Honda redefines the 250
There was very little wrong with the C72 Honda that appeared in 1959 – “a machine of almost unbelievable sophistication” according to the British press – but what followed was a whole lot better.
In designing the CB72 (and its bigger-bore brother, the 305cc CB77), Honda’s engineers considered the functionality of every existing component before deciding on the final specification.
Labelled “the star of the show” when it made its European debut at the Amsterdam Show, the C72 was the logical derivative of the C70 Dream from 1957. The C70, with its pressed steel frame, forks, swinging arm and mudguards had been rarely seen in the west, Honda exporting just 285 machines that year, mainly to South East Asia. The C70 was updated in 1958 with the addition of an electric starter, and in C71 form, arrived in Britain in 1958 equipped with 6 volt electrics. The new C72, with 12 volt electrics, the C92 Benly 125 and the C100 step-through, formed the basis of Honda’s export drive into Europe and USA, but although the specification of all three was brilliant for the time, the styling still polarised opinion. And so it was that the CB72 came into being – incorporating the excellent SOHC Twin cylinder 250cc engine, but with more conventional styling, including a tubular steel frame. The original C70 engine redrew the battle lines in the quarter litre class. Development of the European 250s from the likes of Moto Guzzi, MV Agusta, NSU, Maico and the Eastern Bloc CZs and Jawas had largely stalled as cheap cars became more readily available. In the case of NSU and DKW, they simply ceased making motorcycles altogether. In England, BSA, AJS/Matchless and Ariel had venerable 250 singles, Ariel would soon have the twin-cylinder two-stroke Arrow, and Norton fiddled about with their Jubilee twin, but beneath the surface, there was little new. And that’s largely because the bean counters had declared the class all-but dead, and not worth the investment for tooling to produce new models. Not so the Japanese. Having started with tiddlers, the only way was up, and their home market was a fertile one for such machines. The C70’s engine was – uniquely for the period – all alloy, with horizontally split crankcases and dry sump lubrication. Vitally, the electrical system of the little twin was well thought out and reliable – almost the complete antithesis of most of its rivals. But there was still the matter of the very Japanese styling, which at the time was characterised by squared off panels and sharply angular design.
In designing the CB72 (and its bigger-bore brother, the 305cc CB77), Honda’s engineers considered the functionality of every existing component before deciding on the final specification. By the time the model went into production, it shared virtually nothing with the C70 line apart from a general similarity in the powerplant. The CB72 engine became wet sump, with a 180º crankshaft instead of 360º - the crank running on four bearings, outer ball bearings and roller inners. The single overhead camshaft was chain-driven from the centre of the crankshaft. Aluminium alloy was still used top to bottom, but inside the cylinder head, the combustion chamber employed a cast iron “skull” as used on the factory’s highly successful racers, with the valve seats cut into the skull. A fairly high 10.0:1 compression ratio tested the quality of the fuel of the day, and twin 24mm Keihin carburettors fed the mixture via two paper air filter elements. A four-speed gearbox, naturally built inunit with the engine and driven via a single-row chain from the left side of the engine, should have been quite adequate but due to an extremely odd choice of ratios, was perhaps the weak point of the whole design. First gear, at 18.63:1 was extremely low, with a wide gap to the 11.10 second gear. This meant second was often too tall for use in traffic, but bottom was too low. Also, when changing back through the gears, shifting from second to first almost threw the rider over the handlebars. A similar situation occurred with the later 4-speed CB450, but this was cured by adding a fifth ratio between first and second – a remedy that was never applied to the CB72. Nowadays, NOVA in Britain offer a five-speed transmission for the CB72/77 that goes straight in and reportedly transforms the performance. Gone was much of the pressed steel, with a tubular steel frame and swinging arm. The frame was of the
spine type, using the engine/gearbox as a fully stressed member. The old leading link forks were also dispensed with in favour of conventional looking telescopics, with similar Brit-styled spring/dampers, adjustable for spring pre-load, at the rear. Mudguards were very British in appearance; the front a neat ‘three inch’ blade with twin stays, and the rear a stubby but adequate job with a screwed on horizontal mudflap. The C70 seat design, with its featured curves and contours, also gave way to a much more conventional, flat-topped style, still with a centre grab-strap and a neat lower chrome trim strip.
