Twin PEAKS

Competition for the quickest aircooled 250cc twin in the Seventies reached its peak when Yamaha launched the ‘race developed’ RD series. John Nutting charts its progress.
IT’S not so often you hear these days a road tester saying that he liked a bike so much he went out and bought one. There’s such an extravagant supply of test bikes that they’d rarely get the chance to ride their own bikes anyway.
A quarter of a century ago or more it wasn’t quite the same. The manufacturers, few of which by then were British, were peculiarly tight with demonstration machines and only grudgingly accepted the value of publicity in magazines. Partly this was because importers were often not wholly-owned subsidiaries of the manufacturers.
An exception was Mitsui Machinery Sales, the Yamaha importer in the Sixties and Seventies, who were happy to provide a string of models for the leading publications to write about.
As a wet-behind-the-ears tester for Motor Cycle, the weekly paper, my first Yamaha test bike in the summer of 1972 was an XS650 four stroke twin, followed by a 200cc CS5E 200cc twin and its later RD200 version.
Even better was the RD250 two stroke twin which left such a lasting impression on me that when the test bike had completed its duties I bought it from Mitsui and pressed it into a new role as a production race bike.
The RD series that appeared in the UK in 1973 represented a turning point in Yamaha’s model range. Although it followed a design theme that could be traced back to Yamaha’s twins of the Sixties, the RDs were redesigns with common features for both the 250cc and 350cc versions. Both aircooled twins, they used, for the first time, reed-controlled inlet ports, a feature that provided more flexibility and smoother throttle response.
As such, they were a step-change in a technology battle that had been waged between the four Japanese manufacturers in the 250cc and 350cc classes. Yamaha’s first 250cc twin, which looked remarkably similar to a German Adler, appeared in 1958 with a modest 14.5 bhp, but the following year it spawned the sportier YDS-1 with 20 bhp. At the time, Honda’s brilliant CB72 ohc twin offered a claimed 24 bhp.
By 1964, Yamaha’s YDS-3 had caught up, and then Suzuki pitched in with its T20, a six-speed model with 25 bhp at 8000 rpm. Both were eclipsed however when, in 1966, Kawasaki launched its A1 twin that, with disc valve porting, punched out 31 bhp. Honda answered in 1968 with a new CB250 boasting 30 bhp at 10,500 rpm.
The downside of this power race was peaky and awkward engines. This was less of a problem with Yamaha’s phenomenal racing TD and TR series which used tuned versions of the road engines in lightweight frames. But the engine designs also had their limitations, the most debilitating of which was their crankshaft mounted clutch, which limited revs and compromised reliability.
So for 1970 Yamaha brought out its new twin with horizontally split cases, more sophisticated cylinder porting and reed valves, the so-called Torque Induction. The first, called the DX250, appeared in Japan and like the previous year’s model used a 2LS drum front brake. This was followed in 1972 with the DX250 Pro featuring 30 bhp and a disc brake.
In parallel, the production racers were being revamped and for 1973 the first watercooled TZ versions were offered. The only features in common with the road bikes were the engine cases, but that was sufficient justification to call the road bikes for that year the RD (race developed) series for the first time.
Styling had a more European look that certainly appealed to me, having been weaned on Dominators and Thunderbirds. The basis of the RD was a duplex tubular frame that could have been a downsized Featherbed. Detailing gave the impression of quality with a large four-gallon fuel tank, usefully substantial dual seat, a powerful disc brake and tidy instruments. Power was a claimed 30 bhp at 7500 rpm and weight (with fuel) of 350 pounds.
At the time there’d been much talk of ton-plus 250s including Suzuki’s T20 Super Six and Ducati’s Mach 1, but little in the way of supportive evidence. So I was keen to find out how the new Yamaha would perform.

