Honda CB750, CB900, and CB1100 - CLASSICS REMEMBERED

Last call for air cooling

1979 Honda CB750F studio side view
1979 Honda CB750FCourtesy of Honda

After Dick Mann's 1970 Daytona win on the new CB750, US Honda lovers had little to celebrate in racing. Honda, having established their brand worldwide, seemed to settle into a General Motors-like attitude of sales supremacy (oddly, GM had 53% of the US market back then, but more like 23% today).

“Racing? Why would we bother with such nonsense?”

It was the Age of Iron Bikes – conservative design, heavy chassis and engines, attractive styling, affordable mass-market prices. Not such a bad combo. And yet… where was the electric excitement of Honda’s 1960s Grand Prix bikes? Honda fours, fives, and sixes, revving as high as 19,000? Those were intoxicating days.

Honda CR750 racebike static side view
Honda CR750, one of four factory-prepared racers for the 1970 Daytona 200 race, based on the then-new CB750 roadster. This bike, ridden to victory by Dick Mann, is on display at Le Musée Auto Moto Vélo, a transportation Museum in Châtellerault, France.By kinsarvik, via Wikimedia Commons

Honda’s return was gradual, and took an unusual path – European endurance racing. The company built about ten RCB1000s, the engine loosely based on the original air-cooled CB750 of 1969, but now with DOHC instead of single-cam-and-rockers, and driving its gearbox through an idler gear rather than the CB’s path-breaking automotive-style silent chain.

While this special bike (115-hp @ 9500) was cleaning up in endurance (won everything in 1976), a decision was being made to spend major resources on a revolutionary 4-stroke Grand Prix bike, the oval-piston NR500. The organization created for the task came to be known as the “NR-Block”, and would become a powerful political entity within Honda, fostering a generation of V4 production bikes.

NR500 oval pistons details
The NR500's main moving parts. Each oval piston is served by eight valves and two spark plugs, moved by two connecting-rods. Designed to overturn the two-stroke applecart in 500 GP racing, it never scored a single GP point. Planned to peak at 23,000, the most its piston metallurgy would permit was 19,000, allowing a late version to make 136-hp. Freddie Spencer said, "It didn't have a powerband - it just revved." Another of its riders, Mick Grant, said it was "heavy as lead" - not surprising considering the mass of metal needed to reliably contain all its whirling violence.By the original uploader was Ux z at Japanese Wikipedia, via Wikimedia Commons

But old-timey air-cooled in-line fours weren't dead yet; Honda decided to recover some of the hi-po market share that had been lost to Kawasaki (Z1), Suzuki (GS series), and later, Yamaha (XS11). DOHC and four valves had made an endurance winner of Honda's original in-line, so why not release a production version of the engine that had humbled the other makers' endurance entries? The result was CB750F of 1979, with fresh styling (72-hp), followed in Europe by CB900 of 1981 (84-hp), and then CB1100 at 108-hp.

In the US, Honda dived into US Superbike and AMA Formula 1 (which pitted one-liter four-strokes against the existing 750 two-strokes such as Yamaha TZ750). The race shop at American Honda was put on a war footing and titanium valves and con-rods were ordered by the case, in $12,000 lots. Cylinder heads were trucked out to the top airflow shops such as Branch Flowmetrics, Valley Head Service, and Kinetic Analysis. The plan was to get everything moving in parallel to save time that could then be used for testing and development before the season began. Fast-talking rider-impresario Steve McLaughlin (who would later talk the World into World Superbike) was issuing orders. Top people were summoned to become a racing department, among them Udo Gietl and fabricator Todd Schuster, from the old BMW racing group.

Honda CB750F Ten Best Oct 1979 magazine layout
Honda CB750F Ten Best Bikes of 1979 from the October 1979 issue of Cycle WorldCycle World

Before the drumbeat of all this action marches us away, we remember that Wes Cooley was AMA Supers champ in 1980, and that Eddie Lawson took it on Rob Muzzy Kawasakis in 1981 and '82, followed by Wayne Rainey (again on Muzzy Kaw) topping the first year of the new 750 Superbike engine displacement. This was not an easy hierarchy to break into.

CB750F was a transitional motorcycle, for unknown to us outsiders, Honda’s R&D shops were now prototyping what would become the somewhat ponderous VF750S ‘Sabre’ liquid-cooled V4 production bike of 1982, then the revolutionary 750 Interceptor Superbike of 1983, which sold out as word-of-mouth spread the word about its fabulous handling.