The flat-sided fuel tank set a styling trend that Honda would follow for the next few years in a variety of models, with screwed on chrome side panels and extensive rubber knee pads. A large headlamp with 35/35w illumination sat up front, with the combined speedo tacho instrument set into a cowling incorporated within the headlamp shell. Although similar to the earlier items, the CB72’s brakes were all-new; both front and rear being 8-inch twin leading shoe. Both the CB72 and CB77 were available in three basic colours; black, red or blue, with silver for the mudguards and air filter side covers. One British road test described the CB72 as “a difficult bike to ride; no machine for the novice. To be kept going quickly on an ordinary road, the rider needs to keep the rev-counter needle pointing between 7,000 and 8,000 rpm, and to change gear much more often than usual.” The fuel consumption (62 mpg) also came in for some criticism, but praise was universal for the handling and braking. Later, Honda introduced a 360º crankshaft for the CB72, this model were known as Type 2, and identified as such by the inscription on the right side camshaft cover. Although listed as having the same power output, the Type 2 produced a wider spread of power with increased torque. As well as being sold extensively in the US, the Type 2 engines were fitted to Police model CB72s (the CYP72) sold through Asia, presumably for their ability to handle low speed traffic better.
The need for speed
Honda obviously saw racing potential in the CB72 (or at least, café racer hot-up), as provision was made to easily convert the standard footrest/brake/gear lever to ‘rear-set’ configuration. A large cast-alloy bracket on each side acted as the muffler mounting point and contained a central boss to move the footrest 60mm to the rear, and both the rear brake and gear lever linkages could be substituted for longer versions to suit. This footrest/lever set up meant that there was no room for the kick starter to rotate in the conventional fashion, so it was a case of pushing the lever forwards – a technique not that difficult to master but fortunately not called for often due to the reliability of the electric starter. Honda was riding a wave of racing success in the early 1960s, and was naturally keen to exploit this success in its road models. The CB72 could be had, in Britain at least, with flat handlebars, bigger bore Keihin carburettors, a slightly warmer camshaft and the rear-sets. A number of accessory firms offered racing-style seats. The factory even produced a very limited number of genuine racing CB72s, code named CYB, which looked similar to the RC61 from a distance, with the same elongated fuel tank and seat. In fact, they employed more than 100 different parts to the road bike, including alloy rims, footrests that could be mounted in three different positions, clip-on handlebars with cables to suit, two styles of reverse cone megaphone in different tapers, alloy mudguards, two-way damped rear shock absorbers and lots of other smaller bits and pieces. Inside the engine was a racing camshaft, valve springs, higher-spec primary chain, close ratio four-speed gear cluster (with a fivespeed also listed), racing carburettors and different castings to replace the stator and starter motor. The CYB conversion was actually marketed as a kit in several forms, from basic to a complete set up. From all accounts, the racing CB72s were not particularly successful, although they were capable of running at 11 – 12,000 rpm. Problems with the camshaft drive, manifesting itself in broken cam chains (usually the connecting link) plagued the models, and it was only when “Pos” Yoshimura worked his magic inside the engine that a degree of success was achieved. A handful of CR72 and CR77 racers were sold to selected riders, including Irishman Tommy Robb and South African Bruce Beale. These used gear drive to twin overhead camshafts, with one-piece four valve heads, six speed gearboxes and a dry clutch. The cylinders were separate, with the camshaft drive gears between them in a compartment sealed
with a rubber gasket. The 54mm x 54mm 250 produced 42 horsepower at 12,000 rpm, while the 60mm x 54mm 305 developed 46 hp at 11,000 rpm. Robb’s CR77 was timed at the TT at 134 mph – 2 mph faster than Mike Hailwood’s works 350 MV Agusta. In Australia, the CB72 quickly became the weapon of choice for the booming Production Racing scene. When Lightweight (250cc) and Unlimited Production races were introduced at Bathurst in 1962 (after years of concentrated lobbying for ‘clubmen’ who had little hope of getting onto the grid otherwise), the CB72 dominated the entry and took the first three places ; Gary Gates winning from Victorians Ray Moloney and Ron Bridgeman. Maloney won in 1963, and it was Terry Dennehy’s turn in 1964, but after that, the two stroke brigade, in the shape of Yamaha’s YDS-3 took over, and this pretty much mirrored the fortunes of the CB72 world wide. The CB72 was under threat from two strokes, not just on the track, but for road sales, Honda waging a single handed war against the Yamaha YDS-3, the six-speed Suzuki T20, and Kawasaki’s new A1 discvalve twin. Honda maintained, quite correctly, that the majority of the sales in this category (and in 350cc) were to be had in the commuter, not the sports segment. Sales of the CB72 were in steep decline by 1966, and the following year Honda showed its replacement, the five-speed CB250 with a totally new powerplant. The new model was slightly heavier, slower, but a more refined package, and in 350cc form as the CB350, became the highest selling full sized motorcycle in the world, thanks to the massive take up in USA.