Disengage brain before RIDING

Nothing could match Laverda's race-bred road bike for unadulterated, single-minded purpose. Roland Brown gets the chance to find out if it lives up to its image.
ONE image sums up the Laverda Montjuic perfectly. It’s an illustration, created for a bike magazine shortly after the 500cc parallel twin had been released in 1980, that shows a leather-jacketed guy sitting on a Montjuic - about to ride off but first reaching up to remove his brain through a hinged lid in the top of his crash helmet.
Tasteful? Not at all. Appropriate? Absolutely. The Montjuic was the archetypal ‘brain out’ motorbike, best ridden after you’d removed your grey matter and left it in a safe place.
That might have been a slight exaggeration, but the machine named after Barcelona’s city centre circuit (where Laverda twins had been raced successfully) was certainly one of the craziest, most outrageous bikes of its era.
Few models before or since have been so single-mindedly created for fast and furious hooliganism as the Italian factory’s improbably loud and bright orange single-seat sportster - which, like the mighty Jota and Mirage triples before it, was originally created by Laverda’s UK importer, Slater Brothers.
The Montjuic traced its roots back to the Alpino, Laverda’s first 500cc parallel twin. This was a roadster, introduced in 1977, that featured pleasant styling, slightly raised handlebars, sound chassis and 497cc, dohc engine. A year later Laverda uprated it to the Alpino S, with extra power - but even the S model produced a modest 44 bhp and had a top speed of barely 100 mph.
There was little actually wrong with the Alpino S, except for the fact that it cost roughly twice as much as Honda’s CB400 twin yet was not much faster.
The Alpino lacked the performance and charisma that might have made it a sales success at that price, but Laverda added excitement in the Italian market by promoting a one-make race series, the Coppa Laverda, using a ‘Formula’ version of the twin.
The Formula bikes - all identical to each other - were essentially Alpino S models with low handlebars, hotted-up engines, stripped-down chassis and racing bodywork. Motors were tuned to give 52 bhp, using high-compression pistons, open Dell’Orto carbs and free-breathing exhausts. The chassis lost 16kg of weight with the removal of unnecessary parts and the use of a lightweight one-piece tank and seat.
Europe wide enthusiasts
LAVERDA promoted the Coppa series enthusiastically, setting up sponsorship deals and providing a large truck of spares at the rounds held at circuits across Italy. The Formula twins themselves were reasonably priced, costing little more than the basic Alpino roadster in Italy. They were also in demand from enthusiasts in other countries including Spain, France and Holland.
There was a similar race series in Germany but it was in Britain that the next development came when importers Roger and Richard Slater realised that the Formula could be modified to make a high-performance roadster.
And so the Montjuic was born. The Formula was easily converted to make it legal for road use, sold with a box containing lights and other necessities. Even so, the Montjuic had fewer concessions to civility than just about any other machine on the road.
Adjustable ‘Jota bars’, angled steeply downwards, sat behind a small handlebar fairing. This, like the side panels and seat hump - which even had a semi-circular lower edge to fit a racing number plate - was painted in Laverda’s traditional racing orange. The rearset footrests, mounted on alloy plates, were located close to where the Alpino’s pillion pegs had been, giving a very cramped riding position. The thinly padded single seat did nothing to help the rider’s comfort but this was a bike built for speed and aggression with virtually no regard to anything else.
Its unfiltered Dell’Ortos sucked mightily and sprayed petrol stains over the side panels, while the two-into-one exhaust system was loud enough to alert police forces in the neighbouring county.
That pipe got plenty of chance to sing, too, because the Montjuic was a bike that just had to be revved hard. Although its Nippon Denso tachometer was red lined at 8000 rpm, peak power (normally estimated at 50 bhp) didn’t arrive until nine grand. And the motor was good for 9500 rpm until, on occasion, it blew up in expensive fashion. Brembo’s disc brakes gave powerful stopping and the Montjuic’s light weight, strong tubular steel frame and firm, race-ready Marzocchi suspension helped give excellent handling until about 100 mph, when the handlebar fairing triggered a slight weave.
That problem was addressed with this bike, the Montjuic Mk2, which was introduced a couple of years later in 1982. This featured a slightly larger, frame-mounted fairing and a one-piece seat/side panels unit.
By this time the British importer’s idea had been enthusiastically adopted by the Breganze factory and the majority of Montjuics exported to markets as far away as Australia and South Africa, as well as many European countries, were the more stable Mk2 model.

