Four was sold from 1969 to 1970 and was available in
one of three colors: Candy Blue Green, Candy Gold, or Candy Ruby Red. The tank,
side covers, and upper forks were of the basic color (green, gold, or red). The
headlight shell was also the basic color. The bike had a 4-into-4 throttle cable
system. The exhaust system was a 4-into-4. The engine was a 736cc SOHC 2-valve
dry sump inline 4 cylinder linked to a 5-speed transmission and chain drive. The
serial number began CB750-1000001.
Honda's 750-four was the original superbike; the
machine that redefined the limits of motorcycle performance almost
overnight. Actually born in the Sixties it was unveiled at the Tokyo
Show in October 1968, and released in limited numbers the following year -
the CB750 dominated the early Seventies and had a huge influence on the
machines that followed it. Until the arrival of the Honda, with its broad
bank of aircooled cylinders and four shining mufflers, mass-produced fours
simply did not exist.
The CB750 changed all that and went further,
combining its basic appeal with a competitive price that included
refinements such as a disc front brake and electric starter. It was
the Honda's engine that created all the impact. The angled-forward 736cc
unit's design used many lessons learnt during Honda's days of racing
multi-cylinder machines in the Sixties, although the roadster relied on a
single overhead camshaft and two valves per cylinder, in contrast to the
racers with their twin cams and four valves per pot.
The CB750's output of 67bhp was mighty
impressive at the time, though, as were the smoothness and reliability with
which it was delivered. The CB was designed as an all-rounder, with a view
to sales in the important American market, but was good for over 120mph
despite its high, wide handlebars. Handling, however, was only
adequate, with the flex-prone steel frame and harsh suspension later coming
in for criticism. But in the excitement of the CB's arrival few riders were
put off by that - especially after veteran Dick Mann had proved the four's
sporting potential by winning at Daytona in 1970.
Honda sat on their laurels a little, barely
updating the 750 even when Kawasaki launched the faster 900cc Z1 four years
later. In fact, the CB was detuned slightly over the years to reduce
emissions. When Honda finally revamped it in 1976 with the so-called Super
Sports CB750F - complete with flat handlebars, bright yellow paint and a
four-into-one exhaust — the new bike's top speed was only 115mph.
The single-cam CB750 soldiered on for a full
decade, finally being replaced by the 16-valve CB750K-a disastrous bike that
combined poor handling with a series of mechanical problems. Bui the memory
of that first great superbike remains with the faithful.
Source of review: Roland Brown
One of the most significant
machines in recent motorcycling history, the CB750 Four
featured a 4-cylinder engine reminiscent of the Honda RC
racers. The 750 Four had a terrific exhaust note resonating
from four exhausts and, in a first for a production
motorcycle, a top speed of over 200 km/h (~125mph). The
incredible 750cc 4-cylinder engine featured a wealth of
technology developed from sixties era GP racers.
Features included Honda's
first one-piece crankshaft, a dry sump design and a level of
reliability never before seen. Like the RC racers, the CB750
was a high-rpm, high-power machine kicking out an un-heard
of 67 HP at 8,000rpm. Harnessing this impressive power was
an RC-type double-cradle frame and, in another breakthrough,
a front disc brake.
Other components, like tires
and chains, were also of especially high quality. The CB750
brought a new level of performance and sophistication to the
world of motorcycles, making it an instant top seller.
Truly, this was a machine that changed the history of
It is so clear as to be beyond argument.
Some will say that it is too heavy, or the suspension is too
stiff, or it is too quiet, or that four cylinders is too many
for a motorcycle. But the total is greater than the sum of its
parts. If the Four didn't run faster than 120 mph, if it didn't
turn a 100-mph standing quarter-mile. Most people take it for
granted that you can't lean a 500-lb. behemoth around turns like
you can a good Single or Twin, Fact: it is nearly impossible to
ground the 750. which allows as much, or more, banking than the
Superhawk. Further, the weight seems to provide little handicap
to proper handling. The springing is stiff, so the chassis is
traveling in the same direction as ihc rolling gear most of the
time. Cornering at speeds from 60 to 100 mph, the Four shows
very little tendency to "pogo" or shake its head.
