Yamaha XS1, XS2 andTX
Japan'soverheadcam take on Britain'sbest to be the world'stop dog.
Yamaha's first big four-strokes were great, good-looking machines
FOR A COMPANY THAT MADE ITS REPUTATION with two-strokes, Yamaha has always had something of a thing for large capacity fourstroke twins. Think the Ducati aping TRX850, its 850/900 TDM cousin, or how about the massive trail iron, the Super Tenen§ XT1200? Recently the firm has enjoyed amazing success with the DOHC 700cc MT-07,yet this is a love affair which goes back to the late 1960s.
XSl GENESIS
Yamaha's seminal 650 twins were created in response to a 1965 USAmove towards cleaner air.The nascent bill was due to be enacted in 1968 and so,just as Yamaha's smoking twins were becoming popular stateside, it looked like they might well be doomed. Therefore Project 049, headed by Daisuke Tanaka, commenced in August 1967 to develop a marketcompetitive four-stroke twin. The bike's origins were absolutely atypical and didn't follow what many might view as a conventional or industry standard route to designing an engine from scratch. Yamaha had worked with Toyota throughout the 1960s and by 1964 had cooperated successfully enough to co-develop a six cylinder engine destined for the Toyota Crown. A year later the same team/project had a DOHCversion ready for the super-sleek 2000GTsports car that would later appear in the James Bond film, You Only Live'Twice.
Initially and not a little bizarrely, Yamaha initially considered dabbling with a 650cc two-stroke twin, but soon realised it was a flawed concept. With
Toyota's blessing the 650cc four-stroke twin copied two cylinders from the car with a 1mm reduction in bore size, but ran with just a single overhead cam for simplicity. Rather than follow the rest of the 2000GT's architecture, Yamaha rather cleverly went with what they knew best - a ball and roller bottom end that was, in essence, a larger version of their hugely successful YR1 350 stroker twin.
This also allowed for a low pressure, high volume oil pump which, allied to substantial joining faces on the horizontally split crankcases, effectively precluded any oil leaks. Initial cam designs did little for power output with the engine making no more power than a period 350 stroker twin. However, by using the computer ofYamaha Musical Instruments at night, the team had the all-new motor delivering reliable 53bhp at 7000 rpm.
Both the bike's transmission and chassis borrowed from the then state-of-the-artYRl 350,which had only just been launched that year, but for inlet technology Yamaha went offshore. Working in partnership with Japanese carburettor maker Mikuni, Yamaha developed a CVcarb system that was made under licence to Solex. The reasons for going down this relatively unorthodox route were smoother running, improved fuel consumption and reduced emissions. The bike broke cover at the 1969Tokyo bike show with export models readied for delivery in America early the following year. •
THE BIKES
The initial 1970XS1in candy mid green with white decals is the purest of the breed and, predictably, the most expensive now. Half a century on after its launch, an original version still has all the qualities that made it such a surprising success within the pivotal USA market. Despite the soft rear shocks and handling that would never threaten Norton Featherbed models, it really isn't the jelly-on-a-plate quality the bike's detractors would have you believe. Its key virtues are its innate ability not to leak oil, an electrical system which was streets ahead of the various Luca,Wipac et al and, for a big bore parallel twin, a surprisingly acceptable level of vibration. Yamaha knew that vibes were the design's Achilles heel and therefore, rather sensibly, introduced rubber mountings at all and any key areas that might suffer from being stressed. Period road tests of the launch model from America were unswervingly positive. The bike's finish was regularly commended, everyone loved the punchy motor, more than a few journalists actually praised its handling, and no one found its near 110mph top end was slow. It looked like Yamaha's first four-stroke was a success.
