Yamaha Rising, Part 3 - CLASSICS REMEMBERED

A look back at the Yamaha RD56 factory roadrace bike

In the Japanese recession of 1962, Yamaha did not race and in fact had to close its Technical Laboratories. Despite this, a more powerful 125, the RA55 of 56 x 50.7mm bore and stroke, was now developed, making 22 hp at 10,500 rpm. It has been called "a test bed for the RD56." The 250 RD48 now received a third transfer port in each cylinder, raising its power to 42 hp. In photos RD48 is seen with that era's state-of-the-art rear suspension: Girling units. In the mid- to late 1950s British riders hired by Italian makers brought Girlings with them in their luggage (to protect them from the pogo sticks some makers used as suspension). Norton, backing the engineering of the McCandless brothers in 1950, had shown what the full package of twin-loop chassis and hydraulic-damped telefork and swingarm suspension could do. Oddities such as sliding-pillar and leading/trailing-link had by 1958 finally been given up by motorcycle designers. Although Japan was half a world from the Europeans GPs, you can be sure Yamaha engineers availed themselves of every information source—especially the German engineers with whom they began consultation in the 1950s.

To overcome spark-plug fouling it was necessary to make engines cool adequately without need of running over-rich. All manufacturers had tried closer-pitch finning to reduce cylinder temperature, but at racetrack speeds there was not enough RAM pressure to push air through the tighter fin space (Kawasaki would have the same experience with coolant radiators in the late 1970s). Yamaha's next step was to replace the inconsistent and seizure-prone anodized cylinder technology.

In 1955 Moto Guzzi had saved weight on its 350 horizontal single (five world championships, 1953–'57) by eliminating its heavy iron cylinder liner, instead plating hard chromium directly onto an aluminum bore. A positive side effect was that improved piston cooling (iron, although an excellent wear surface, has only one-third the heat conductivity of aluminum alloys) allowed use of closer piston clearance. Around 1960, Porsche in an F1 design adopted a dimpled chrome-on-aluminum bore. Yamaha now adopted a type of chrome plating made oil-wettable by reversing the plating polarity to etch myriad cavities in the surface. Today, cylinder bores coated with Nikasil or other hard surfacing has become normal for production engines.

While continuing some RA41 features that would soon be dropped (dual rotary valves, the two-ring piston) RA55 added others. In 1959 Walter Kaaden at MZ had added to that maker’s race engines Richard Kuchen’s third transfer port, used by Zundapp to break DKW’s Schnuerle patent. It was located opposite the exhaust and aimed steeply upward at roughly 60 degrees. This port had been added to the 250 twin RD48 and now became a subject of RA55 development, boosting power to 22 hp at 10,500. If total transfer port area is too small, the jets of fresh charge entering the cylinder move so fast that they quickly reach the exhaust port. By adding the flow area of this third port, Yamaha reduced transfer velocity so that a greater volume of charge was present in the cylinder at the moment of exhaust closure.

Use of a single compression ring is not a new practice, for power is consumed in sliding any piston ring along the viscous oil film that supports it. That’s why many four-stroke racing pistons have just one compression ring plus an oil scraper. Production engines, which must last thousands of miles, are given two compression rings because they maintain a good seal for longer but at the cost of extra friction. Oil scraper rings have no purpose in a crankcase-scavenged two-stroke, so the best choice for short-term high power is a single ring.

The next step in 250 development was the RD56, ready at the end of 1962. It was of 56 x 50.7mm dimensions, a parallel twin with side-mounted M34 carburetors. Fumio Ito rode it into third place in November at the “First Suzuka All-Japan Road Race.” In April 1963 he won the non-point Malaysian GP. This bike had an all-new chassis made by Kuromori and clearly derived from the 1950 McCandless twin-loop Norton chassis now remembered as “the Featherbed.” Its 220mm front brake featured two panels and four leading shoes. Wheel size was 18 inches as before, with tire sizes 2.75/3.00 F/R. To us in 2017 these tires appear tiny, but the universal experience of GP racers had been that the larger the tires, the lower the top speed. Today’s GPs often take place on twisty “bull-ring” courses like Valencia, which emphasize maximum turning ability. But nearly 60 years ago many courses had long straights where extra top speed made a real difference. Examples are Monza, the TT, and Belgium’s Spa-Francorchamps.

