TORQUE
From copying a German DKW in 1955 to engineering one of the most revered two-stroke twins ever made — this is the full story of how Yamaha arrived at the RD350.
The four Japanese motorcycle manufacturers that dominate global roads today — Honda, Kawasaki, Suzuki, and Yamaha — are younger than they appear. In terms of motorcycle manufacture, all four are post-war creations, despite their parent companies having much older industrial roots.
Soichiro Honda built his first motorised bicycle in 1946. Kawasaki Heavy Industries only entered motorcycles in 1962, inheriting the Meguro factory when it acquired the struggling brand. Suzuki pivoted from textiles to two-wheelers in 1952. And Yamaha? Its story starts even earlier — but in a very different industry.
Torakusu Yamaha founded Nippon Gakki Co., Ltd. in 1887, initially to manufacture reed organs. The company grew into Japan's largest producer of musical instruments and later manufactured aircraft components during the Second World War. It was not until 1954 that Nippon Gakki decided to diversify into engine manufacturing, adopting the Yamaha name — after its founder — for this new venture.
The strategy they chose was pragmatic and widely used in Japan at the time: study the best-performing foreign designs and replicate them. It was not considered shameful. Honda did it, BSA did it, and the entire Japanese industry used reverse engineering as a shortcut to catching up with European competitors. Yamaha was simply the latest to follow the same path.
Yamaha's first production motorcycle rolled off the line in 1955 under the name YA1. It earned the nickname "Red Dragon" partly for its deep red colour, and partly because the engine was a meticulous copy of the German DKW RT125 — a single-cylinder 125cc two-stroke that had become the most widely copied motorcycle engine in history. BSA's Bantam was another copy of the same engine; Yamaha was in good company.
A year later, Yamaha repeated the formula with a 175cc version based on the DKW RT175. The foundations had been laid. The single-cylinder two-stroke philosophy would soon give way to something more ambitious.
The leap to a parallel-twin engine came in 1956. For the layout and architecture of this new motor, Yamaha looked to another German manufacturer: Adler, whose MB250 was an advanced but expensive two-cylinder two-stroke that the West German market had struggled to support commercially.
The new Yamaha twin was presented publicly as the YD1 in 1956. Yamaha engineered its own frame in-house, which was a meaningful step beyond simple copying. The engine, however, retained several characteristics of the Adler layout, most notably a secondary chain drive mounted on the left crankpin, and vertically-split crankcases — a design approach that would persist, largely unchanged, for nearly ten years.
A single carburettor fed both cylinders on the YD1. It was a compact, air-cooled layout that stripped away the rocker-arm front suspension and plunger rear suspension that Yamaha engineers disliked on the Adler, giving the YD1 a more modern road feel. Despite the conservative engine internals, the YD1 established the DNA of everything that would follow over the next two decades.
The YD series also spawned a competition offshoot. Races in Japan — steep hillclimb-style events known as the Asama races — led to the YDS1 under the YD series performance banner, and this bike eventually formed the basis for the TD1C factory racer.
By 1960, the YD series had found export markets. The YD2 was selling outside Japan — quietly, without making much noise — and Yamaha was learning what international riders expected. The answer came in 1964 with the YDS3, a model that addressed most of the shortcomings of its predecessors in a single revision.
The YDS3 introduced individual carburettors for each cylinder — a move that finally unlocked the full potential of the parallel-twin layout. The brakes were improved substantially, and the tubular steel frame was updated and derived directly from Yamaha's racing machines. The result sold well, particularly in the United Kingdom.
Alongside the YDS3, Yamaha also released a 305cc variant called the YM1, and a touring version of the YD3. The YDS3 remains historically significant as the last model built fully on the original Adler-derived concept. Everything after it represented a cleaner break.
The number four is considered unlucky in Japanese culture, so Yamaha skipped directly from the YDS3 to the DS5 in 1966. The DS5 brought two major engineering changes that had been overdue for years.
First, the clutch was moved off the crankshaft and repositioned on the primary gearbox shaft. This eliminated a source of persistent mechanical grief that had afflicted every model back to the YD1. Second, cast-iron cylinders were replaced with aluminium — lighter, better conducting, and more appropriate for a performance-oriented engine. The DS5 also gained an electric starter, a first for this family of bikes, though it proved unreliable in practice.
The large crankshaft assembly caused vibration that wore bearings and engine casings prematurely. Despite these problems, the DS5 engine fundamentally delivered strong performance. Its successor, the DS6, was the final evolution of this generation — every last engineering possibility of the YD1's crankcase concept had been used up.
While the DS6 squeezed the last performance from the old design, Yamaha's engineers were working in parallel on an entirely new architecture. In 1967, they unveiled the R1 — a 350cc parallel twin with horizontally-split crankcases, a labyrinth crankshaft seal, and aluminium cylinders. The bore and stroke dimensions were 59.6 × 61 mm — different from the 54 × 54 mm that would later define the 250/350 racing and touring family.
The R1 was a revelation. Concerns about cooling a 350cc air-cooled two-stroke had made engineers cautious, but the bike performed beyond expectations. Its 1968 successor, the R2, was never officially sold in many markets, but it remains personally regarded by many historians as the finest two-stroke Yamaha ever made — characterised by straight exhausts and a headlight with an integrated instrument cluster. The R3 followed with five-port cylinders and twin clocks, but a new 350 was already on its way.
