 and 4, smallest for #s 1 & 6. The 250 and 297 cranks were made as light as possible, for the more mass present, the greater the problems with torsional vibration. Result; the six’s instant throttle response and its instant stopping once the throttle was dropped. There is a lot of unseen engineering here.
Just as the 1969 CB750-four resonated with public respect for all the races won by Honda fours, so the six ignited a helpless attraction to CBX because it had six cylinders like Hailwood’s winning bikes. It was unique. That attraction, for some of us, persists undiminished to this day in the form of cherished hulks (“I’ll never sell that thing…”), restorations, and extremely various customs. This is not to say CBX was for everyone – sales of so extreme a motorcycle were moderate, such that the company gave away some late models to tech schools.
Because I was immersed in AMA F750 racing with the Yamaha TZ750 at this time, CBX seemed to me irrelevant - a calculated too-muchness on its slow-steering American-LaFrance 58.9-inch wheelbase. But I didn’t reckon with the fires of enthusiasm that this six would set aglow for years to come. Just Google “CBX chassis” and see the many ambitious project bikes the six has inspired, to say nothing of the “paint-drip restorers” who vie with one another to create the most accurately perfect ‘original’ bikes (“if I can just get this thing exactly right, then it will be 1979 again.”)
CBX celebrated so many things, and continues to do so.