It's easy to fawn over as a modern-day marvel, but it would be
more appropriate to say that the motorcycle industry, in its
present stage of development, deserves nothing less. What is
surprising about the 750 is that development of the complete
motorcycle took less than a year. Honda had not even decided the
basic engine configuration by summer of 1968. The choice of the
four cylinder design and its basic features was based, not upon
pure drawing board theory, but upon Honda's experience with
other racing and production engines. Even Honda's Grand Prix
formula car plays a part in the heritage of the 750. That it
would be a Multi was obvious - for greater efficiency. That it
would be an inline Four was based on the firm's seven-year
experience with four-cylinder racing motorcycles, as well as
more recent experience with production car engines.
The 750 follows the classic four-in-line pattern, with the outer
crankpins opposed to the inner two by 180 degrees. There is a
spacer between the center cranks to allow room for twin
single-row chain drive sprockets as well as the drive sprocket
for the single overhead camshaft. The five-main-bearing crank is
forged in one piece, turned on a lathe, heat treated and then
finish ground. Firing order is 1-2-4-3 (cylinders numbered from
left to right). Power is taken by chain from the center of the
crankshaft to the clutch by way of the mainshaft. Center drive
allows the clutch to be positioned inboard, reducing engine
width. There is relatively little difference between crank speed
and clutch speed, so the clutch size may be reduced, as it does
not have to bear the brunt of a severe gear multiplication. This
does, however, cause engagement to be rather sudden in relation
to the amount of movement the rider makes with the clutch lever.
Practice will overcome this one idiosyncrasy of the 750, so that
smooth starts will be a matter of course.
Use of chain, rather than gears, for the primary drive has clear
advantages. It simplifies crankshaft construction, for one
thing. The chain transmits power more efficiently, and presents
yet another way to reduce engine weight. While power transfer by
chain offers the possibility of snatching. Honda seems to have
eliminated it with the use of a spring-loaded rubber tensioner
for the twin primary4 drive chains.
Unusual (or unexpected, we should say) is Honda's use of plain
bearings in all major engine bearing surfaces including
crankshaft mains, connecting rods and camshaft. The public has
always associated Honda motorcycles with constant high rpm
running, to which the use of rolling bearings is also
associated. However, there is much argument in favor of the
plain bearing, and Honda's departure from its "usual" practice
docs not seem so radical if it is viewed in the light of the
company's use of plain bearings in its production car
engines-and even in its latest 12-cylindcr air-cooled Formula
One car. Compared to a rolling bearing of equivalent load
capacity, a plain bearing is lighter in weight, costs less to
assemble, and is smaller in size-all important factors in a
multi-cylinder engine that must be crammed into a roadable bike
chassis. The plain bearing is also quieter. In a Mulli. where a
greater number of bearings are required, they contribute greatly
to Honda's desired goal of silent engine operation.
As for load capacity the arguments are also in favor of plain
bearings. The maximum load capacity of a rolling bearing is at
zero rpm. and decreases as rpm increases due to flexing of its
components and fatigue.
The rolling bearing is commonly thought to be a friction-free
bearing. This is a myth. Rolling bearing components roll, which
creates friction, and the balls or rollers also have a tendency
to throw oil from their path. When properly lubricated, a plain
bearing tends to retain its cushion of oil and the cushion
becomes more effective with engine speed, a factor which
produces less friction.
Naturally, lubrication must be optimal with plain bearings, so
oil in the new Four is pressure-fed at 60 psi (ii never drops
below 30 psi even at low engine speed). It is worth noting thai
Honda didn't "mix" rolling bearings in with plain bearings;
Honda engineers reason that, as long as a high pressure system
has been created to lubricate plain bearings somewhere in the
engine, it makes sense to unify the system as much as possible.
This explains the presence of plain bearings throughout
camshaft, connecting rods and crankshaft.
Yet another reason for a unified pressure system is the heat
factor. Oil carries away heal, and flow must be optimal in these
critical engine areas. For the converse reason, the
transmission, which shares engine oil. is on the scavenge side
of the system: heat is less critical there. Naturally, rolling
bearings arc used for the main transmission components, as they
work best under lower pressure conditions. Both the engine and
transmission are dry-sump, for minimal oil drag. For the first
time, Honda has employed a separate oil reservoir, the main
reason being to make the engine package tidier and slimmer.
Another departure for Honda is the CB7S0's "undersquare"
bore/stroke ratio (63 by 67 mm. to give a displacement of 736
cc). No other bike in the Honda line has a long-stroke
configuration, and. at first glance, there seems to be no
advantage to engine efficiency in going undcrsquare. But. the
CB750's 8500-rpm redlinc acid power peak isn't all that high
(compare this to the 10,500-rpm redline of the CB350). So,
evidently, Honda has eschewed being at the top of fashion in
favor of narrowing the bore, to ultimately reduce engine width.
