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 OW45 (1979) - The
representative piston valve parallel four
As the second generation YPVS-equipped model, the OW45 employed a processing technique called honing relief to shave the area around the exhaust port to
micron accuracy in order to further increase reliability of the YPVS function. The VM carburettor adopted on this model that eliminated the air side cut-away also contributed to outstanding acceleration
performance. In the '79 series this machine was ridden by Roberts, Cecotto and Christian Sarron. After missing the series opener due to injuries, Roberts returned to win round two at Salzburgring, then
place second at round two in West Germany, win round four at Imola and round five in Spain. This put him on top in the ranking and on his way to his second consecutive season title with five season
wins.
This OW45 would be representative of six generations of YZR500 machines powered by a liquid-cooled, parallel-four, piston-valve engines that continued from the OW35 and OW35K through the
OW45, OW48, OW48R and OW53. It also served as the base model for the TZ500 production road racer released in 1980.
 OW48 (1980) - The first aluminium frame model
The OW48 spec was the first
YZR500 to adopt an aluminium frame. This frame, using squared aluminium stock, greatly reduced the weight of the chassis. Weight reducing technologies were also employed in other parts of the machine as
well. Improvements to the YPVS system boosted power across the full rpm range, and improvements to the cooling system ensured greater reliability. Compact designs for many of the machine components
further reduced overall size. The front and rear suspensions were also re-designed, and the front brake was given an aluminium caliper. Roberts started the '80 GP500 season with three consecutive wins at
the opener at Misano, round two at Jarama and round three at Paul Ricard. Roberts won his third consecutive championship title this year running five of the eight rounds on this OW48 and the remaining
three on the OW48R spec which featured rear exhaust on the two outer cylinders.
OW48R (1980) - Parallel four for Roberts' third title
The OW48R spec introduced at the Dutch GP, round
four of the '80 series, was not based on the OW48 with its aluminium frame. It adopted a steel frame of the type used on the previous year's OW45 spec and mounted an engine with rear-directional
(reverse) exhaust for increased power output. Introducing rear exhaust on the first and fourth cylinders, in other words the two outer cylinders, increased power by 7PS. The R in this spec's name stood
for reverse.
Roberts began the '80 GP500 season with three consecutive wins on the OW48 and then rode the OW48R in round four, the Dutch GP. In this race he was forced to retire due to an air
leak in one of his tires, but he rode this spec again at round five, the Belgian GP, and finished third. For rounds six and seven he returned to the OW48 and mounted the podium with two second-place
finishes. For the final round he rode a OW48R with aluminium frame (prototype for the next year's OW53) and finished fourth. While changing machines three times in the course of the season Roberts won
his third consecutive title.
 OW53 (1981) - The last parallel four model
The OW53 spec that appeared in 1981 was the successor to the OW48R with its rear-directional exhaust configuration for
the two outer cylinders. It would also become the last YZR500 to mount a parallel-four engine. The frame was a further maturation of the squared cross-section aluminium frame first introduced on the OW48
and mounted on it was the same type of rear exhaust engine as the OW48R. The basic dimensions were kept the same as the OW48. This year, 1981 would see the debut of the first square-four engine YZR500
(OW54), ridden by Roberts. Meanwhile, this OW53 would be ridden by Barry Sheene is the first three rounds of the '81 series, where he finished fourth at Salzburgring, sixth at Hockenheim and third at
Monza.
 OW54 (1981)- Square-four with rotary disc valve
The 1981 model YZR500 (OW54) was the first Yamaha racer to mount a square-four format engine on an aluminium frame. For the intake system
the conventional piston valve was replaced by a rotary disc valve with its outstanding power development characteristics in the high-speed range. On this machine Roberts won the first two rounds of the
'81 season, the West German GP and Monza GP. With brake trouble and other unlucky incidents in later rounds, Roberts eventually finished the season ranked third. From the fourth round at Paul Ricard,
Barry Sheene also rode the OW54 won the final round at Anderstorp.