But back to CB750F. The original endurance-racing RCB1000 (bore & stroke 68 x 64.8 = 941.3-cc) drove by central gear, through an idler, to the gearbox countershaft. This was a departure from the original silent chain primary of the 1969 CB750 production bike, but like it, the result of lining-up so many side-by-side shafts was quite a long engine. When the RCB concept took new form as the production CB750F, it was back to silent chain.

Honda CB750F Road Test Nov 1979 magazine layout
Honda CB750F Road Test from the November 1979 issue of Cycle WorldCycle World

Remember that while Kawasaki and Suzuki big-bikes of the 1970s had traditional multi-piece, pressed-together rolling bearing cranks, Honda had pioneered the “automotive solution” in the 1969 CB750 – a stiff forged one-piece crank spinning in pressure-lubricated insert-type plain bearings. This in turn required split-and-bolted connecting-rods. These cost-cutting and durability-enhancing features were carried forward to the new CB in-lines. Unfortunately wheelbase ended up long – nearly 59 inches. This is a problem in racing because;

  1. Wheelbase is the "lever" by which the front wheel steers the whole vehicle. The longer the wheelbase, the longer it takes to change direction.
  2. When braking or accelerating, it is essential for tire grip to achieve prompt weight transfer to front or rear tire respectively. The longer the wheelbase (or the lower the CG) the more difficult it is to achieve such rapid weight transfer (look at how high the engines are in Honda MotoGP bikes).

In making Superbikes or AMA F1 bikes from these late CBs it was essential to speed up their steering by all possible means. Reducing the steering-head angle pulled the front tire back about an inch, and the lower gyro resistance of a smaller 16” front wheel was another possibility. Stiffer, larger-diameter fork legs from Gold Wing were held in special machined-from-solid fork crowns.

The production bikes had 19" front/18" rear wheel sizes, shod with tall tires. The result was traditional massive rubber-and-steel gyroscopes, at all times opposing the efforts of the rider to change direction. At the time, this was normal – the way bikes had always been (nearly all British Twins had used 19" fronts). But complete change was coming. Who could have predicted that the Honda Interceptor of 1983, built in small numbers as a "homologation special" just to legalize its use in AMA racing, would sell out instantly because of its handling? Americans cared only for quarter-mile time and top speed – everyone "knew" that. Yet suddenly, public taste took a new direction. The result would be the long-running Era of the Sportbike, which has declined so steeply after 2009.

Cycle World March 1980 magazine cover
Honda CB900 on the cover of March 1980 issue of Cycle WorldCycle World

Slick, low-profile tubeless racing tires and lightweight cast magnesium wheels also did a lot to trim those massive gyroscopes and speed up handling.

Many, many engines were built and tested in American Honda’s return to racing. Larry Worrell (aka “Mississippi Round Man) described a family of three different bore/strokes, based upon the 750 crank, the 900 crank, and perhaps the 64.8-mm stroke of the RCB. Combustion was quickest in the smallest of the three bores because;

  1. Flame travel distance was a bit smaller and;
  2. Greater clearance between piston and head gave turbulence room to persist longer.

Naturally, the shorter the time occupied by combustion, the less heat is driven into combustion chamber and piston crown. But in the end, the overriding need is for higher rpm, to perform the power-producing cycle more times per minute. This dictated use of shorter stroke, larger bore, and their result, slowed combustion. The last of the air-cooled Honda Supers (1982) supposedly used the 62-mm stroke of the CB750F.

In the 1982 Daytona Superbike race Hondas took the first three places, but only after a strong challenge from Eddie Lawson on the Muzzy Kawasaki (late in the event he sat up, going slow). Yet earlier that week such a brilliant result looked impossible. In practice, one after another of the hastily-engineered Honda engines made the fateful crunch (sounding like someone stepping on a giant cockroach) that indicated an engine wreck – until all their engines were gone. One I witnessed, accelerating from turn one. It popped, its rider braked and ran off onto the grass outside two. He parked the bike against the fence there and began trotting back for another so as not to waste practice time.