In the saddle
In mid winter 2014, I was fortunate to be loaned the featured CB72 by owner Richard Steain, for use in the annual Debenham Rally in the NSW Southern Highlands. I actually owned and restored a CB72 myself many years ago, but when I put the machine on the road I found it less than wonderful. The main problem was the curious spacing of the gearbox ratios, as previously mentioned. In Sydney traffic, it was also a bit of a chore keeping the engine buzzing in its comfort zone, but the handling was very good, as were the brakes. Twenty years after that experience, the day blasting between Bowral, Mittagong and other small towns in one of the prettiest regions of NSW was an altogether different experience. Richard Steain is a man highly versed in the smaller Japanese bikes, and (with twin brother John) was a formidable talent on the race tracks. His tackle then was mainly T20 and T250 Suzukis in the rough and tumble world of Lightweight Production racing, but in latter years he has collected and restored a nice line up of Japanese bikes, mainly Hondas, of various sizes. His CB72 is not pristine, but it is very well put together and is a joy to ride. On the open roads, I didn’t even mind the gear ratios too much – I just revelled in the little machine’s agility to swoop through the twists and turns. I even remarked to John that the handling was ‘Velocette-like” – the highest praise I can bestow! There is increasing emphasis on the smaller Japanese bikes as rally transport, and with good reason. They’re light, responsive, handle well and require minimal maintenance. The CB72, with its push-button starting, is an excellent choice and prices are still reasonable.
Getting dirty (but only a little)
USA quickly warmed to the CB72, (particularly after Elvis Presley hit the screens in the 1964 movie Roustabout where he rode a CB77) but became much more enthusiastic to the concept with the release of the ‘street scrambler ‘ CL72/CL77. These models used the basic CB72 engine package, but the frame was beefed up with the inclusion of a single front downtube, splitting into a cradle under the engine. This mod necessitated the removal of the electric starter, which on the CB72 was mounted at the front of the engine. This really did not present a problem, as the engine was easily kick started, especially as the kick starter now rotated in the traditional pattern, rather than the ‘forward’ motion of the CB72. Wheels on the CL models grew from 18-inch to 19, and a hydraulic steering damper was fitted as standard. Perhaps in search of more low-down torque, the 24mm Keihin carbs were replaced by 22mm Biliaths. When the 305cc CL77 came on board for 1965 (in the US), it sported 26mm Keihin carbs. The twin-leading shoe brake plates became single leading shoe front and rear on the CLs. In reality, these street scramblers were better at boulevard posing than any form of rough stuff, but the styling, with the high-mounted exhaust system on the left protected by an elaborate heat shield, the small fuel tank, high handlebars and abbreviated mudguards certainly captured the imagination of the buying public and the CLs sold in big numbers. Late in the production run, the CL was released with a 360º firing order. In USA, sales of the CL77 far outstripped that of the 250 and both the CL models enjoyed good sales in Japan.
A red 1966 model CB72 restored by Steve Ashkenazi. A blue CB72 restored byCampbell Classics.
BELOW Allan Osborne at Calder in February 1962 on a CB72 that has been race-modified with clip-ons, rear sets, megaphone exhausts and with the stator and other weighty bits removed. LEFT Original Honda brochure showing the three colour options for the CB77.
At Darley in June 1962, P. Mills (10) on a new CB72 leans on Norton-mounted P. Morgan.
Top Victorian rider Ray Moloney, winner at Bathurst in 1963, on his brand newCB72 at Darley in June 1962.
Slab-sided fuel tank with traditional knee rubbers.
TOP A distinctive and attractive engine design – Laverda certainly thought so! ABOVE 24mm Keihin carburettors. BELOW Type 1 on the camshaft covers denotes the 180º crankshaft engine. BOTTOM Starter motor sits neatly at the front of the engine on the CB72, but was eliminated on CL models. BELOW RIGHT Alloy brackets on both sides have a centre boss for rear-mounting footrests. BOTTOM RIGHT Typically ‘sixties Japanese, the headlight-mounted instrument combines the tacho and speedo.