Honda CBX - Original Cycle Magazine Article from December 1978
Two years ago, in a Los Angeles airport motel room hidden among other motel rooms and accessible only through a warren-like maze of passages, a late afternoon meeting was taking place. The meeting had been arranged at the request of Mr. Tadashi Kume, the Director of Honda Research and Development, and included other Honda R&D personnel from Japan and the United States, representatives of American Honda, and a small selection of motorcycle journalists. Mr. Kume came quickly to the point. "What do you think of Honda motorcycles?" he asked. Sensing that Mr. Kume hadn't come thousands of miles to exchange pleasantries, the American journalists were direct.
"Hondas embody the soundest engineering in all of motorcycling. They have proven to be reliable. They're beautifully finished, and they all perform well. "But it seems to us that Honda's current street offerings are not really new. The 750 has been with us since 1969. The 550-Four is essentially the same bike it was in 1971, and we haven't seen much significant progress on the 450 twin either. The 360 twin is adequate but not much more.
"We suspect that something has changed at Honda since the late Sixties. Back then, your bikes were replaced frequently with ones which were genuinely better. But during the past several years the company seems to have grown static, conservative. It no longer moves as fast or reacts as quickly as it once did. Everyone looks to Honda for new expressions, new ideas, new solutions; but recently, Honda has been plodding along. Certainly progress has been made. But progress is not the same thing as excitement. Hondas are no longer exciting." The journalists suspected Mr. Kume was not hearing anything he didn't already know. The time had come, Mr. Kume concluded, for Honda to produce a cosmic haymaker of a motorcycle that would catch the state of the art right in the ten-ring and put all the pretenders back where they belong. Honda, after all, had lost a good deal of its performance image. There were no Hondas racing on American pavement. There were no Hondas winning performance comparison tests, and no Hondas causing crowds to form and jaws to drop. Not so long ago the brightest of motorcycling's bright stars, Honda had turned into a background shade of dowager-gray. In the mind of Mr. Kume, the time had come for that to end.
Monday, October 24, 6:45 a.m. We are at Willow Springs Raceway this dark, sharp morning to see, to feel, to ride a motorcycle about which much is rumored but nothing is known. We hear it before we see it: a whistling Porsche-like snarl cuts through the coldness as the big Honda is warmed by one of its four attending mechanics. Just as the sun comes up we draw close enough to make it out. It is difficult for us to retain the calm all journalists aspire to.
Four days later-two at Willow Springs, one at the Webco dynamometer, and one split between Orange County International Raceway and Honda's R&D facility in Torrance - we came to believe that in the 1047cc, 24-valve, four-overhead-camshaft CBX-Six, Honda had the haymaker it wanted. There are flaws here and there, signs of haste and certain ambiguities. But the objective - to build the fastest production motorcycle available for sale anywhere in the world - has been met. The bike is more than fast; it is magic. The exploding glitter of its technical credentials lights up the sky. To know the motorcycle is to know the only rules Honda follows are Honda's own.
The CBX comes from many places. Its project leader, 37-year-old Shoichiro Irimajiri, was in his mid-twenties when he designed both the 250cc and 297cc six-cylinder GP race engines, the 23,000 rpm, two-cylinder 50, and the 125cc five.
"When we were racing," Irimajiri explained, "we were up against the four cylinder two-strokes built by Yamaha and Suzuki. Cylinder multiplication was the only way we could be competitive. That's why we built the Five, and the two Sixes. The CBX-Six is a direct descendent of those race engines. That's one reason it only took a year and a half-we had the engine technology from our GP racing experience."
If the CBX has its mechanical roots buried in the glory years of the Sixties, the reason for building it - or more precisely, not building it sooner - connects with Honda's growing interest in automobiles in the early 1970s. Until the end of 1974, Honda had but one research center, located in Wako. The good engineers - including Irimajiri - were at work on the CVCC engine and the Civic. Those projects completed, another research center - located in Asaka - was established. The automobile and power products crowd stayed in Wako; Irimajiri and the rest of the motorcycle people moved to Asaka. The first project out of the reorganized Wako facility was the Accord; the first bikes out of Asaka were the 400cc, three-valve Hawks.
At Honda rookie engineers work on racing projects while the experienced veterans design the motorcycles the company sells to the public. While Irimajiri and his friends were building GP racers in the mid-Sixties his superiors were designing 450 twins and CB750s. But as time went by the experienced veteran engineers grew older, and their places were taken by a new generation: Irimajiri and his go-go young friends, frolicking in the lap of mighty Honda and pushing back against the restraints of convention to make room for their own ideas.
When Mr. Kume returned to Japan after his meeting with the journalists, his desire to pole-axe motorcycling with something beyond the realm of the probable dovetailed smoothly with the situation at home: a new research facility and a fresh batch of gifted young engineers, designers and stylists all blazing with new ideas and all exceedingly hot to trot.
Initially Honda R&D went forward with not one engine concept but two: the Six and a 1000cc four-valve Four. For the first six months both engines moved ahead in parallel development, and then the decision was made to go with the Six, even though the Four had been persuaded to produce only five fewer horsepower (98, as opposed to the Six's 103, measured at the crankshaft).
The Six was selected because it had more long-term potential based on Irimajiri's GP race engine experience, because the Four lacked the Six's smooth delivery of power, and because the Six had a feeling and a sound that only comes from Sixes. From the beginning the CBX was a four-valve engine, for obvious reasons: more engine speed equates with more engine power. Since in at least one regard engine speed is governed by the weight of the valve assembly, and since four small valves can be made to weigh less and are easier to control than two big ones, and since Honda probably knows more about four-valve engines than any other combustion engine manufacturer, and since a label on the fuel tank which reads "24 Valves" was thought to have special appeal, the choice was automatic, easy and quick.
Subsequent problems were more challenging; subsequent decisions were longer in coming. One of them had to do with the placement of that beast of an engine, and brought Irimajiri and his eight-man engine team into active contact with Norimoto Otsuka and his team of five designers. Otsuka, Honda's Chief Designer with direct responsibility for the styling of all Honda motorcycles sold in North America and Europe, saw the Six the same day the decision was made to select it instead of the Four. "The first time we laid eyes on it," Otsuka said, "we thought, 'great!' It was such a new bike, with so many new ideas and concepts. We knew it would be difficult. But we were all very excited about the possibilities, since it was such a big departure from anything we had done before, both in terms of its technical specifications and the kind of look and feel the bike had to have."