Daytona Superbike story layout from Jun 82 Cycle World magazine
Daytona '82 Superbike Race from the June 1982 issue of Cycle WorldCycle World

On Wednesday of that week (which in that time was "Sportsman day"), build stands were set up outside the Honda garage in full sunshine, as the crew set about building fresh engines from parts. Try to imagine the inventory! No knocking-off at five on this day. New team manager Ron Murakami presided, looking rather like a distinguished doctor (Had previous manager Steve McLaughlin ordered too many titanium parts? Had he uttered too many words?).

In photographs from that week we can clearly see the big oil cooler beneath the front number plate, served by giant stainless armor braid lines. There too can be seen the electronics boxes of the German-made Krober ignition. Weak ignition had been a feature of the CB race kits – often unable to jump gaps much greater than .014”! The simple Krober, with only 1/6 the total spark energy of a modern automotive system, made that deficit good. Also in the picture are the 7-spoke wheels of mag wheel pioneer Elliott Morris. Also lay-down inverted twin rear shocks (the long-travel suspension revolution began in 1974) and extensively drilled brake discs.

When in 2000 an ex-team bike owned by Rollin Lofdahl was run around Willow Springs in California by Freddie Spencer, it displayed a high fluttery idle and its proper growly sound, accelerating. The year 1982 was also the year of the Honda FWS, a 1000-cc racer for AMA's F1 class, which had inherited from the NR500 its slipper clutch. No such clutch on the CB! It dragged its rear tire and chattered, even though Freddie was being very careful (At Charlotte in 1982 his bike had blooched its filter and blown out all its oil).

What happened to FWS? It may have been another victim of Honda’s accelerated return to racing. Spencer and Baldwin were able to set the pace but such powerful bikes went through tires at a fearful rate. Winning the Daytona 200 was Graeme Crosby, on a same-old same-old 0W-31 (factory Yamaha TZ750 of the basic type that had won every 200 since 1974).

Daytona 200 story layout from Jun 82 Cycle World magazine
1982 Daytona 200 Race from the June 1982 issue of Cycle WorldCycle World

When you close the throttle on a big four-stroke engine at high revs, it takes a lot to keep it spinning – more than the rear tire, partially unloaded by braking weight transfer, can muster. This is engine braking. So the rear tire drags and hops. The handiest “cure”? That “high fluttery idle” was no accident; setting the idle at 2000-rpm killed a lot of the engine braking, making corner entry less exciting. Thirty-five years later, on-board electronics would civilize this problem.

Do I hear the jingle of plates in a dry clutch? Yes, these bikes were given dry clutches from AHM Special Products that were less likely to drag their riders forward before the start dropped. On the track, their metallic friction material got hot enough to grip, but in dyno testing, clutch slip could be a problem.

The eventual result was 145-hp, safe to 12,000.

So what’s the bottom line? These giant air-cooled Superbikes were the last of their line, and arrived just as Honda was awakening from its Big Sleep. So they received big helpings of technology that would soon re-establish Honda as a giant in racing. But it would at first all happen too fast to be consistently successful.

Not long before, the NR oval piston bike had been retired without having won a single GP point. As Mike Baldwin told it, the MX division within Honda had then stood up and shouted, "Coach! Coach! Put me in – I know I can score!." Engineer Shin'ichi Miyakoshi had seen 250s come close to the lap times of the 500s at Assen, in Holland. He also knew that the biggest problem facing the 130-150-hp 500s was tire durability.

“What if we build a 100-hp 250?” he asked himself. It would be light and maneuverable, yet demand less from its tires.

When the first NS500 Honda two-stroke Triple entered GP racing in 1982, it developed just 108-hp @ 11,000. Its rider, Freddie Spencer, already knew how to ride a 250 with a narrow 1200-rpm power band. He won for the first time in Belgium that year, and was World Champion the next year.

In this super-intense period Honda had a lot of balls in the air, and was able through impatient persistence and massive outpouring of resources to achieve success. The late CB fours were just one tool in their kit. Looking at them today, they have a kind of dated majesty, making me think of actor Robert Mitchum, late in his career.

Honda NS500 static 3/4 view
When the NR was unable to put Honda back on top in GP racing, they turned from complexity to simplicity with this NS3 two-stroke Triple, with seven motocross-inspired moving parts (crank, three rods, and three pistons). Based on engineer Shin'ich Miyakoshi's idea of a bike as light and handy as a 250, but with 100-hp, the NS in Freddie Spencer's hands won a GP in its first season and the 500 championship the year after, 1982.By Rainmaker47 (Own work) [CC BY-SA 3.0], via Wikimedia Commons