The Yamaha YZR500 machines from the period 1991-2002 are somewhat more fresh in your memories maybe, but they are fantastic to look at !
From 1991 onwards minimum weight for 500 cc GP racers was 130 kg so Yamaha concentrated for the 0WD3 on a new suspension system. This was designed together with Ohlins and called “CES”. It was an electric system with sensors measuring the suspension stroke, which was “translated” and fed-back to the suspension. The rider could adjust the system as well from the handlebars. Wayne Rainey won 6 GP’s with the 155 hp 0WD3 and his second World Championship. John Kocinski also won a GP, therefore Yamaha had another Manufacturers title as well. And Peter Goddard won the Japanese Championship, so it was a good year for Yamaha!
Yamaha’s engineers found a few more ps for the 1993 Yamaha 0WF2, it now had 165 hp. It needed a new frame for the larger lateral forces. But Wayne Rainey used the 0WF2 only for the first 9 races, thereafter he swapped the frame for a ROC one. ROC also built “customer” bikes as you all know.
Luca Cadalora was successful with the 1994 Yamaha 0WF9. It brought him the 2nd place in the World Championship that year. The frame was again new and the engine had even more power. Norick Abe also had his first GP ride on this bike. The 1995 version had a “Ram-air” system forcing cold air to the carburettors.
In the 1996 Yamaha 0WJ1 the bore/stroke was changed again back to the previously used 54 x 54 mm. It gave under the new conditions a better spread of power through the rev-range. Yamaha also used a new material for the pistons and the frame design was modernized in not using a sub-frame for the seat anymore. Norick Abe scored his first GP win on the 0WJ1 and also Loris Capirossi won a GP.
The Yamaha 0WH0 for 1997 had a new engine with an enlarged engineangle of 75 degrees. This was also done to create more space for the large air-box needed. The shape of the exhaust ports was changed into a kind of “T” shape. The motor had new crankshafts and the drive axle of the gearbox was mounted higher in the crankcases. Luca Cadalora won 2 GP’s with it and finished 6th in the World Championship, Norick Abe became 7th.
In 1998 the bikes were run for the first time on unleaded fuel. The Yamaha 0WK1 had therefore a different compression ratio, a new exhaust system and the Mikuni carburettors were exchanged for Keihin ones. The bike had good power as Yamaha had also reduced the internal friction and improved the cooling system of the bike. Remarkable was that the cylinder angle was decreased again back to 65 degrees! Norick Abe, Jean-Michel Bayle, Regis Laconi and Simon Crafar were the riders in 1998. Max Biaggi and Carlos Checa came into the team for 1999. Both Biaggi, Abe and Laconi won a single GP in 1999.
The 2000 Yamaha 0WK6 was a further development of the 0WK1. It had new cylinders, cylinder heads and (of course) a new exhaust system. The geometry of the frame was changed together with the dimensions from the engine. The engine management was also new, altogether quite much for just a “further update". With the new cowling the machine was also quicker. Garry McCoy won 3 GP’s with the 0WK1, Max Biaggi won 2 GP’s and Norick Abe 1, enough for another Manufacturers title for Yamaha. The last one was 7 years ago!
As the two-stroke period became to an end, the last 2 models were not entirely new. The 2001 Yamaha 0WL6 was similar to the 0WK6, but many details were improved. Riders could choose from different rear arms (with different length). Max Biaggi had 3 GP wins and scored the second place in the World Championship.