The next 10 years for the Yamaha YZR500 (1981-1990) were quite spectacular.
All pictures are in one (larger) size only, but maybe you can enlarge them yourself !!
The Yamaha 0W53 of 1981 is the last GP racer with a four-in-line motor. The frame was an updated version of the Yamaha 0W48R. The picture shows Barry Sheene's machine. Actually it was a "just-in-between" model awaiting the new Yamaha 0W54.
Kenny Roberts received the Yamaha 0W54 for the 1981 season, a square four with rotary valves. The bike had a broader powerband but was more difficult to ride as it was heavier. Barry Sheene got this bike also later in the season and won the Swedish GP with it.
The 1982 Yamaha 0W60 was the second generation of the square four and was 6 kg lighter. Rear suspension was improved. In the first GP Roberts and Sheene were 1 and 2 but that was all. Graeme Crosby became second in the Championship with the 0W60. Kenny Roberts moved to the Yamaha 0W61
Without the cowling the details of this machine are clearly visible.
Again Yamaha used their experience and after the rotary valves on the Yamaha 0W54 now the V-four layout of the famous 250 cc RD05A was used for the new Yamaha 0W61 in 1982. The same reasoning as in the 1960's led to this change. Yamaha wanted to make a smaller bike with better handling. The carburetors and rotary valves were mounted between the cylinderbanks (60 degrees "V"), a method still used today. The rearsuspension unit was mounted square on the driving direction and the suspension travel. The frame was a pre-Deltabox type. Kenny Roberts used the bike for the first time on the Salzburgring and set a personal record with it.
The second V-four Yamaha 0W70 1983 bike also had the first aluminium "Deltabox " frame and a 17 inch front wheel. Rear suspension was of the "bottom-link" type, still used today. With this bike Kenny Roberts fought with Freddy Spencer many fantastic races and in the end Freddy just clinched the World Championship ahead of Kenny. Eddie Lawson became 4th on a similar machine.
The beautiful aluminium frame is evident on this picture
In 1984 Eddie Lawson won the World Championship with the new Yamaha 0W76. Yamaha turned back to reed-valves as with the new materials that became available more power and better starting was assured.. Eddie won 4 GP's with the bike.
Again a new engine was made for the Yamaha 0W81 1985-86 machine. Crankshafts were now counter-rotating in order to achieve less gyroscopic effect. Eddie Lawson became second in the Championship and Christian Sarron third. In 1986 the bike got slightly more power resulting in a maximum of 145 ps. In 1986 Eddie lawson again won the World Championship and Taira became Japanese Champion with this bike for the 3rd time.
The 1987 Yamaha 0W86 had a new exhaustsystem, the engine was re-located and the cooler had a different size and shape. Power was now 148 ps. Randy Mamola won 3 GP's and Eddy Lawson 6 GP's, so Yamaha had again the Manufacturers Title.
For 1988 Yamaha rebuilt the 0W98 with a different V-angle (60>70 degrees) in order to create more space for the larger reed-valve system. The rear swing arm was a-symmetrical because of the new exhaustsystem. Eddy Lawson won 7 races and his third World Championship and with also Kevin Magee and Wayne Rainey as GP winners Yamaha clinched the Manufacturers title once more. During one race Eddy won with carbon discs for the first time.
The Yamaha 0WA8 for 1989 was an update of the 0W98 and used data-recording for the first time. Eddie Lawson became second in the World Championship, Christain Sarron was third. Fujiwara won the Japanese Championship for the 3rd time with this bike.
The 1990 Yamaha 0WC1 had an upside-down front fork and power was increased to 155 ps. Wayne Rainey won 7 races with it and scored his first World Championship. Yamaha again won the Manufacturers World Championship, now for the 6th time. The 0WC1 motor was also later the basis engine which Yamaha made available for customers, as in the ROC bikes.