Immediately Otsuka realized that the bike needed more between-the-knees room for the rider. From that came two significant engineering decisions: to tilt the engine forward in the chassis 33 degrees, and to mount the carburetors on V-shaped manifolding so that all six of them angle in towards the centerline of the motorcycle.
Achieving a satisfactorily narrow knee-to-knee dimension was but a single subcategory of the major engineering and styling problem, "Engine Width." At the very heart of the solution is what Irimajiri identifies as his favorite component: the jackshaft. He likes it because it made the six-cylinder engine a feasibility; he likes it because it posed a very difficult design problem in that so many forces act on it; he likes it because it has to do so many things. The jackshaft is turned by a 34mm-wide Hy-Vo chain driven by a sprocket machined in the middle of the crank. One end of it drives the alternator. The other end times the ignition, accommodates the starter motor gear and carries power from the crankshaft to the clutch housing, which in turn spins the oil pump through sprockets and chain. Conventionally, both the alternator and the ignition system are driven directly off the end of the crankshaft; this is true of all modern multicylinder motorcycle engines. But because the CBX is a high-performance sporting bike in need of cornering clearance commensurate with its character, and because six cylinders all in a row occupy a large and irreducible amount of transverse territory, to hang the alternator and the ignition on the ends of an already broad crankcase assembly was unacceptable. From end to end, the CBX engine measures 23.4 inches - only two inches more than the CB750. The jackshaft makes this possible. That's why Irimajiri feels such a warm affection for it.
In nearly every case the race track is the enemy of the street bike. A race track is not a road. It has been designed for one purpose: to cause separations and create gaps between riders and between motorcycles, and thus to convert a random assortment of competitors on the start line into a carefully ordered procession of truth at the finish. The track provides an opportunity for the rider to spelunk on down to the dim-lit basement of his motorcycle, where its character is kept. Motorcycles built for racing-TZ750 Yamahas, RG500 Suzukis-maintain coherent dialogues with the track. Street motorcycles as a rule do not, the track asking many questions they have not been engineered to answer.
Still, the basement is the basement, Willow is Willow, and this is where the CBX has been brought. Two immediate realities present themselves: the CBX's speed is disguised by its smoothness and its buttery spread of engine torque; and while its high-speed handling is certainly acceptable considering what it is (a street bike) and where it is (a race track), it has been incompletely developed.
Climbing on the bike for the first time, the journalists were awed by the bulk below and in front of them. Its cistern of an engine in no way intrudes into the rider's space, but parts of it seem always to be in the line of sight. And any impression of the fuel tank as a tight-skinned sculpturing vanishes when the tank is viewed from the saddle. From there it takes on a rounded, flowing voluptuousness made necessary by the bridgework beneath it. The seat is comfortable, and close to the ground. The handlebars, a pair of black aluminum forgings clipped to the tops of the fork pipes and drilled for lightness, are exactly where they ought to be - and can be adjusted if they're not. The fuel tank filler apparatus reflects stylist Otsuka's quest for the appearance of function: it's large, finished in black, and is secured not only by its own threads but by a polished hasp which swings down across its top and locks in place. This mechanism is derivative of nothing, but evocative of performance and efficiency. Below the instruments, a voltmeter; below that, a pod where idiot lights are displayed; and below that, mounted on the top triple clamp, is a covered fuse box.
The bike's rear springs were immediately adjusted to maximum preload, the engine was brought to an acceptable temperature by the attending technicians, and the high-speed laps began.
Willow Springs is called a "rider's track" by practically everybody, especially those most familiar with it. It has a downhill front straight, Turn One is a nick-'er-back-to fourth banked lefthand sweeper, Turn Two climbs forever uphill to the right, and Turn Three is another left, this one going off-camber just when it shouldn't. The next one jogs right, tips off-camber and charges back down the hill into a lower-gear left, also off-camber. Turn Seven skids off-camber at the top of a rise, Turn Eight is a flat right that can be taken at the limits of bravery and stability in fifth gear, and it leads into Nine, a tightening lightly-cambered right that has put more riders into the desert than Barstow-to-Vegas.
Going faster and faster as familiarity grew, riding impressions began to coalesce. First: the engine is so smooth and so snappy that the tachometer must be observed at all times or else the white-tipped needle lives forever in - or beyond - the red zone. The engine makes a lot of power - no great surprise there - and gets down to serious work once 6500 to 7000 rpm is achieved (the power peak is at 9000 rpm, the red line at 9500). At high speeds the rider is hardly aware of the engine at all; beyond a rushing highpitched hoot there is no noise to hear or vibration to feel, and one is left with a curious sense of distance from it, despite its size. Both journalists had just finished testing the Yamaha XS Eleven; both knew enough not to draw premature conclusions, yet both felt the Eleven had more engine clout than the CBX. Both were wrong.
Handling: touchy. Here today and gone tomorrow in some corners, here today and here tomorrow in others. By and large the CBX countenanced Willow with grace. There are no impediments to banking angle on the bike's right side; the sidestand limits it on the left, but not in any way that could be described as dangerous. Through the first seven corners high-speed stability is excellent for a big bike, or even for a small one. There are no wobbles, no wallows through these seven, yet the CBX must be ridden with care. It does not suffer sloppiness gladly. Deceleration is a good example. The entrance to Turn Four is riddled with bumps, and two downshifts-to third, then to second-must be made as the bumps are traversed. If the rear brake is applied too hard, or if engine speed doesn't match ground speed after a downshift, the bike hops its rear wheel in a busy display of irritation, a condition that worsens as the rear shocks get hot.
Exiting Turn Four also gave some exciting moments. The exit, off-camber, finds the CBX in second gear with its revs up. Get boisterous with the throttle and the back tire spins, which if not instantly controlled will put you on your head. Turn Four does that to all motorcycles; it is especially hard on the CBX, because of the bike's stupendous power output. If caution must be taken with braking, so too must the rider be smooth when initiating a turn. The story on the CBX is this: plan ahead. The bike is not thrilled to death if it has to make a mid-turn correction, nor does it appreciate being flipped abruptly to its maximum banking angle. The rider never forgets that it's a heavy bike; it has a heavy engine with a high center of gravity, and quick flips overcompress its suspension and lead to the flounders. But if the rider is precise and thinks about what he's doing the CBX rates as high-average in the race track handling department.