 OW60 (1982)- The second-generation square-four
The OW60 spec debuted at the first round of the '82 season and was the
second-generation YZR500 to mount the Yamaha square-four engine. It was six kg lighter then the OW54, which has suffered from its weight disadvantage. It was also a model that saw a new suspension
challenge with the introduction of a bell crank to move the rear shock absorber. On this model, Roberts and Sheene finished one-two at the season opener, the Argentina GP. But this would be the only GP
win for the OW60, as Roberts switched to a new machine (the V4 engine OW61) from the second round of the series. It was Graeme Crosby who would ride the OW60 throughout the season, and although he never
won a round, he continued to finish high in the points and ended the season ranked second, the highest of any Yamaha rider. This machine also mounted an adjustable steering pipe as a test feature.
 OW61 (1982) - First V4 engine on a 500cc GP machine
The OW61 was not only the first YZR500 to mount a V4 engine, it was also the first ever by any manufacturer for a two-stroke GP500 machine. The
other definitive features of this model were its innovative lateral rear suspension with the shock positioned at a 90-degree angle to the direction of forward motion and a unique frame that eliminated
the under-loop, which would become the forerunner of Yamaha's famous Deltabox frame. This was the model that pioneered the two-stroke V4 engine that would eventually become the standard in GP500 racing.
After winning the season opener of the '82 GP on the square-four OW60, Roberts switched to a new V4 engine OW61 for round two at Salzburgring. In this, the OW61's debut race, Roberts finished third.
Riding the OW61 at round four in Jarama, Roberts beat his personal best lap time by a full second on his way to the win.
 OW70 (1983)- Arrival of the Deltabox frame
The 1983 model YZR500 (OW70)
was the second-generation V4 powered machine and the first to adopt Yamaha's new aluminium Deltabox frame and 17-inch front wheel. Further maturation of the previous year's OW61 and an increase in
inertial mass for the flywheel helped handling stability, while overall competitiveness was also improved with the adoption of a new rear suspension (mid-season change from bell crank type to
bottom-link type) and revision of frame rigidity. This year Kenny Roberts on the OW70 and Freddie Spencer on the three-cylinder Honda NS500 staged a head-to-head battle that continued to the final
round, were Spencer won the title by a hair's breadth. It had been one of the greatest showdowns in GP history with each rider winning six rounds and three second places and each winning six pole
positions. Roberts finished this '83 season a close second while Eddie Lawson also riding the OW70, finished fourth.
 OW76 of 1984
OW76 (1984) - Lawson's first title
The OW76 spec
that appeared in 1984 was characterized by the change from the rotary disc valve intake system used up until the OW70 to a crankcase reed valve system. By making effective use of the crankcase reed
valve intake that was coming into use at the time with a plastic resin reed, this model achieved smoother power development and better starting character. The system adopted a structure in which the
rotary disc valve drive axis positioned on the upper portion of the crankcase was replaced by a reed chamber. At the time, Yamaha was already using a crankcase reed valve system on its Mate utility
motorcycle series, but its adoption on the YZR500 brought a whole new image to this technology. In his second year of GP competition, Eddie Lawson had become Yamaha's ace rider, winning the season
opener, the South Africa GP, and going on to claim his first title with four wins during this year's series.
 OW81 (1985-86) - Opposed revolution twin cranks
The OW81 spec used in 1985 and '86
adopted a V4 engine completely redesigned with the aim of making the engine a member contributing to handling stability. On the conventional V-4 engine, both crankshafts were made to revolve in the
direction of forward motion. With the OW81, however, the two shafts were spun in opposite directions (rear shaft in the in the direction of forward motion and front shaft in the opposite direction) with
the drive force being drawn from the rear shaft. This minimized the gyro moment effect on handling stability, thus contributing to outstanding handling stability. In '85 Lawson rode this machine to
second place in the season ranking and Christian Sarron finished third on it as well. The further evolved '86 version featured boosted power output (140PS to 145PS) optimized dimensions and a new seat
shape. On this machine Lawson won back the GP title, his second. Meanwhile, in the All Japan Championships, Tadahiko Taira won his third consecutive 500cc title on this machine, which would remain the
base model as the YZR500 continued to evolve into the '90s.
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