1973 YAMAHA RZ Twin Rotor RZ
1973 YAMAHA RZ Twin Rotor RZ Atlas Editions Classic Motorcycle card
Unrealized expectations
In the early 1970s, the entire automotive industry and engine manufacturers worldwide had high hopes for the Wankel rotary engine. The motorcycle sector, which had just enjoyed a phenomenal growth rate, wanted to make the most of this unorthodox power unit.
Astounding Prototypes
Yamaha, which was hopeful of catching and beating the industry giant Honda, investigated every technological avenue that might help the company achieve its ambition and in the process built some astounding prototypes. After a fuel-injected four-cylinder two-stroke shown at the 1971 Tokyo Show, Yamaha unveiled the rotary-engined RZ 201 in 1973.
Age-Old Problem
The rotary engine seemed to be the answer to the problem that had plagued engineers for centuries: how to translate the up-and-down, straight-line motion of a piston into a smooth rotation. The basic principle of the engine, developed by German Dr. Felix Wankel, was simple – a three-sided rotor with curved edges turned about a geared shaft within a specially shaped housing, exposing spark plugs, and intake and exhaust ports and forming combustion chambers against each face. Theoretically, the “suck-squeeze-bang-blow” four-stroke cycle occurred on every revolution, providing a constant power stream. In principle, the development program was long, complicated and costly. There were two fundamental problems: how to keep the rotor tips gas-tight and how to cool the engine. The Wankel engine used more fuel and emitted more pollutants than a conventional engine. The combination of the tough anti-pollution laws in the US and the mid-1970s gasoline crisis killed Yamaha’s Wankel program and the RZ 201 project.
SPECIFICATIONS
Engine: 720cc (equivalent) water-cooled twin rotor Wankel rotary four-stroke
Power Rating: 68 hp @ 6500 rpm
Valves: ports exposed by three-lobe rotor
Transmission: primary drive by gears, chain final drive
Suspension: telescopic forks (front); swing arm with twin spring/dampers (rear)
Brakes: twin discs (front); disc (rear)
Weight and Speed: classified
Unlike the Sachs-Hercules and the Suzuki, this superb Wankel-engined grand touring bike never got past the prototype stage.
Card number D2 77-01