At 8500 rpm in a production engine, the narrower bore nukes
little difference in efficiency or piston speed: in fact, the
engine seems capable of being turned at much higher speeds, with
appropriate valve irain modifications.
The 750 is in an extremely mild state of tune, with
intake/exhaust valve overlap being not much more than that of a
good touring car. One of the reasons for this mild tuning is to
achieve tractability. Honda was successful in this tack, as the
750 may be pottered around town between 2000 to 3000 rpm. The
other reason for mild overlap is to achieve good gasoline
mileage, which was one of the three most important criteria set
up for the 750 before the engineers went to their drawing
boards. In one of our testing sessions, we subjected the 750 to
a six-hour "70 percent run." which would correspond to a
combination of fast touring and frequent sporting bursts from 65
to 110 mph through the swervcry. We achieved a figure of 29.9
mpg. which was extremely impressive under such agitated throttle
conditions. In steady freeway touring, the CB750 rider could
expect 25 to 30 percent better mileage, which would net about
150 to 180 miles on a tank of gasoline.
There is nothing unusual about the CB750's valve gear layout,
The valves arc operated by rockers, and paired inner/outer valve
springs. The tappets are easily accessible for adjustment
through rocker box caps, although the fuel lank must be removed
to reach them. There is one innovation in that the intake and
exhaust valves are offset slightly to minimize the possibility
of collision. While it may seem curious that Honda didn't go
all-out with a double overhead cam layout, it must be remembered
that the benefit from the extra cam would be doubtful for a
large-bore touring engine. Honda considers the reduced head size
of an SOHC engine to be of greater advantage, as it may fit more
compactly into the frame. There is also the consideration of a
DOHC engine's greater weight; the CB750 head, being sohc. weighs
hardly more tlian the dohc head of the smaller CB450.
The cylinder block is, in effect, split into two halves-two
left-side cylinders and two right, with a gap in the middle for
the cam drive. The finning is generous and each cylinder is
separated from the others by large air passages for optimum
cooling. The great flexibility of shaping is made possible by
shell mold casting. Honda engineers found that air cooling the
Four presented no problems al all. In testing of early
production models in high speed runs on the open-limit Nevada
roadways, cylinder head temperature was (he same on the inside
cylinders as it was on the outside.
Of most interest in the effective, but
mostly conventional chassis/rolling gear assembly is the
hydraulically operated singlc-caliper disc front brake. One of
its most welcome features is that the disc is cast stainless
steel, which does not rust, as do the non-stainless discs on
other disc brakes preponderantly available. As the disc is
exposed to view, it is nice to know that it will look as nice
after a few years use as when it came off the showroom floor.
There is a chance of more brake noise due to the use of
stainless, which has mediocre sound dampening quality. To
counter this. Honda has made the puck, or brake pad. slightly
spherical over its gripping surface. The puck is self centering.
Unlike several other double and single disc brakes we have
sampled, the Honda unit is not at all touchy. It is reasonably
fade-free for a 120-plus-mph machine and possesses enough
stopping power to break the front wheel loose at any speed.
However, the lever action must be firm to do so and there is a
responsive, broad zone of gradation between full-off and full-on
a decisive safety factor. This excellent feel and broad
gradation may be a by-product of rounding the brake puck
friction surface. When the brake is applied mildly, only part of
the puck may come into full contact with the disc. Full contact
and full stopping force is achieved gradually because the puck
must be highly compressed before the entire surface of its face
comes into full-pressure contact with the disc.
The CB750 frame is hefty, consisting of a full double cradle and
main tube, bolstered by two smaller auxiliary top rails. These
rails, joined to the maintube by triangulating struts, extend
straight back from the front downtubes to function as the top
rails of the rear subframc assembly. The swinging arm assembly
is mounted inboard of the cradle. The swinging arms arc
two-piece welded stampings, rather than the usual tubing; due to
the wall thickness and overall size of the arms, they should do
the job properly. Hard power-on cornering gave no evidence of
As mentioned before, the suspension gives a comfortable, but
decidedly firm ride. Evidently the rear spring/damper units
(nitrogen-sealed non-serviceable De Carbon shock absorbers) are
at the peak of stiffness for a single rider weighing 160 lb.
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