Yamaha RZ201 Rotary Concept
Yamaha RZ201 Rotary Concept | |
Manufacturer | |
---|---|
Weight | |
Manuals | Service Manual |
Photos
Overview
Yamaha RZ 201 Rotary Concept
Yamahas rotary motorcycle RZ201 was unveiled on the 19th Tokyo Motor Show in 1972 and surprised even many employees from the company, as most were totally unaware of this project.
The machines cycle characteristics were developed together with those of that other bombshell, the GL750 4-cylinder 2-stroke and the production machine TX750. The RZ201 had a wheelbase of 1.485 cm compared to 1.455 for the TX750. Weight was 220 kg against 230 kg respectively.
The rotary had the internal project code YZ587 and the design sketches were approved by August 22, 1972. The Yamaha rotary engine utilized CCR/OCR (charge cooled rotor, but also oil-cooled rotor) The rotors had a radius of 83 mm and a diameter of 56 mm, resulting in a 660 cc displacement. Performance was 66 hp @ 6.000 rpm, comparable to the TX750s 63 hp @ 6.500 rpm, (bore x stroke 80 x 74 mm).
As ignition Yamaha already used a full CDI system and most of the novel electrics used on the TX750 were also applied. An electric starter motor was also added.
A few RZ201s were hand-made and according to some sources, 1 or 2 are still "hidden" in the factory to be discovered!
Yamaha Circuit
Magazine. August 1981
Journalists too were drawn
to the Yamaha stand by this unique model and motorcycle newspapers the
world over proclaimed that its introduction marked the dawn of a new era
in motorcycle design.
The RZ201, however, was
never intended as a production model. It was simply an exhibition
machine aimed at demonstrating the diversity of Yamaha technology. The
fact that the machine was built to such a high standard of both
technology and design fooled the motocycle world into believing that it
was a production prototype.
The rotary piston engine was developed by Yamaha along with Yanmar
Diesels who had already obtained a licence to manufacture marine and
light vehicle engines from the German patent holders NSU
Working within the confines of their patent licence, Yamaha came up with
several technical innovations, all designed to make this type of engine
suitable for motorcycles. The twin rotary pistons, each displacing 330cc
rotated in the direction of the vehicle advance to alleviate any vehicle
roll caused by engine torque. The inlet and exhaust ports and the
ignition plug were re-arranged in a more rational lay-out than the
original design, saving a great deal of time and expense when carrying
out routine maintenance. Another ingenious device was the combination
port system that featured a periphery port working in conjunction with a
side port. The combined effect of these two ports was to increase
combustion efficiency over the low speed range while improving intake
efficiency at higher speeds, giving improved performance throughout the
rev range.
The final version of the
rotary engine developed 68ps (Hp) at 6500rpm with a maximum torque of
7.8kgf-m at 4000rpm, and this power output was coupled to a
five speed gear box and transmitted to the rear wheel
by a silent chain.
A liquid-cooling system was adopted for the RZ201, while another
technical innovation from Yamaha took care of engine lubrication. This
was the "Charge Cooled Rotor" system which fed oil directly into the
mixture from the carburetor to lubricate and cool the rotors. This
system, which did away with the oil cooler required on conventional
rotary engines, helped to make the power unit narrower, and so more
suitable for use in a motorcycle.
it would have made a
striking addition to the Yamaha range, and possibly sparked off a
revolutionary new approach to motorcycle design. As it turned out, the
Yamaha research and design department moved on to other things and, even
without the help of the rotary engine, have kept the name of Yamaha to
the forefront of motorcycle design.