BARRY'S Grand Prix bike for the road

Chris Pearson delves into the internals of the Suzuki RG500 square four ‘Gamma’ and discovers just how similar it was to the real thing we featured last month.
IN 1984 a Yamaha advert boldly stated; “No one has ever built a road machine so close in technical basis to a current GP winner. Quite frankly we do not expect that anyone else ever will.”
How wrong they were. By 1986 they had good cause to regret that ad campaign. Put side by side, the Yamaha RD500, Honda NS400 and Suzuki RG500 Gamma could all have passed for the top manufacturers’ attempts at producing replicas of their respective GP racers. But two of them were mere shadows of the original racers.
Not to say that the Yamaha and Honda were rubbish - far from it - but it was the only the RG that could justify the boast made by Yamaha. It was so close to the machine raced by Sheene as to exceed your wildest dreams.
By now Yamaha had become, not surprisingly, a little muted about their 500/4, preferring to concentrate on the new FZ750 and TZR250 instead.
Eastern promise
THE Suzuki actually began life as far back as 1983 and was first seen in the Japanese market as a 400 in 1984. That heavily restricted bike gave us no indication of the potential of the full-blown half-litre version that would later be brought to the west.
Thankfully, the marketing men at Suzuki were brave enough to give us not only the visual image but also a real taste of GP performance with their nimble Gamma 500 - endowing the machine with plenty of fire from within its four pot belly.
I can remember riding both bikes for the first time upon their release and feeling that Yamaha had chickened out in the performance department compared to the Gamma. The RD is big and heavy with little in the way of stunning performance.
Likewise, the NS400 triple Honda was supposedly produced in the likeness of its successful GP machines. In fact the NS could not have been further removed from the Freddie Spencer race bike it was built to emulate. The triple engine was ‘upside down’ when compared to the racer, and no comparisons could ever be made with the engine components, performance or design.
In complete contrast the Suzuki is almost an exact replica of the race machine. The crankcases, barrels and general engine layout are virtually identical to the bikes ridden by Sheene, Mamola, Crosby and the rest of the factory boys.
It can be traced directly to the 1983 factory XR45 ridden by Randy Mamola and Franco Uncini.
I have a little theory that so far has held true throughout my time in biking. That is, any race replica producing less than 80% of the horsepower of the real McCoy is nothing more than a toy.
When this is applied to the NS, RD and the RG, this becomes clear. For the race rep to be a serious tool it must scare the pants off the unwary and bring out the very best from experienced riders.
With a top speed of 143 mph and power around the 95 bhp mark at 9500 rpm, the RG500 is one serious motorcycle - a detuned version of the race bike, not simply a replica.
The bore and stroke is identical in design to the race machine although a shock damper was added to the layshaft to reduce loads between the cranks and the clutch/gearbox.
Starting is by kickstart and, unusually for a Japanese machine, as the mechanism does not drive the clutch outer gear but the input shaft of the gearbox, it has to be started in neutral. The compression ratio is a conservative 7:1 while the engine breathes through four flat-slide Mikuni VM28SH carbs mounted like the racer in pairs either side of the engine. When viewed from the side these carburettors are incredibly short, only 36mm - the key to good power from a disc valve engine.
Just like the real racer the gearbox is a cassette type and can be removed in double quick time enabling different ratios to be fitted. The factory race bikes of ‘83/’84 could utilise up to six different ratios for the first four gears and five for fifth and sixth, and this feature was retained for the roadster.
The ratios chosen for the roadster gearbox were, apart from the ridiculously high first gear, pretty well matched for high-speed use although the five locating dogs on each pinion did slow down the selecting mechanism somewhat.
It would be reasonable to assume that although no race kit was announced or produced by Suzuki for the Gamma, it was obviously originally designed to accept go-faster goodies to create a formidable production class race bike.