Yamaha Rising, Part 1 - CLASSICS REMEMBERED

A look back at the Yamaha RD56 factory roadrace bike

1965 yamaha rd56 static 3/4 view
1965 Yamaha RD56By Rikita (Own work) [CC BY-SA 3.0 or GFDL, via Wikimedia Commons

Yamaha became a world power in motorcycling when on July 7, 1963, Fumio Ito won the Belgian 250 GP on the very fast Spa-Francorchamps course, averaging 115.487 mph. Second was Yasukazu Sunako. Both men were mounted on Yamaha’s RD56 air-cooled two-stroke twins. Behind them were the legendary Tarquinio Provini on Morini (this was the year when Provini came so achingly close to edging out Honda for the 250 championship) and the factory Honda fours.

It almost didn’t happen. In practice, the Yamahas accelerated strongly to about 130 mph then went into fuel starvation as vibration affected the remote float bowls of the machine’s M34 carburetors. In creative desperation, the crew cobbled on a second pair of bowls, one behind each sideways-projecting carb (these were rotary-valve machines with lateral fairing bulges enclosing the extra width of their intake systems). With full fuel flow, the Yamahas could now reach 145 mph.

On that day in the 500 class, Mike Hailwood’s winning MV was only 8 mph faster. With the new Japanese factories pouring R&D into 50, 125, and 250 racebikes, and with only MV continuing to build for the 500 class, the FIM would soon be considering dropping the big class “for lack of interest.” In this era, the real excitement was not in how badly the MV-4s would outrun a collection of thudding Norton and G50 singles (whose production ended that very year) but in the soaring rpm and lap speeds of the dramatic new 250s.

Among Japanese makes, Yamaha was the newcomer and Honda the old hand, having first raced in a GP four years earlier. In 1961 Hailwood had given Honda its first 250 championship, and by the end of 1963 Jim Redman would give the brand two more. While Honda’s 250 made roughly 45 hp at this point, Yamaha had somehow achieved high-speed reliability at close to 50 hp. The flexibility of Honda’s 14,000-rpm four-valve four-strokes gave them advantages in early acceleration off corners, but the sheer power of Yamaha’s fast-developing two-stroke was unmatched. Englishman Phil Read would win the next two 250 titles for Yamaha on the RD56.

Back in 1921 Nippon Gakki, the musical instrument company from which Yamaha Motor would emerge, took up the manufacture of laminated wood propellers for aircraft. Ten years later the company added specialized machine tools and foundry facilities to begin making the new variable-pitch metal props. When World War II ended, the machine tools of Japan’s former war industries were impounded until 1952. Yamaha’s new president Genichi Kawakami had to decide “what is to be the company’s next area of business” when the end of impound released their equipment. Many products were considered, including sewing machines or three-wheeled trucks, but the choice fell upon motorcycles. Kawakami said, “I want to carry out trial manufacturing of motorcycle engines.”

Like other Japanese companies, Yamaha sent engineers to Germany, whose booming motorcycle factories were in the early 1950s producing hundreds of thousands of NSUs and DKWs. They also traveled to the US and elsewhere to study production methods and acquire machine tools.

DKW RT125 static side view
DKW RT125By Huhu Uet (Own work) GFDL or CC BY-SA 3.0, via Wikimedia Commons

DKW’s RT-125 was chosen as the model for the first Yamaha. Prototype work began in October 1953 but was not easy; piston seizures required achieving detailed understanding of iron and aluminum metallurgy. Management knew that breaking into Japan’s crowded motorbike market would require stand-out quality and reliability, but Yamaha lacked a test track. Road testing took its place—the so-called “Miyaguchi test” of 10,000 kilometers over poor roads.

“The new bikes were hit by piston seizures even after [only] a small distance had been covered,” wrote former director Tomoo Sugiyama in his 1978 historical review.

This forced a rapid pace of metallurgical development—a race to develop pistons that combined mechanical strength with a controlled rate of thermal expansion.

Everything happened extremely fast: getting the first Yamaha into production (December ’54) and sale (February ’55)—the “Aka-tombo” or “Red Dragonfly” 125—producing special bikes to win in the 1955 Asama and Fuji roadraces, driving spare engines across Japan overnight, and running dynos in cool air available only at midnight required everyone to work all hours. President Kawakami and top engineering and production executives were not men in lint-free suits protected from reality by big desks; they did test riding and assembled engines themselves to better understand the real nature of the problems they faced.

A 1957 production license for the German Adler twin (yes, the company that made typewriters) gave Yamaha a starting point for their own YD 250 twins. A year later, a racing version of the YD twin was sent with Fumio Ito to race on Catalina Island off California. Ito brought the high-revving twin home in sixth.

Yamaha’s success in domestic races exposed its engineers to other ideas. The Showa Company’s design chief Masayasu Nakamura had built a rotary-valve 125 racer with strong performance and had introduced reed valves to Japan in 1956. Yamaha bought the company in 1960.

For racing, Yamaha had quickly moved beyond the iron cylinder of their 125 single to the improved cooling of iron-linered aluminum cylinders on its 1959 YDS1-R twin racer. As the company pushed horsepower upward, heat set a limit. The two-stroke’s weak point is high-piston temperature. Two-stroke pistons are heated by combustion twice as often as four-stroke pistons, so they run hotter. Get them hot enough and the result is detonation. In 1965 I wondered why the crown edges of my Yamaha TD1-B’s pistons were smooth when new but often became as rough as files after some running. Mysterious holes—sometimes as deep as 5mm—were eroded into cylinder heads right at the edge of the head gaskets. What I was seeing was an effect of detonation, a violent abnormal combustion capable of eroding solid metal from pistons and cylinder heads.

Reaching planned engineering, production, and sales goals all had to happen at once in this period. As engineer Hiroshi Naito would say of that time many years later, “Lights on all night.”

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