Except in Turn Eight. When the CBX comes upon Willow's Turn Eight it is belly to the ground, indicating over 120 mph. Specialist bikes (either GP racers or AMA Superbikes) frequently can be stuffed into Turn Eight wide-open. Generally, the CBX cannot. As soon as the first part of the corner is negotiated the bike begins a long, slow, disquieting wallow that can be subdued only after the throffle has been rolled back.
This behavior was noted by both journalists and was repeated for most of the two days. But on the afternoon of the second day the technicians replaced the slightly worn rear tire with a new one, traded the rear shocks for a fresher pair with a higher spring rate, and installed a front fender that had a beefier between sliders mount. For the following five laps the CBX's handling approached excellence; the bike could be turned quicker, the Turn Eight queasiness disappeared, and the bike was overtaken with a sense of solidarity it had not displayed before. But on the sixth lap, and all subsequent ones, it returned to its old habits, leaving the journalists with the impression that the rear dampers have no business being where they are, which is attached to this motorcycle.
The swing arm is almost as suspicious as the shocks. It's slender, tapered, uses plastic swing arm bushings and pivots on a bolt that looks like it came from a moped. In this area, the motorcycle is incomplete and inconsistent.
In addition to the performance of its engine, the CBX is superior in two other areas: its drive line and its brakes. CV carbs and all (which will be discussed later), the CBX is the best of the big Japanese motorcycles in terms of driveline snatch: none was noted, period. Irimajiri explained that the fact that it is a Six has much to do with this. Snatch, he explained, depends to an extent upon how much torque is applied to the crankshaft during one revolution. The problem can be eliminated one of two ways: add a large amount of flywheel weight (BMW-style), or increase the number of cylinders and reduce the one-rev torque figure. The CBX's clutch is a model of light, progressive engagement, and its gearbox, while clunky in the lower gears at moderate engine speeds, provides precise engagement at full-hustle. In two days of whipping around the track, the journalists missed but a single shift between them, which caused the engine speed to soar past 11,000 rpm but did no damage.
The CBX's brakes-especially those on the front-perfectly exemplify Honda's belief that the CBX will be bought and ridden by expert-level motorcyclists. The lightweight, 5mm-thick front rotors are from the GLl000; the rear rotor is unique to the CBX and has been thoroughly trimmed for lightness. Front calipers are from the 750; the rear is the same as the GL's. What makes the CBX's front brake unique is its extraordinarily powerful, light action. The components may look familiar but the ratios have been changed; the brake lever travels farther and takes less pressure than any current big bike's, and the result is stopping power you wouldn't believe. The current trend on dual-front-disc bikes is just the opposite: less lever travel, more lever resistance on some, just more resistance on others. The trend is responsive to the amount of trouble the average rider can get himself into if he grabs a race-track handful of double disc brakes without knowing what he's doing. No part of the CBX was built for average riders - most especially the front brake system.
When the journalists returned to Los Angeles one of them called racing instructor Keith Code. Code has a rider improvement school based at Willow Springs, and a wealth of experience with big street bikes at that track. How fast, he was asked, could a pure-stock Superbike negotiate Willow? "Anything under 1:50 is awfully good," he said. "A 1:48 would be exceptional, and a 1:45 would be about as quick as any stocker has ever gone."
On Tuesday afternoon, piloted by a rider who would not only have to fall on his sword but do push-ups on it were he to make a mistake, the CBX turned in a 1:43.
We were not alone with the CBX and the Honda engineers and technicians at Willow Springs. The bike had been brought to this howling wilderness for two reasons: for us to test, and for Honda's agency to film. The Six represents many things for Honda: the depth of its engineering and styling talent, its reawakening interest in high performance, its willingness to rush in where angels fear to tread. The bike is in every way a brutish delicacy, and will be greeted with loud hurrahs when the dealers see it for the first time. To that end Honda had organized dealer meetings in Hawaii and in Japan, at which the CBX would make its celestial entrance.
The problem at Willow Springs was this: the dealer meetings were still a month away, and if information or photographs leaked out early Honda's plans to surprise and delight its dealers would be ruined.
Not only that: the CBX found itself in the California desert under circumstances which could only be described as precarious. Motorcycles are developed for Honda Motor Company by Honda Research and Development Company, which was given its freedom from the parent company in 1960 by Mr. Soichiro Honda himself. R&D's corporate independence is buttressed by its fiscal independence; it is funded by a fixed percentage of the parent company's gross turnover. Traditionally, R&D packs up its new models when the designs are complete and the prototypes are running, and embarks upon the Grand Promenade over to Honda Motor Co. to present the new bikes to the parent company executives.
The CBX-Six left Honda R&D, all right. But it was mysteriously intercepted by the highwaymen at American Honda Motor Co. When it should have been making its bows before the smiling Honda directors in Tokyo, it was instead humping around Willow Springs for us and for American Honda's film crew.
This combination of conditions had nerve endings lit up like tiny prairie fires. Security was drawn down tight; either the CBX was being filmed or ridden, or it was shrouded in covers and tarps, a diamond in a gunny sack. There were documents to sign which by their nature discouraged any loose conversation, and guards to keep out the riffraff. On Tuesday, October 25, the riffraff included Gene Hackman and Paul Newman, who had come to Willow for a spin in their race cars only to be deflected at the gate, and Paul Newman's airplane, which tried twice to land on Willow's straight and finally gave up.
Although from one end of the crankshaft to the other the engine's width is not unacceptably beyond the norm for current multis, the CBX's beaminess extends from its crank ends all the way up to the cam cover instead of pinching in at the cylinder base surface. Viewed from the front, KZ engines and GS engines and XS Eleven engines describe the shape of a thickly-drawn inverted T; the CBX engine is a rectangle.
Except for one area: directly below the crank end-covers. Since a six-cylinder engine is so inherently smooth, Irimajiri was able to scrimp on counterweighting. The crank's two end bobweights - to the left of rod # 1 and to the right of rod # 6 - are roughly half the thickness of the other ten, and their outer faces are cut back at the periphery. The space needed for them in the lower case half is thus reduced, making room for bevel-cuts which improve the CBX's banking angle-even though some of the cornering clearance provided by the bevels is stolen by a pair of case bolts on each side.
