Where legends live on..

Yamaha YZR500 OW60 - One Year Wonder Copycat Stroker

The Japanese company reaped a quartet of World Championships with its piston-port two-strokes, just as it’s done so far in MotoGP with the YZR-M1, even though by 1980 all other two-strokes in each Grand Prix class, from 50cc tiddlers up to 500cc fours, employed rotary-valve engines of the kind invented a quarter-century earlier by MZ’s Walter Kaaden.

This technology was then purloined by Suzuki in 1961, by enabling his rider-engineer colleague Ernst Degner to defect to the West, after which only Yamaha swam against the disc-valve tide in preferring to employ traditional piston-port two-stroke technology on its race bikes.

Yamaha had been wedded to piston-port engine designs for its customer racers ever since the introduction of its first such bike, the 250cc parallel-twin TD1 in 1962. But its RD56 factory GP bike which debuted in 1963, and took Phil Read to the 250cc World title the following year, used a disc-valve motor profiting from MZ technology that was by now more widely shared – Suzuki and Yamaha are both based in Hamamatsu, so it’s not hard to imagine how that came about!

Read’s later title-winning 125cc RA31 and 250cc RD05 V4s were rotary-valvers too, but when Yamaha finally entered the 500cc category in 1973, the OW19 inline four which Jarno Saarinen took to victory in its very first race in the French GP at Paul Ricard, was a piston-port design.

His tragic death a month later at Monza led to Yamaha’s withdrawal for the rest of the season, so it wasn’t until 1975 that Giacomo Agostini gained GP racing’s ultimate prize for Yamaha, which with the piston-port OW26 became the first Japanese company to win the 500cc World title. And while its Suzuki neighbours then gained the upper hand, courtesy of Barry Sheene who won the championship in 1976/77 with the rotary-valve square-four RG500, Yamaha struck back in 1978, when Kenny Roberts won the first of his trio of World Championships with the piston-port OW35, repeating the feat the following year on the OW45, and again in 1980 with the reverse-cylinder OW48R.

By then Yamaha had already conceded dominance of the 250cc and 350cc classes to the rotary-valve Kawasaki tandem-twins, and Roberts’ 1980 500cc World title had been a close run thing, with the increased performance of the disc-valve Suzukis providing a lesson that Yamaha decided they needed to learn, in order to build on their serial success.

The rotary-valve format provides greater potential for outright power via asymmetrical inlet timing, and Yamaha evidently decided they must adopt this, to redress the performance gap that had opened up the previous season between their piston-port OW48R, and the Suzukis.

For 1981 they bit the bullet, and effectively produced a copy of the RG500 as the first of their short run of rotary-valve 500s, the square-four OW54, leaving the uprated OW53 version of the piston-port OW48R inline fours to provide support for Roberts from the likes of Marc Fontan and Barry Sheene in defending his title.

After a disastrous DNF debut in Austria, Roberts won the next two races in a row in Hockenheim and Monza with the square-four, after his engineer Kel Carruthers had radically altered the cylinder porting. Yamaha had positioned the transfer ports 0.5mm too high, so Carruthers redressed this by machining down the base of the cylinders.

Although KR still didn’t care for the more sudden power delivery compared to what he was used to; this was the first time he’d ever raced a disc-valve machine, of any capacity, it was evident that Yamaha’s bet had paid off.

But a series of handling problems, partly due to the Goodyear tyres Kenny alone used, as well as component breakages, set back his season, and he wound up third in the points table behind new champion Marco Lucchinelli, and Randy Mamola, both on Suzukis. Barry Sheene did win the final race of the season in Sweden on a rotary-valve OW54, having been supplied with one from the fourth round onwards.

Words: Alan Cathcart Photographs: Stefano Gadda