Continuing development brought higher-volume exhaust pipes, which extracted more energy from the exhaust process, applying it to the twin tasks of (1) providing low pressure at the exhaust port to speed cylinder refilling and (2) then sending back a return positive wave that not only stopped loss of fresh charge out the exhaust but also by stuffing some lost charge back in acted as a weak supercharger. The third transfer port had now become large enough to require a divider to support the piston ring, and total cylinder and head fin area had been increased. Now the new twin was making 47 hp at 11,000 on a 25:1 oil ratio plus Autolube with seven branch lines (including one to each rotary valve case). A 7-speed vertically-stacked gearbox was provided.

Yamaha’s first GP of 1963 was the Isle of Man. Ito demonstrated the new reliability and speed of the RD56 by leading the 250 TT for a time, then finishing the 226-mile event second by 27 seconds to Jim Redman on Honda-4. The “Honda wall” had nearly been penetrated! Hiroshi Hasegawa on another RD56 was fourth, ten minutes back. This was a solid achievement, for it proved that Yamaha’s maturing technologies of developed piston and cylinder metallurgy plus chrome-plated cylinder wall had made the two-stroke a formidable opponent for Honda’s high-revving four-strokes. The new engine had what had been missing since the beginning—thermal toughness—the ability to run seizure-free for hours at high power, in the variety of conditions present in a long race.

MZ’s Walter Kaaden had shown what two-strokes could do by combining the resonant “counter-cone” exhaust pipe of Erich Wolf (DKW (1951–’52) with ever-taller exhaust ports. His thoughtful work was limited by East Germany’s commercial isolation and weak postwar economy. Further progress now required modern industrial power—rows of dyno cells served by uniformed technicians testing and reporting on scores of different cylinder portings, piston and cylinder alloys, and exhaust pipe shapes.

None of this would have been possible had Yamaha not been highly successful in promoting and selling its products. Its methods would make it one of the Big Four Japanese motorcycle manufacturers to survive out of the 250-odd makers who operated in the early-to-mid 1950s. Rows of Meidensha dynamometers and teams of graduate engineers cost money that can come only from a profitable sales base (by 1970 Yamaha’s annual sales would reach 570,000). Much is made in racing of the romance of substituting brilliant ideas for money—“winning on a shoestring.” The contrasting experiences of MZ and Yamaha reveal the truth. MZ’s ideas could win GPs but not championships.

Next was the Dutch TT at Assen, where Ito again finished second to Redman, with Sunako fourth behind Provini’s remarkable Morini single.

In Belgium came full vindication of Yamaha’s work—its first Grand Prix win and a 1-2 finish by Ito and Sunako, comfortably clear of Provini in third—and the howling pack of Hondas.

Yamaha now hired English rider Phil Read. At the Suzuka Japan 250GP Yamahas finished second and third, with Read relegated to third by a fouled plug. Ito was second.

In 1964 the further-developed RD56 won six 250 GPs and Phil Read was champion over Redman (Honda) and the hard-riding Alan Shepherd (MZ). Honda, by now the world’s largest motorcycle manufacturer, responded in the only way possible: by seeking to operate at rpm out of reach of their existing four-cylinder 250s. The tool for this was the six-cylinder, introduced in haste at Monza, where it seized. Its development and success would take time, competing for R&D resources with Honda’s entry into large-scale automobile production.

The following year RD56 Yamahas—now making 54 hp—won eight GPs (two by Canadian Mike Duff) and Read was champion again. More power would be needed to compete with Honda’s 250-6, but to make it reliably, an even higher level of piston temperature control would be necessary: water-cooling.

Related: