Yamaha YZR500 OW48R motorcycle test

Menus

• Kenny Roberts’ 3rd title bike in 1980
• 4 cylinders in line, 2-stroke, 498 cm3, 102 hp, 135 kg
• Discovery
• In the saddle
• Test
• Conclusion

Kenny Roberts’ 3rd title bike in 1980

4 cylinders in line, 2-stroke, 498 cm3, 102 hp, 135 kg

This is the year of the pyramids in motorcycles, with a good number of 40-year-old birthdays, we find the golden age of the 1980s. 1980, a pivotal year. It was that year that Kenny Roberts triumphed over the theoretically more powerful rotary valve Suzuki to win the third 500 GP World Championship of his career on the handlebars of the Yamaha YZR500 OW48R factory.

Coincidentally, two decades later, his son Kenny Roberts Junior became King Kenny in turn, following in his father’s footsteps by beating the much more powerful Yamaha and Honda to win the 2000 title on his Suzuki RGV500. In doing so, he achieves a unique first in the history of the competition since it is the first time that a father and his son have won the 500 GP motorcycle title, exactly 20 years apart..

And in all of this, the Yamaha YZR500 OW48 is quite simply a centerpiece in the history of the 500GP 2-stroke. !

Test of the Yamaha YZR500 OW48R

Discovery

The opportunity to test the real Yamaha OW48R reverse cylinder with which Roberts Senior claimed the last of his three world titles came at the Assen circuit, a track on which this special machine made its debut in June. 1980.

And for that, everything relies again on men, or more exactly two men, the British collector Chris Wilson and the former factory mechanic Nigel Everett. Thanks to the enthusiasm and commitment of the collector and the restoration skills of the old mechanic, Roberts’ yellow and black Yamaha was saved from ruin and was able to return to the circuits for one of his lucky ones. friends can fly it. It’s really good to have friends like Chris…

This is the machine with which Kenny Roberts went to seek his third world title.

The collection of authentic restored 500 GP prototypes actually includes a pair of Yamaha OW48Rs. For next to Roberts’ machine from 1980 is the Akai-sponsored semi-factory version of 1981 which was piloted by Barry Sheene earlier this year before the OW54 rotary valve arrived in season..

It was in Holland, on the grounds of Yamaha’s European headquarters, that Wilson found Roberts’ motorcycle in disguised form bearing a chassis number stamping it as a 1980 machine. Since King Kenny is the only Yamaha rider to having used an OW48R with an alloy frame that year, its name stands out on this bike, even without taking into account all the specifics that make the hallmark of the American rider.

King Kenny’s OW48R sits on an alloy frame

This includes Morris magnesium alloy wheels (Sheene used Dymag, the others Campagnolo), oversized 320mm front brakes (280mm on the others) fitted with KR specific cooling ducts, a front caliper on the brake rear completed by a torsion arm on the swingarm since KR braked very hard like its past in track racing, a 40 mm Kayaba fork with a magnesium anti-dive system, a De Carbon mono-shock with separate cartridge that only factory machines used.

The YZR 500 is distinguished by its central mono-shock absorber located under the saddle

Although it was ridden for its debut in its restored form during the Coupes Moto Legende in Montlhery in May 2000 by the other Yamaha riders of that time Marc Fontan and Christian Sarron, this bike dates back a year before the latter did. piloted one for the first time. It is undoubtedly the same machine that appears in Kenny Roberts’ own collection, a fact that the American champion confirmed when he himself rode Wilson’s Yamaha at the Linas-Montlhery autodrome two years more late.

Kenny Roberts finds his old mount in Montlhery

Very close to the TZ500, the only weak point of the engine according to Nigel Everett seems to have been the extractable gearbox. A fact confirmed by the former TT winner Charlie williams who also rode Roberts’ bike in Assen which reminded him of when he rode the OW48R on the Isle of Man and had a hearty lead in the Senior TT until the gearbox breaks on the last report in Ballacrie’s fast curve, just past Ballaugh. Ouch! I can’t imagine a worse place to block the rear wheel on the Mountain Course.

Despite its 102 horsepower, the 4-cylinder in-line was significantly less powerful than that of the competitors.

Fortunately, it broke a tree, otherwise I wouldn’t be here to tell this story. When I stopped, I remembered that when I was going to pick up the motorcycle in Amsterdam, I had seen a box full of gearboxes abandoned in front of the Yamaha workshop. It should have piqued my ear, but I was so excited to get my hands on what was then a replica of the 500 GP world champion and arguably the best bike I’ve ever ridden in the world. TT, that I didn’t ask about what I saw. Maybe I should have !

In the saddle

Thanks to the attention of his team of race mechanics, led by Kel Carruthers with Nobby Clark and Trevor Tilbury by his side, Robert never encountered any racing problems in 1980. On the restored model from Assen, the transmission kept stalling until Everett found a solution? In the end, all you had to worry about was the under-damped fork that made the wheel slam in some fast corners in Assen..