If in terms of smoothness and power output an in-line six-cylinder engine could be called a mixed blessing, so in terms of cornering clearance could it be called a mixed curse. A six poses many problems; by its nature it also provides many solutions to those problems. The crankshaft layout is an example; the exhaust system is another. While it would seem obvious that a 1000cc Six would need more total muffler volume than a 1000cc Four if the two engines were in comparable states of tune and if both were responsive to the same decibel laws, such is not the case. There are two reasons for this: first, the displacement of each of six cylinders is smaller, making for smaller bangs. Second, a four-cylinder with a two-into-one exhaust arrangement and the standard firing order subjects each muffler to irregular exhaust cycles. The spark plugs fire at 180-degree intervals, then that cylinder pair rests for 540 degrees. But the Six, with three cylinders exhaling into a common muffler, has its exhaust pulses spread more evenly. Therefore a Six with a three-into-one exhaust (or six-into-two, if you prefer) can get by with smaller, lighter mufflers than a comparable Four, and smaller mufflers have less of a chance to drag the ground than larger ones. To make sure that mufflers do not spark against the pavement, the CBX's angle up and in at the rear.
It all works. After two days of hot-lapping around Willow Springs there are no hero-scratches anywhere on the exhaust system, even though the sidestand foot and the curb-feeler nuts at the ends of the footpegs have been frequently scraped.
Honda has always used careful exhaust system design to extract horsepower. But when the young engineers sat down at the banquet that was to be the CBX they reached beyond conventional aspirations of exhaust performance and towards the outer limits of motorcycle fantasy.
The journalists are at dinner with Mr. Irimajiri, Chief Designer Otsuka, American R&D Research Administrator Ken Nakagawa, and Senior Research Engineer (and former racer) Minoru Sato.
"From the beginning," Irimajiri explained, "our Six produced a smooth jetlike exhaust sound. But with an ordinary exhaust arrangement, it wasn't that close to a jet. We thought if we worked on it we could come up with a motorcycle sound like no one has ever heard before.
"So we sent some engineers to the Hyakuri Japanese Air Force base in Chiba prefecture. For ten days they tape-recorded the sound of Phantom jet fighters, and then came back and designed an exhaust system for the CBX that could duplicate that sound. When I heard it for the first time I was amazed; they had captured the Phantom sound perfectly."
"I rode the bike at our Suzuka test circuit," Sato said. "We had the HERT endurance racers out at the same time. It was crazy. The Six, with its Phantom exhaust, made me feel like I was going 200 when I was only going 100. The bike's sound had a feel - a noise quality and texture - completely different from anything I have ever experienced. It sounded better than the HERT bikes."
"After that," Irimajiri went on, "we contacted Mr. Kume. We told him we had something we wanted him to hear. He came, he listened, and he said, 'You've gone too far. The feeling of that noise is just too much. We cannot build motorcycles that sound like jet fighters.' "
So, Irimajiri concluded, they had to scrap the Phantom exhaust and build something more sensible. Now the bike sounds like a Porsche. But somewhere, collecting what passes for dust in the hospital-clean Asaka research facility, in the company of other experimental components which like Hemingway's Old Man went out too far, rests a mystical arrangement of pipes, tubes, baffles and screens which if attached to a certain six-cylinder, 24-valve engine, gives off the transcendental whoop of a deadly weapon of war.
The bike, as a styling exercise, is lean and elemental. Otsuka is responsible for this, and admits that the bike was nettlesome. Not just because of the size of its engine, either. It is a high-performance bike, and to express high performance in styling is "most difficult." The motorcycle emphasizes its own performance function by being what it is; the styling has to evoke this, and must never lead the imagination down the garden path toward conclusions of any other kind. There were spatial and mechanical problems to solve at first, and these - like providing room for the rider's knees, and keeping the weight down-were beaten back as Otsuka and Irimajiri reached compromise after compromise. Otsuka then began to shadowbox against the flickers and ghosts which populate the stylist's world.
Styling can be many things. It can festoon the surface like decoration; it can burrow into the shapes of components and structures and tweak one's impression of their purpose; or it can-and this is the toughest of all-clear the space between the observer and the function of the object, so that nothing stands in the way of the capabilities of the device he is observing. This can be attempted by the stylist only if the superior function of a given device is its main message. Apply the philosophy to anything else - anything less - and the result is caricature at best and at worst, deceit.
In the CBX Otsuka knew he had the essence of function, and so his task became one of transmitting that message unhindered and without modification. The fuel tank shape responds only to the demand for capacity, the design of the chassis and the physique of the average rider. The side covers, truncated triangles finished in black, are essentially that: covers. Otsuka's only extravagance, if you accept that the tank striping controls that vessel's visual bulk, is the seat/tail section. An extraordinarily light (5 lbs.), fully-detachable component, the tailpiece has a little kicked-up spoiler. Otsuka admits it does nothing whatsoever except pantomime in miniature the rear deck wing of the modern Porsche which, he elaborates, does nothing on the Porsche either. Beyond this frippery the CBX does not appear to have been styled at all - which is far from the cruelest thing one could say about Otsuka or his understanding of what the bike is, and can do.
Early on, however, he ran into a problem with the instrument console. His department fashioned a contemporary arrangement that was handsome and informative. But the engineers turned it away, saying that it didn't look functional.
Back to the jets. Knowing that aircraft pilots have vast arrays of instruments to monitor and not much time to do it, and knowing that aircraft instrument designers have from the beginning recognized function as their only deity, Otsuka saw and assimilated cockpit after cockpit, altimeter after air speed gauge, intercom switch after exhaust gas analyzer. What he learned was studiously incorporated: glare-free glass, black backgrounds, bright, simple numbers and long thick needles with white tips. It looks easy. It was not.
We had not been in the company of Mr. Irimajiri for more than twenty minutes before he mentioned his two biggest problems with the CBX. Engine width of course was one; overall weight was the other, and while he subdued the first with some flashing strokes of engineering brilliance, the second became a long-term battle in the trenches. From front to back, from bottom to top, the CBX is a monument to his thoroughness in pursuit of the dreaded gram. This is what he did:
Aluminum triple clamps, top and bottom; sliders and fork pipes machined internally to reduce wall thicknesses where stresses were low; a plastic front fender; aluminum-spoke wheels (4.4 pounds lighter than steel-spoke ones) and tubeless tires (although it is not known as yet whether this is a final decision, since the tire manufacturers are not sure that the insert-plugs, which will be supplied to fix flats, will stay in place at the speeds the bike is capable of producing); drew up the engine as a wet-sump to avoid the weight of an oil tank, then designed a dual-function trochoidal oil pump which not only sends lubricant to all moving surfaces but routes it through a small, 4000-calories-per-hour oil cooler mounted below and behind the steering head; decided against turn signal buzzers and self-cancellers, and resisted the appeal of a fuel gauge; adjustable forged aluminum handlebars; forged aluminum footpegs, with their mounts recessed into the support plates for reasons having to do with cornering clearance; originally forged aluminum top motor mounts (which had to be replaced with steel ones when the alloy mounts experienced difficulty with crash tests); a chassis which weighs 29.4 pounds bare; a plastic rear fender, and a plastic seat base.
The battle of the bulge was not fought only on the CBX's ample exterior, but inside the engine as well. The camshafts, for example, are hollow, the clutch is all-aluminum and that mystic motocross substance, magnesium, has finally appeared on a standard street motorcycle. The CBX has a magnesium countershaft sprocket cover, a magnesium alternator housing and cover, a magnesium oil pick-up housing, and a magnesium shift linkage cover.
Irimajiri's struggle against weight brought him into occasional conflict with Otsuka, who would liked to have seen certain components fitted with covers; Irimajiri wasn't going for it. Tip the motor forward, yes; angle the carburetors in, yes, even though in the auricle of his heart that remembered the GP world, he hated to do it; but trade weight for style? Never. Chiseling here, trimming there, examining every component with a fanatic's eye, Irimajiri brought the CBX in under 600 pounds - 599.95, as close as our scales could measure, with the fuel tank filled to the brim and all other fluids in place. In view of the engine's muscle, however, we question his gram-pinching in three areas: the chassis, the front fork pipes (35mm in diameter) and the shock absorbers. Had he allocated a few more pounds here, there is a chance the CBX could have negotiated Willow's Turn Eight full-bore without doing the hippy-hippy shake.
Monday and Tuesday were gone; Wednesday was dyno day. Backing the plain jane refrigerator-white Ford van to the shuttered side door of the dyno room at Webco, the Honda technicians unloaded the CBX and rolled it in. It took the better part of two hours to ready it for the pump, some of which was spent waiting for the NGK representative to bring the nine-series plugs Irimajiri wanted to use. With the bike in place and all calculations done, Webco's Bob Hughes got down to business. By lunch-time we knew how much power the engine made. 85.56 at 9000 rpm, with a 52.27 pounds-feet torque peak at 6500. At 3000 rpm the engine produced 42.50 lbs/ft of torque, going up to 47.1 0 at 3500 rpm and staying over 48 from 4000 all the way to 9000. Horsepower kicked in with authority at 6500 (64.69). At 8000 rpm, fully 1000 rpm below its power peak, the CBX made six horsepower more than the Kawasaki's Zl-R's maximum. By a significant margin, the Six became the strongest stocker ever to pull against the Webco dyno.
Still, Irimajiri had reason to believe that the bike was not doing all it should. The Webco pump was installed so that the company could do meaningful development work on its line of small-displacement aftermarket engine components, and as a consequence, did not have the engine cooling capacity the CBX needed.
"On any multi," Irimajiri explained, "exhaust tuning is crucial. Waves traveling down the pipes have to behave in a certain way if optimum performance is to be obtained. How those waves travel is determined by pipe length, pipe diameter and pipe temperature. If the exhaust system is overheated some of this tuning is lost; I believe that is what is happening here."
Honda, of course, has its own power figures and torque curves. At Asaka the CBX made 103 bhp, measured at the crankshaft. Irimajiri, calculates there to be a 7 per cent power loss between the crank and the output shaft, and another 7 per cent loss between the output shaft and the rear wheel sprocket. Running through the arithmetic, it becomes apparent that under perfect circumstances the CBX should have produced just over 89 bhp on the Webco pump. Additionally, Honda measures the amount of power consumed by frictional losses in its own dynos, and adds that, rightfully enough, to a given engine's output.
Whether it makes 103, 89, or only 85.56, the CBX engine is the Lord High Pumper of all recorded time. Its general layout may seem familiar to anyone who traveled with the European GP circus a decade ago, for it really is little more than a large-displacement, streetified version of Irimajiri's 297cc Six that swept all before it in 1966-1967. But street versions of GP race engines are hardly a dime a dozen, especially if they have six cylinders and 1047cc.
Beneath a one-piece, O-ring-sealed cam cover secured by eight sealed bolts lies much of the CBX's technical other-worldliness. It has not two cams but four, driven by not one chain but two, operating not 12 valves but 24. The first close look sends the hardware junkie staggering from an overdose.
The camshafts are in the normal places. The two exhaust cams, like the two inlets, are joined together by an Oldham coupling. The longer the camshaft the more difficult it is to keep it true during the grinding and heat-treating procedures. The CBX's cams, were they onepiece, would be very long-thus the Oldhams. To avoid the ongoing problem of cam-chain whip caused by oscillations and torque reversals in the crank and the camshafts, Irimajiri decided to use two chains. They are 9.5mm Hy-Vos which, like the primary chain, are manufactured for Honda by Tsubakimoto under license from Morse. The exhaust cam is driven by the crankshaft through a dual sprocket bolted just outboard of the Oldham coupler. The inlet cam is driven by the exhaust cam through the second chain. There are two spring-loaded tensioners: one works against the rear run of the chain from the crank, the other against the lower run of the chain which joins the two cams.
The cams are hollow, made from cast iron; the couplers are nickel-chrome-molybdenum steel. The cams rotate directly on eight cast-in bosses in the head (no bearing inserts are used); the four outboard bearing surfaces and their caps are machined to engage discs on the cam ends to establish positive lateral location.
