| Yamaha YZR500, 1973-1980 |
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Among the Japanese motorcycle companies, it was always Honda which managed to get into the act first when it came to Grand Prix racing.
Honda was the dominant force in GP racing in the 1960s and when it unleashed its 500cc four cylinder bikes in the hands of the late Mike Hailwood and Jim Redman, they came oh so close to bringing the 500cc rider's world championship to Honda. But it wasn't to be... Honda retired from top flight world championship GP racing at the end of the 1967 season and they didn't return until the early 1980s with Mick Grant on the oval-piston four stroke NR500 which was an unmitigated disaster. However the world no. 1 bike maker finally did what was unthinkable - build a two-stroke 500cc machine on which Freddie Spencer finally won Honda's first 500cc rider's crown. To Yamaha however went the honour of not only bagging the first ever 500cc rider's world championship title - the first Japanese bike maker to achieve this, but also being the first in the history of the sport to do it on a two-stroke machine! The seeds for Yamaha's move into the premier blue riband class of bike sport were sown when engineers decided to couple two of the firm's liquid-cooled, twin-cylinder TZ250 motors to come up with a 500cc four. This engine was a simple (if at all it could be referred as such then!) piston-ported design with a single petal reed valve. The first 500 engine was run in July 1972, and the machine, model number OW20, was tested in December by old Yamaha hand Motohashi. Designed by chief designers Naito and Matsui, the two-stroke four produced 80bhp at 10,000rpm and could reach 165mph.
This wasn't Yamaha's first four-cylinder two-stroke though. In 1968 it had raced a 250cc vee-four which was an incredible piece of engineering, dishing out 73bhp at a shade over 14,000rpm, sported an 8-speed gearbox, twin ignition systems and an autolube system. A 500 was on the cards but at the end of the 1968 season the FIM played spoilsport and banned four-cylinder machines from the 250cc class in order to keep the costs of racing low. Yamaha pulled out of World Championship Grand Prix racing as a works team but crucially continued to supply bikes like the TD1s and TD2s plus their liquid-cooled successors the TZ250s to privateers. However the competition department had kept its hand in and thus was born the Yamaha 500cc challenger. In early tests, the reed valve inhibited maximum flow into the crankcases and for a while the reed valves were junked for tuned inlet tract length intakes. By designing the engine with the correct distance from the crankcase to the bell mouth of the carb, the shock wave that travels backwards and forwards along the tract could be employed as a valve that would ensure little gas could escape from the engine. However, the reed valved engine was used in the TZ500's first race and the men entrusted with the job of spearheading Yamaha's foray into the premier class were Finn Jarno Saarinen and Japanese rider Hideo Kanaya. Please note that all following pictures are in one size only !!! These were the first two pictures "leaked" to the Press in anticipation:
But shortly thereafter the official studio shot was sent out that showed the Yamaha 0W20 in all its glory.
The first race was the French GP in April 1973 and Saarinen was brilliant on the machine which featured twin rear shocks, twin discs up front and a single disc at the rear. He just ran away from the pack beating Phil Read on the MV Agusta quite comfortably. To make it a notable debut for the maker and its machine, Kanaya came home third.
In the next GP, the Austrian, in atrociously wet weather, Jarno and Hideo Kanaya were again first and second. In the German GP Jarno was leading comfortably when he had to retire because of a snapped chain! The terrible crash during the 250 cc race in Monza a week later, in which Jarno Saarinen and Renzo Pasolini were killed, made Yamaha decide to withdraw from the 500 cc class for the remainder of the season.
Yamaha looked for another rider and found multiple World Champion Giacomo Agostini eager enough to accept the challenge. Ago had 2 GP wins to start with in 1974. Today the Yamaha 0W20 stands in Yamaha's "Communication Plaza" in Japan as an important piece of history. This is the updated version of the 0W20, internally called the Yamaha 0W20A, for the 1974 season. This is the machine as being used by Giacomo Agostini and Teuvo lansuvuori. Together they won the Manufacturers World Championship in 1974
The Yamaha 0W23 was the machine that brought Giacomo Agostini his first Yamaha 500 cc World Championship in 1975. The 0W23 was lighter and had a smaller wheelbase, the engine had a cassette-type gearbox and the rear swing arm was constructed from square profile material. Also the exhausts were completely different. Officially Yamaha did not enter for 1976 but the 0W23 was used by Johnny Cecotto under the internal code 0W26.
The new Yamaha 0W35 for 1977 had a smaller engine with 56 x 50,6 mm bore/stroke instead of the old 54 x 54 mm square dimensions. For the first time powerjet carburettors were used and the reed-valves were not used anymore. Steve Baker became 2nd in the Championship and also Johnny Cecotto was official rider in the team.
The Yamaha 0W35K for 1977-78 was the machine with which Kenny Roberts clinched his first of three successive World Championships after having won 4 GP's with it in 1978. This was the bike that used for the first time the "Powervalve" system, which was already tried on the Motocross machines. According to Shiohara-San, one of the engineers, the Powervalve contributed more to the increased performance than anything else before. Johnny Cecotto also won 2 GP's with this machine.
For Kenny Roberts' second assault on the World Championship the Yamaha 0W45 was built with an improved engine. The engine now had VM-type carburettors for increased power and torque. Next to Kenny Roberts also Christian Sarron and Johnny Cecotto were riding this machine. The 0W45 was also the basis for the TZ500 productionracer in 1980 (4A0 model).
The 1980 Yamaha 0W48 was the first machine with an aluminium frame in order to reduce weight further. The YPVS system was improved again and many other parts were made smaller. The front brake calipers were made of aluminium as well. Kenny Roberts won the first 3 GP's and scored his 3rd World Championship.
Later during the 1980 season Yamaha brought the modified Yamaha 0W48R into action. "R" eversed = (the two outer cylinders were reversed). The improved exhaust layout resulted in 7 ps +. The first 0W48R had the 0W45 frame but later a completely new aluminium one was built. So Kenny rode 3 different bikes during that hectic 1980 year !
(Author: Adil Jal Darukhanawala, Source: Overdrive, March 2001)
The 1975 version of the TZ500 with the monoshock rear suspension. Note the Finnish flagon the fairing. It signified the bike as that used by Giacomo Agostini's Finnish team-mate - Teuvo Lansivouri.
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