1981

"King" Kenny Roberts & "Sir" Barry Sheene duo

#7 B. Sheene won the Sweden GP

Under contract with Yamaha, Kenny Roberts was out to win his fourth consecutive title in 1981. Barry Sheene, who has a British knighthood, also joined the Yamaha team. This put the top British and American riders both in the YZR500 saddle. In addition, four riders were contracted by overseas Yamaha distributors to ride on the TZ500 production model. There were some good battles with Suzuki riders as Roberts managed to finish 3rd in the ranking by winning two races. Sheene finished fourth with a single win. However, the pair were unable to maintain Yamaha's streak of consecutive rider titles. The title this season went to Suzuki's Marco Lucchinelli, who came on strong from mid-season.

Roberts raced on the new YZR500 (0W54) this season. The engine layout was not the usual in-line-4, but a "square-4," with the four cylinders in a square configuration. This was the first time Yamaha employed this layout for GP racing. From the opening round, however, the Suzuki machines were dominant. In the first race in Salzburg, Suzuki riders Randy Mamola, Graeme Crosby, and Hiroyuki Kawasaki swept the podium, while Roberts was unable to finish the race. Fighting back, Roberts won the following races at Hockenheim and Monza, and it appeared as if he would stay in good form through mid season. However, with brake failure and other unfortunate events he was unable to perform to his full potential this season.

Sheene, on the other hand, started the season using the YZR500 (0W53) powered by an in-line-4 engine and finished 4th in the opening round. He also managed to finish 6th and 3rd in the two following races. From the fourth round in France he switched to the YZR500 (0W54) with the square-4 engine. Although he was able to take 4th in France and Italy, as well as a 2nd-place finish in Imola, he struggled through the final stages of the season with some no-point finishes. He rallied to show his true potential in the rain-hit final round in Sweden, however. Starting from pole position, he recorded the fastest lap of the race and took his first win of the season by finishing just in front of Boet van Dulmen (Yamaha). Yamaha's YZR500 development rider Ikujiro Takai also raced in the British GP and managed 8th place.