The inlet valve heads measure 25mm; the exhausts are 22mm in diameter, and the valve length is 89.7mm. The valve heads are stellite-faced, close against sintered iron valve seats and are controlled by conventional inner and outer valve springs which, like all Honda valve springs, are made by Nihon Hatsujo. Valve lash is set exactly the same way you'd see on a KZl000, or a Yamaha 1100, or a Suzuki GS750: with different thickness discs fitted to recesses atop the tappets. On the GP 297 Six, Irimajiri used Winkler caps which went between the underside of the tappet and the top of the valve stem, just like the Kawasaki KZ650Four. "That reduces valve assembly weight," Irimajiri said, "but makes maintenance difficult. We had lots of time between GPs to remove the camshafts and adjust the valves. But with four cams and two cam chains, it didn't make sense on the CBX." Surely he had heard about the Z-l's tendency to spit its shims through the cylinder head at high engine speeds? "That is caused more by valve float than anything else," he said. "Valve float can be restrained by using the lightest valve-train components possible, which was one of the reasons we have a four-valve engine. To see if we would have a problem in this area, we put an engine on the dyno and tested it to failure at 11,000 rpm. We had no problems with the valve train - a cylinder stud broke, after 30 minutes."
The CBX's valves are extremely long, just like the valves in every Honda ever built. The valve length was mandated by an ongoing desire for optimum inlet port angle and shape. The longer the valve the steeper the inlet port's angle of attack can be, and the steeper the angle, the better the flow past the inlet valve head. Inlets and exhausts are inclined 31.30 degrees from the centerline of the bore, for an included valve angle of just under 63 degrees. There are different valve angles for different engines, Irimajiri explained. A greater angle promotes better flow, because in a given engine a wider angle provides room for larger valves. But a narrower angle creates a more compact combustion chamber which, all other things being equal, can lead to more horsepower. In the most general of terms, he went on, valve angle depends on bore-stroke relationships. A short-stroke, wide-bore engine can use a narrow included angle, because the bore dimension provides enough combustion chamber room for acceptably large valves. But a long-stroke, narrow-bore engine would need a greater valve angle to achieve the optimum valve size. Too, he said, there are considerations of proper cylinder head cooling: the narrower the angle, the worse the cooling because there isn't as much room to circulate air across the top of the combustion chamber. "Many, many compromises," he concluded.
The underside of the cylinder head looks for all the world like six XL 250 heads welded together. Combustion chambers are of entirely conventional pentroof design, spark plugs occupy the chambers' dead-centers, and there are flat squish areas to the front and rear. What is unique - and certainly frustrating for Irimajiri - has to do with the wandering relationship between the inlet valve seats and inlet port centerlines. Ideally, the ports - and their carburetors - would be perfectly centered upstream of the inlet valves. That's true of cylinders three and four - the two closest to the middle of the engine - but less true of cylinders two and five, and not true at all of cylinders one and six. Again, this goes back to Otsuka's request for as little carburetor width as possible to provide adequate space for the rider's knees. The inlet ports therefore angle inward. They are also of different lengths: shortest towards the middle, longest out at the ends. This Irimajiri dealt with by filling different-length tubular extensions inside the plenum that feeds air to the carburetors, so as far as the ports are concerned, the distance from atmosphere to valve seat is the same for all cylinders. Even so, he says, some cylinders breathe better than others.
Like the combustion chambers, the pistons are entirely conventional: semi-slipper ART numbers, three rings, flat-topped crowns cut away for valve clearance. They attach to forged steel connecting rods with no small end bushings and ordinary plain bearing big-end inserts. The cylinder casting is a single piece with bore centers 82mm apart and replaceable cast iron liners. A total of 16 studs - of two diameters - secure the cylinder and head to the crankcase.
The crankshaft turns in seven main bearing saddles fitted with insert bearings made of the same material the rods use. Explaining that his biggest problem was controlling the extra-long crank's torsional vibrations, Irimajiri did not elaborate beyond stating that he "had had experience here before." Slightly off-center to the crank's right is the drive sprocket for the exhaust cam; off-center to the left is the massive Hy-Vo that carries power from the crankshaft to Irimajiri's beloved jackshaft, its bottom run partially obscured by a baffle plate and a hydraulic chain tensioner. Pressure for it is tapped directly off the oil pump. At normal engine temperatures the tensioner operates with a pressure of 71 pounds per square inch. Although Hy-Vos are not conventionally in need of tensioners of any kind, this one is necessary to keep the primary chain from rattling around.
The jackshaft - the single component which made it all possible - has a transistorized breakerless ignition fitted to its right end. There are three pulser coils and a timing rotor beneath the chrome outer housing cover; they work with three black boxes mounted deep below the seat, and three dual-lead coils hung under the fuel tank below the chassis' main backbone tube. The coils fire cylinders one and six together, three and four together, and two and five together.
Pointless ignition is now fitted to all high-performance Hondas. It is especially important to the Six, which is in an extremely potent state of tune. According to Irimajiri, over 50 per cent of all engine problems on the 750-series bikes were related directly to the ignition; he could not have that on the CBX, because a bothersome little problem on a tamer engine could amount to a major disaster on the hot-eyed Six. For starting and idling, ignition timing is ten degrees BTDC; at higher engine speeds it is electronically advanced to 42 degrees. The Six is strikingly free of traditional Honda cold-bloodedness. On the chilliest of Willow's chilly mornings it started instantly and was immediately ready for business. We do not know if the same will apply in North Dakota in February; we suspect it will.
Beyond the extent to which individual gears have been lightened, there is nothing apart from brawn to distinguish the CBX's transmission. Both shafts turn on balls or rollers. To quell noise and backlash caused by the gear pair driving the clutch, the drive gear is fitted with a spring-loaded auxiliary gear which carries one more tooth than the main gear. The two gears turn at different speeds, and hold the clutch gear in absolute engagement at all times.
The alternator is not directly linked to the jackshaft; instead, it is driven by a twoplate all-metal clutch, which shields the massive alternator rotor from the engine's frequently violent rates of acceleration and deceleration. The alternator clutch in the test CBX showed excessive wear; the composition of the metals used may be changed on the production bikes.
Irimajiri calls the CBX's carburetors "the most sophisticated ever used on a street-going motorcycle." They have 28mm venturis, are manufactured by Keihin, and were selected to smooth the engine's rate of acceleration. Two features make them unique: an accelerator pump attached to carb number 3 which shares the squirt with the other five through a gallery, and a deceleration, or air cut-off, valve attached to the number one carburetor which also communicates with the rest through a gallery. The purpose of the valve is to prevent backfiring on rapid engine deceleration. The valve in this system closes when intake vacuum reaches a specified level, which shuts off air flow through one of the low-speed jets and promotes a richer mixture.
