The following article appeared in an excellent book published by Quintet (Apple
Press) called 'The World's fastest Motorycles'. Published in 1988.
ISBN 1 85076 067 5
Latest, maybe last, in a line of across-the-frame fours directly descended from
Honda's first superbike, the swift CBX exhibits steady progress. The power unit is more compact, more powerful,
and maybe more civilized, the bike handles much better, and goes 2Omph faster. Amazingly, 15 years have also made
the engine design seem relatively simple, compared with the later water-cooled machines.
The CBX750 could well be Honda's last offering in the classic, inline four cylinder
750 family. The factory are now firmly committed to V4 engines powering their large sports bike and the future
for any large, air-cooled, inline engine is uncertain. The release of the CBX marked the end of 15 years of uninterrupted
CB750/4 production, involving countless revisions, new engines and updates. Honda were the first to launch an inline
750/4 - the original superbike - back in 1969. It used a SOHC, eight valve engine and produced 67bhp. For comparison,
the CBX750 features a DOHC, 16 valve engine and produces 91bhp.
The CBX differs from its many predecessors in some significant ways. The top end
of the motor is remarkable for employing hydraulic tappets, hardly a new idea (Harley-Davidson have used them for
decades) but unique on a Japanese production motorcycle. The advantage to the owner in not having to set 16 valve
clearances is obvious. Honda have added thin stemmed lightweight valves making for less reciprocating weight.
Weight saving and compact design are in evidence everywhere on the engine. Its
width was reduced by placing the big 32OW alternator behind the cylinders instead of spinning on the crank end.
Height was reduced by making the sump shallower and redeploying the front frame tubes as oil carriers, a novel
redistribution that actually increases the total oil capacity. Finally, Honda pruned the engine length by dispensing
with the jackshaft between crank and clutch. Primary drive is by direct gear from the crank; one of the crank webs
has been turned into a gear pinion.
Engine performance is marked by smoothness and excellent tractability. The CBX
makes good low-down power aided by some low gearing. The mid-range is a bit flat and lacks snap but acceleration
is very healthy at the top end, above 8,00Orpm. The bike is so smooth and uncannily quiet at speed that Honda deemed
it necessary to fit a rev limiter that cuts in at 10,80Orpm.
The engine's compactness means that it can be mounted lower in the frame, partially
compensating for its inherent top heaviness. The steering is very quick, and handling and roadholding are exceptionally
good for a bike of this size and weight.
The CBX is genuinely flickable, largely because of its low frontal area and careful
weight distribution (48.6/ 51.4 front and rear). It is stable up to top speed though the smart and sleek half-fairing
is more of a sports cockpit than a touring windcheater. The dual headlights are a bonus for any road user, 12OW
of sharp illumination on dip or main beams.
Although the release of the CBX750 marks the end of Honda's development of inline
engines, the bike is a shade quicker and more powerful than the V4 VF750 which was also released early in 1984.
The second generation V4 750, the VFR750F, is based on Honda's successful endurance race bike. It has gear driven
cams and makes 105bhp at 1 1,00Orpm. Development and progress go on as ever, but will they still be making V4 750s
in 15 years time?