1971 saw Yamaha taking on board the various comments and feedback from their dealers as they prepared for the bike's European launch. Changes to footrests, rear brake pedal and kick-start levers all reflected vital customer survey findings. A subtle tweak of the pistons reduced compression ratios slightly and twin-walled exhaust tubing was drafted in to reduce noise levels. The bike was available in most of Europe, but not in Britain; some argue Yamaha's importers simply didn't think they could sell the XSl-B against the offerings of BSA,Norton and Triumph. The original XSl was never sold with indicators as standard (they were offered as an option), but in America at least the XSl-B was suitably equipped with the front units mounted off the top nut of the forks. In Europe and Australia the bike seems to have been sold (if not marketed) as an XSl-F model with a rectangular rear light and indicators mounted on the headlamp ears. Regardless of market, both the B and F models were now painted in candy orange which, in reality, looks suspiciously like Fizzy gold.•
"Its key virtues are its innate ability not to leak oil, an electrical system which was streets ahead of the various Luca, Wipac, et al and, for a big bore parallel twin, a surprisingly acceptable level of vibration"
1972 saw the biggest change - the big twin now came with a self-starter as standard. Yamaha had been caught napping by Honda's CB750/4and more importantly its fitment of an electric foot. Half a litre of oil capacity was sacrificed to install the starter motor outside of and underneath the engine. A cartype Bendix engaged with a series of gears to turn the motor over aided by a decompressor on the RHS exhaust valve. Rather cleverly,Yamaha fitted a pulllever beneath the twist grip that pushed the valve off its seat whilst activating the starter motor. In a flash Yamaha had aced the big brit twins in terms of bragging rights and swiftly won itself more customers. The XS-2 also now came with a rather competent disc front brake grasped by a twin-piston caliper, made under license. Paint schemes changed to embrace Yamaha's global roll out of the all-new Europa look. America and Canada received the XS-2 in candy red and white with Japan/Australia/Europe variously getting the black and candy orange with yellow pin striping or the black and candy dark red with yellow pin striping. Mitsui Machinery, the then UKimporter, was reluctant to commit and remained concerned that a still relatively buoyant Triumph factory's products would still eclipse the big Yam. On this occasion they were correct; an overtly negative road test did little to enhance sales of the UK's sub-80 units with some still unsold three years later.
1973 saw the XS-2 rebranded as the TX650. Yamaha had embarked on a campaign of parallel twins including 350, 500 and 750, all based around a vibration reducing balancer system. The 650 really had no commonality with the other machines, but a commercial decision was taken that the name would change regardless. The bike, sometimes referred to as an XS-2B,varied little from the previous model other than a fresh paint job in pale candy blue with gold and black graphics. •
Scour the web and you will find numerous references to the fact that Yamaha's 650 twins are, in fact, little more than upgraded copies of the Japanese Hosk and/or Showa 500cc parallel four-stroke twins. There are also references to both of these engines being strongly influenced by West German manufacturer Horex and an implied link that the 650cc XS series engine is somehow related to this European manufacturer. The various associations are, to be brutally honest, feeble to say the least, but the venerable Yamaha twin does deserve to have its name cleared.
At the beginning of the 1950s Horex embarked upon a 500cc OHCtwin engine design aimed purely at racing with the motor built around a four bearing crank for reliability. By 1952 the bike had gained a second camshaft and the name lmperator. A couple of years later road-going versions with a single cam went on general sale in 400 and 450cc guises. At the same time Hosk was looking to move on from copies of European singles so naturally looked to the West as it had all the other Japanese firms for inspiration
- thus the Hosk 500 was born. Fellow motorcycle producer (and later suspension specialists) Showa latterly bought out Hosk and, naturally, offered the 500 under their own name...so far, so good. Where the story gets cloudy is in 1960 when a burgeoning Yamaha starts acquiring knowledge and expertise via tactical acquisitions, including Showa. This rather obvious, if questionable series of convenient links has led many to assume that the XSl and it spawn are little more than re-engineered and enlarged Showas/Hosks/ Horexs. Although some will likely remain fixated by this apparent conspiracy theory, the fact remains that Yamaha themselves have always stated the XSl was a fresh design and not a re-hash. Quite possibly they may have looked inside a Showa 500, but only to glean insight. If the big bore twin was ever 'inspired' by anything European it was the big British twins that they looked at - only with a typically Japanese take on the engineering. If you need further proof, compare the Yamaha's bore and stroke alongside a BSAA65!