We have never experienced CV carburetors that work as well as these. They're responsive, vernier-accurate, and they do exactly what Irimajiri says they do: assure smooth engine performance. It has long been claimed by manufacturers that CV carburetors' main reason for being is to isolate the engine from the often-indelicate fist gripping the throttle by allowing the carburetors to decide for themselves what's best for the engine under prevailing conditions. Until now just the opposite has been achieved; CV carburetors, especially those fitted to the larger Yamaha four-strokes, traditionally have made all the wrong decisions and in general have mucked things up. The CBX's, however, are perfect.
Early in the morning on Thursday, the fourth day, it began to rain. The journalists had arranged some exclusive test time at Irwindale Raceway, but 24 hours earlier word had come that Irwindale had been sold to make way for a brewery. Orange County International, the only remaining drag strip in Southern California, was called. Could we bring a certain motorcycle there the next morning for quarter-mile running? Yes. Could security be arranged? Yes, as long as we got there early enough. OCIR was setting up for a motorcycle jumping contest, to be held Friday. Workers were scheduled to arrive at 9:00 a.m. on Thursday; the track would be open, for us, at 7:30.
The journalists arrived at 6:40 a.m.; the CBX, the technicians and the engineers came shortly thereafter, followed by a man with a truck full of straw bales for the jump contest. The tension level escalated sharply. Seven-thirty came and went - no track personnel. The bike, the Honda people, the journalists and a growing number of jump contest workers were still locked outside, searching the sky and staring at their watches. The bike had to run this morning, or not at all - it had to be on an airplane the next day, Friday, for its appointment in Japan. It wasn't raining hard now, but would shortly. Still the gates were locked.
They swung open at 7:50; the track official had been caught in traffic. The journalists and the Honda people poured inside. The rental fee was paid, documents signed, the clocks were turned on and while one of the journalists climbed frantically into his leathers the CBX, still under its cover, was warmed. The journalist, now dressed, sprinted for the starting line and felt the ground. It was wet, which frequently happens when rain comes down. And it was getting wetter.
The journalist ran quickly back to the CBX. The cover was torn off, he mounted up, checked to see that it was warm and rode to the start.
Lining up in the middle of the right lane, engine speed was brought up to 3500 rpm and the clutch was released, The bike sat there, furiously spinning its rear tire and going nowhere. Next the bike was brought to the far right-hand edge of the lane, where there was no rubber build-up. Again engine speed was brought to 3500, and the bike was launched.
Huddled around the starting line speaker, protected by not nearly enough umbrellas, the Japanese heard the first-run numbers: 11.976 seconds at 115.97 mph. The rider brought the CBX off the line at 6500 rpm on the second run. Traction felt all right, considering. The numbers: 11.783 at 116.27. On the third run, starting line engine speed was set at 7500 rpm. The numbers: 11.657 at 116.12 mph.
On the fourth run the clutch got grabby and it became impossible to modulate the engine's power. The testing was terminated and the heavy veils of secrecy slammed back down. By 8:20 a.m. the silky whistle of the Six was replaced by the tapping of workmen's hammers and the peaceful sound of the rain.
Having produced an 11.65-second ET in the wet, no one knew what the CBX could do on a dry track. Three weeks later the bike returned from Japan for the conclusion of its test, and a few hours were set aside for additional quarter-mile running. Once again, it was brought to OCIR. The track was dry; there was a light headwind.
Its first two runs were troubled ones; 600 miles of street riding had sooted-up its spark plugs, and the engine was not pulling hard in the upper gears. Action Fours, a high-performance aftermarket manufacturer, was called, and Action's Jim Dickinson brought six new NGK D8s down to the track. The CBX's subsequent runs were as follows: 11.80 @ 116.73; 11.55 @ 117.49; 11.64 @ 116.88; 11.63 @ 116.73; 11.65 @ 116.88; 11.58 @ 117.18; 11.57 @ 117.49; 11.62 @ 117.18; and 11.61 @ 116.58.
The bike's 11.55-second ET was by almost two-tenths the quickest quarter-mile ever turned by a standard production motorcycle tested by any magazine; its top-end blast of 117.49 was more than two miles per hour up on the XS Eleven's fastest. There is no doubt: the CBX Six is the hardest-accelerating production vehicle ever built.
Race tracks are solemn places. They segregate, and then totally ignore, anything which has no direct bearing on speed. Thus far the journalists had ridden the CBX only on race tracks. When it came back to us early in December the initial dealer meeting was over, and the security was lifted. Finally, we could experience the Six in its proper environment: the street.
It becomes immediately obvious that the bike's street behavior is in many ways antithetical to its race track behavior; areas of marginal weakness on the track become areas of specific strength on the street. It also becomes immediately obvious that as a sporting street motorcycle the CBX is unmatched. Fact: the Six has more cornering clearance than any medium- to large- displacement motorcycle we've tested in the past five years-better than any standard Ducati, or Triumph, or Suzuki, or Yamaha, or Kawasaki, or Honda, or anything - this despite its 23.4-inch engine width dimension. Fact: the bike can accelerate uphill from 15 mph in fifth gear without a hitch, or a stumble, or a cough or a shudder, and can give an excellent account of itself in high-gear roll-ons from 50 or 55 mph - this despite the engine's hotsy-totsy state of tune. Fact: on California's twisting mountain roads the bike is as agile and accurate as motorcycles weighing 150 pounds less. Fact: it has the smoothest clutch operation and the cleanest gearbox we've experienced since the 750 Ducati Super Sport. Fact: despite its heady retinue of cylinders and pistons, the CBX above 6000 rpm vibrates barely less than a GS1000 Suzuki and more than a Honda GL1000 or Yamaha XS Eleven. It obviously vibrated on the track as well - we just hadn't noticed. Fact: despite the flimsy dimensions of its swing arm and pivot pin, its 35mm fork pipes and its ordinary-looking FVQ shocks, it is virtually impossible to induce wallowing or wobbling in high-speed street cornering. Among big multi-cylinder bikes, only the GS1000 handles better at speed - barely.