Morris rims, Kayaba fork, 320mm front discs…

While 18-inch slicks are now impossible to find, Wilson outfitted their bikes with Avon racing tires, which probably have at least as much grip as the Goodyears Roberts raced with 20 years ago and which have me certainly allowed to appreciate the key advantage of the Yamaha over its more powerful rivals: its more pronounced and more forgiving handling. The OW48R is almost modern for a 40-year-old sports car, low and compact in design with a balanced setup and a narrow riding position, especially compared to the taller and longer Suzuki which was its main opponent that year..

The only difference with 1980 is the adoption of Avons tires, 18-inch slicks having become a scarce commodity.

Test

The YZR 500 handles really well and not just in the fastest corners like at the end of the main straight, where I could maintain an incredibly high shift speed after downshifting four gears quickly on the gearbox, everything by strongly squeezing the front brake lever to take advantage of the surprisingly powerful Japanese stainless steel brakes for this era. Kenny might not like them on long races, but for shorter track rides they work well. I am generally very critical of the brakes of the 70s, but not this time.

The OW48R immediately demonstrates its great maneuverability

The Yamaha also shifts very well from side to side in the chicane, where its low, compact design and short wheelbase of 1,350mm make it possible to quickly change direction with great ease and a lot of confidence. Despite being so short by later Grand Prix 500 standards, but also thanks to a low center of gravity, the Yamaha is also very stable over bumps..

While the rear monocross isn’t as smooth as modern rear suspensions, it offers a marked improvement over the twin shocks it replaces. Suzuki took a long time to offer its Flull Floater in response to the Yamaha mono-shock whose long nitrogen-charged DeCarbon element with its separate cartridge is fully adjustable in compression and rebound..

The YZR benefits greatly from its rear shock absorber, which is more efficient than the old dual elements.

Let’s come back to braking. Although the aluminum calipers only have two pistons each, the Yamaha stainless steel discs securely attached to their aluminum brackets surprised me both with their efficiency, as well as their initial response when touched to eliminate a little excessive speed in curves. Kenny Roberts’ insistence on maximizing front disc size surely plays a role here.

Oversized front discs take their toll on braking

Additionally, during the powerful braking required for the Assen chicane and again before the hairpin bend at the start of the layout, the brake-actuated hydraulic anti-dive on the Kayaba fork truly minimizes mass transfer using feedback. of the caliper to close a valve and increase the compression of the damping, thus slowing the frontal dive. Although KR Senior was not a big fan of the system, frequently opting for forks without anti-dive but with external damping adjustment, I found this to contribute to the feeling of stability the chassis provides. Yamaha, without causing the lack of sensation that most other systems of this type provide, where you no longer feel the front tire at all, because the hydraulics dampen the response of the front suspension too much by braking in a curve..

But there’s no denying that the OW48R’s engine doesn’t deliver the same powerful feel as the explosive engines of Kawasaki and Suzuki, even though the YPVS valve system helps maximize horsepower without doing so at the expense of handling..

The advantages of the cycle part make up for the lack of explosiveness of the engine

Just as KR will tell me later, I noticed that you could not open the throttle fully at low speed when coming out of a slow curve like the Assen Nationale Kurve, otherwise the engine is overwhelmed and had to hard to resume. On the other hand, it responds very well to the requests of the partially open accelerator from 6,500 rpm, but by making it turn above 8,000 rpm and maintaining its speed in curves we are rewarded with a good recovery, by the standards of the time, as well as a smooth transition to the top of the power curve, above 10,000 rpm. From there until the peak of 12,000 revolutions, the power increases quite sharply, but not in the same way as on rotary valve motorcycles, the acceleration is clearly more gradual, but necessarily slower..

The acceleration of line 4 is very gradual

In fact, Everett had 38mm Powerjet TZ500J carburettors installed on Roberts’ bike because they produce more horsepower in bench testing compared to the magnesium Flatslide carburetors that came with the bike, which are also much harder. to be adjusted correctly. But even with these, the Yamaha certainly wasn’t as fast as the ex-Ballington Kawasaki KR500 that Chris Wilson was riding on that I was going to ride later that same day. This genuinely narrow power curve means the pull-out box was a key part of Roberts’ championship success, with the art of configuring it perfectly for every circuit on an engine that has nothing left to give after 12,000 rpm..

Conclusion

Kenny Roberts really had to work hard to win the third of his world titles and the key to achieving that was the improved handling of the Yamaha OW48R. And even 40 years later, nothing has changed.

During the MotoGP era, Valentino Rossi and the now retired Jorge Lorenzo won a succession of world titles for Yamaha on a well-balanced YZR-M1 which, whether in 800 or 990cc, has always been more maneuverable than its Honda rivals. and Ducati without being so fast. So, just like today, the key element that allowed the YZR500 to clinch its last world title was the man who drove it: King Kenny, we salute you.

Kenny Roberts’ Yamaha YZR500 OW48R

Strong points

• Maneuverability
• Braking

Weak points

• Limited power
• Restricted power range

The technical sheet of the Yamaha YZR500 OW48R 1980

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