On the 250cc side, the DS6 concept was replaced by the DS7 — a properly modern machine with horizontally-split crankcases, a 54mm stroke crankshaft, and aluminium cylinders. The DS7 was widely considered a superb road bike and, together with the R5, represented the pinnacle of Yamaha's two-stroke knowledge at the start of the 1970s.
In the early 1970s, Yamaha made one decisive mechanical change to both the R5 and DS7 families: reed valves were added to the intake systems. This single modification transformed the low-end throttle response and broadened the power band considerably. To reflect this fundamental change, both model families were renamed under the new RD designation — Racing Development.
The Yamaha RD350 entered production in 1973 and remained in the lineup through to 1975. Evolved from the R5 — itself a 350cc, 5-speed bike with a piston-port engine and front drum brakes — the RD350 introduced a 6-speed gearbox, a reed-valve intake system, and Yamaha's Autolube automatic oil injection, which mixed two-stroke oil directly at the carburettor inlet and eliminated the need for pre-mixed fuel.
The engine was a 347cc air-cooled parallel twin producing 32–39 horsepower at 7,500 rpm depending on market specification. The frame geometry borrowed directly from Yamaha's TZ250 and TZ350 racing bikes, with a 27-degree fork rake that gave the RD350 handling characteristics well beyond what its modest displacement suggested. Braking was handled by a single front disc — advanced for the class in 1973 — paired with a rear drum.
Available in dark green, brandy red, or purple with contrasting panel graphics, the RD350 rode on 18-inch chrome wire-spoked wheels (1.85-inch front, 2.15-inch rear in most markets). The UK received narrower 1.60/1.85-inch rims. At 152 kg wet, it was genuinely light, and the torquey reed-valve engine made it feel faster than the numbers suggested. Contemporary road tests consistently praised the RD350's ability to embarrass much larger and more expensive machinery in real-world riding conditions.
The RD350 laid the groundwork for four further model years of development. In 1976, Yamaha introduced the RD400C, followed by the RD400D, RD400E, and finally the RD400F in 1979 — the last air-cooled RD to be sold new. These later models progressively refined the design to meet tightening emissions regulations, primarily in North America, and in doing so reverted to manual oil-and-petrol premixing rather than Autolube. Power outputs were modestly reduced from peak RD350 levels, though handling and braking continued to improve.
Throughout this period, the RD family held its own against formidable competition. The Kawasaki H2 750 triple offered more raw power but was notoriously difficult to handle. The RD400's strength was balance — tractable power, precise handling, and a nimbleness that heavy triples could not match in the real world.
The final major chapter in the air-cooled RD story was closed in 1978–1980 when Yamaha applied liquid cooling to the 350cc two-stroke twin and introduced the RD350LC (Liquid Cooled). The LC was a significant engineering step: water cooling allowed tighter thermal control of the cylinders and head, enabling more aggressive porting, higher compression, and a broader, stronger power band than any air-cooled RD had been able to achieve.
The RD350LC and its YPVS (Yamaha Power Valve System) equipped successors — introduced in the early 1980s — pushed the small-displacement two-stroke concept as far as road regulations would allow. They remained competitive, fast, and deeply loved right through until emissions legislation brought the two-stroke era to a close in most markets.
While the global RD story wound down, a parallel chapter was unfolding in India. The Rajdoot 350 — manufactured by the Escorts Group under licence from Yamaha — entered production in 1983 based on the RD350B architecture. It was sold under the Rajdoot brand name and represented a rare opportunity for Indian enthusiasts to experience genuine two-stroke performance during a period when the domestic market was otherwise limited to small-displacement commuters.
Two variants were produced: the High Torque (HT) at 30.5 bhp, and the Low Torque (LT) at 27 bhp — both detuned from the original RD350B's 39 bhp to suit Indian fuel quality and improve fuel economy. The High Torque model was capable of 160 km/h and could reach 60 km/h from rest in approximately four seconds, making it by far the fastest production motorcycle available in India at the time.
However, the Rajdoot 350's fuel thirst worked against it in a market where economy was paramount. The Low Torque version, launched in 1985, attempted to address this — but by then, a new generation of fuel-efficient four-stroke commuters was arriving from Hero Honda and others. Production of the Rajdoot 350 ceased in 1990, by which point the bike had been almost entirely indigenised with minimal imported Japanese components.
Despite its commercial struggles, the Rajdoot 350 was ranked among the top 10 motorcycles of the century by Cycle World USA — a testament to the fundamental brilliance of the RD350 platform regardless of market specification. Today, well-maintained examples command significant prices among Indian collectors, and a thriving restoration community keeps the HT and LT variants alive across the country.
The thread running from Torakusu Yamaha's 1887 organ factory to the RD350's screaming reed-valve twin is, at first glance, a strange one. But the logic is consistent throughout: identify the best available technology, understand it completely, and then improve on it. The YA1 was a copy. The YD1 was an adaptation. The YDS3 was a refinement. The R5, DS7, and RD350 were original machines that left every model before them behind.
That is how the world's largest musical instrument manufacturer became the builder of one of the most celebrated two-stroke motorcycles of the twentieth century — one that still commands respect, restoration budgets, and open throttles on twisting roads more than fifty years after it was first designed.
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