This is a sport motorcycle. Because Honda offers a GL1000 for touring, the CBX makes no concessions to the long-distance crowd. This becomes apparent after the first 200 miles of highway travel. The front fork springs are stiff: 44.7 lbs/in initially, then 55.9 lbs/in when the second rate takes over. The rear springs are likewise - 112 lbs/in - and while the fork acknowledges freeway expansion joints, the shocks do not. On the open road the ride could be described as firm only by the most charitable of testers. Everyone else would call it severe. The ride is matched by the saddle. You put your fanny where the Six wants you to put it - in the depression between the front of the seat and the riser in the middle. There is less room here than meets the eye, and what room there is is stiffly padded.
Yet if the seat were any other way, it would be inconsistent with the rest of the bike. There is nothing soft about the CBX; it is positive in everything it does. It turns decisively, accelerates decisively, stops decisively, shifts decisively. Even the hand-switches are positively detented. But freeway comfort aside, in none of its systems can there be found harshness or crudeness. The clutch engages with such unwrinkled control and the carburetion responds with such accuracy that the bike cannot leave a stop sign with anything but supreme grace. The transmission can be faintly clunky if it is called upon to maneuver between first and second gears at low speeds, but if the rider's inputs are resolute the gearbox flows through its closely-spaced ratios with a suppleness that's almost hydraulic.
Away from the race track one can explore the full range of the engine. When it's cold it idles at 250 rpm; when it's hot it idles at 700. Beyond a sound like sewing machines in a padded room, the six-cylinder produces no low-speed mechanical noise. Quarter-mile times and dynamometer figures notwithstanding, the CBX is as sweet in heavy traffic as any motorcycle has ever been. It never coughs and dies, even if you jerk the carbs wide-open when the engine is idling. The low seat height, light-touch brakes, the total absence of drive-line snatch and the character of the clutch mean the rider can maneuver through the most grinding traffic snarl with delicacy.
But lean on the engine and it'll give you all you can stand. It doesn't have the seven-liter midrange power of the Yamaha XS Eleven; it won't take you by surprise and get you in over your head, because the CBX engine communicates while the XS engine isolates. If the XS is a Rolls Royce with a blown Chrysler hemi motor, then the CBX is a Formula One car with a license plate. The big Yamaha gathers speed with lethal deception; the Honda hits 6000 rpm and begins to erupt. When you reach that part of the Six's powerband where serious business is done, you know it. You cannot escape from it; above 6000 rpm the engine makes no effort to deny its heritage.
Some observations about details: careful as the Honda designers were with the CBX's instrument layout, and as charming as it is to discover that the speedometer needle glows in the dark, it doesn't work as well as it should for nighttime riding. The red numerals on the speedo and tach are difficult to see, and the high-beam indicator light is so intense as to be a real distraction.
At normal highway cruising speeds the engine produces an interesting mix of mysterious noises. At 50 mph there is a muted warbling that might come from the primary drive gear pair; between 65 and 70 mph there is a high-pitched, chirping squeal that probably emanates from the alternator drive clutch. Enveloping all is the bike's medium-level inlet whistle, and the gentle honk of the tailpipes.
The big Honda was ridden by six staff members, all of different dimension. All felt the CBX has the most comfortable seating position (not the same thing as a comfortable seat) they had ever experienced. The slightly rear-set footpegs, the width and height of the handlebars and the way the saddle positively locates the rider all result in a wonderfully stable operations platform from which to lead the orchestra.
The CBX is a mountain road flyer beyond anyone's wildest dreams. It swivels down low-speed twisties like the most well-bred middleweight and carves through the fast stuff with only an infrequent trace of the flutters. It is the first bike in memory which completed its street testing without so much as a single pavement scratch anywhere on its undercarriage - and the shock springs were never changed from their full-soft setting.
The bike's extraordinary cornering clearance means many things: you can turn the bike quickly without worrying that the suspension will overmush and cause something hard to bang against the pavement and set off a wobble; bumps in the middle of high-angle turns do not result in the kind of road contact that unloads the rear tire; and if the back tire does slip when too much power is applied exiting a turn, there is enough cornering clearance left to salvage the situation. Throughout our mountain road testing the CBX remained a total delight. Braking deep into turns doesn't rankle it; mid-corner corrections are accepted with equanimity; the rider always finds himself in the right gear, and at the right engine speed, on a bike with which he can be intimate. Above all, it is this feeling of intimacy which sets the CBX apart. It is all there all the time; it is taut, solid, together and distinctly European in flavor. Nothing about the bike is clumsy or strident. There are no significant loose ends; it is uncompromised and utterly self-assured, and it is the most exotic, charismatic motorcycle we have ever tested.
The CBX-Six was conceptualized to be a function-intensive motorcycle which, due directly to the existence of the GL1000, could be tightly focused on a relatively small number of design objectives: handling, braking, acceleration, engine smoothness, and comfort within the boundaries established by the primary performance goals. It is not the best standard production race track handler around - the GS1000 Suzuki is - and it does not have the world's greatest highway ride quality. Its 35 mpg fuel consumption rate is inferior to most motorcycles and many automobiles, and when the time comes for your dealer to adjust those 24 valves or re-synchronize six carburetors, your wallet will cry out for a transfusion. Count on replacing rear tires frequently; count on paying close attention to the bike's #630 rear chain. The CBX rubs hard against the acceptable limits of mechanical intricacy and weight, and anyone with a pragmatic view would take issue with both the bike's complexity and its total performance concept.
But the Six was not built for pragmatists. It was built for romantics, for people with soft spots in their hearts for mechanical maximum expressions, for people whose specific reasons for motorcycling match the CBX's specific reasons for being built. Its European texture is a breakthrough for the Japanese motorcycle industry. Its engine performance is devastating, its high-speed handling and cornering clearance are remarkable, its drive-line character is unflawed and the linear responsiveness of every control and system is unique in all of motorcycling. It cannot be rationally compared to anything on the street, because nothing except a GP road racer is as narrowly committed to high-speed performance.
It embodies extravagance without vulgarity and high style without pretense - you see muscles and tendons, not chrome and fussiness. It has been designed, not decorated. There is no trashiness in the concept, and none in the execution. The CBX is an immensely flattering bike with perfect elegance and total class, and history will rank it with those rare and precious motorcycles which will never, ever be forgotten.
Source Cycle Magazine1978