LOST YAMAHA PROTOTYPE
The spotlight falls on the rotary-powered RZ201 – it caused a sensation at the 1972 Tokyo Show, but never made production
During the early ’70s the Japanese ‘big four’ were engrossed in a race to create the ultimate ‘flagship’ – a motorcycle that riders around the globe looked up to in awe, and a machine which would lead consumers to buy their more popular smaller bikes. Honda had the CB750, Suzuki sold the GT750 water cooled two-stroke triple, and Kawasaki built their H2 and Z1. In 1970 Yamaha broke their two-stroke tradition by launching the four-stroke XS1 650cc twin. Then, as we recalled in the February issue of Classic Bike, came the advanced water-cooled Yamaha GL750 four-cylinder two-stroke, launched a blaze of publicity at the 1971 Tokyo Motor Show. A year on, Yamaha dropped another bombshell by revealing the Yamaha RZ201 twin rotary at the 19th Tokyo Motor Show, held from October 23 to November 5. The RZ201 rotary project was started in February 1971, with development undertaken in utter secrecy (internal project code YZ587) and without the knowledge of Suzuki, who were experiencing difficulties in making their own rotary-powered bike.
At that time, rotary engines were considered the next big thing on both four and two wheels. However there were many problems to overcome for a motorcycle rotary. The first step was to buy a license for development from rights-holders NSU, which Suzuki had done on November 24, 1970 (for 62-75hp petrol motorcycles) and assumed they were the only Japanese manufacturer developing a rotary-powered motorcycle for mass production. They received the shock of their lives when Yamaha stole the show with the revolutionary RZ201 at the 1972 Tokyo Motor Show! Unknown to Suzuki, Yamaha had been working with Yanmar, a Japanese marine and small engine builder which, since 1961, had held the rights to build 76-104hp rotary petrol engines and 1-300hp diesel powered rotaries. To make matters worse, the new RZ201 had two rotors – one more than the technically simpler Suzuki RX5/RE5. And, to rub salt into the wound, the RZ201 was a production-ready runner, not just a prototype.
When I was originally researching the history of the RZ back in 2009, I was in regular contact with a guy called Sam Costanzo (the founder of rotaryrecycle.net) who told me his day job was going around Suzuki Dealers in the USA and buying up their old RE5 parts. He once worked for Wankel and later Suzuki, so he was ‘on the ground’ at the time of the RZ and had a couple of friends at Yanmar. Sam was at the Tokyo Motor Show for the launch of the RZ and had written up a handy account, which I think he published on his Rotary Recycle website at the time. He also couriered me a large box of information, which I copied and returned. Unfortunately, Sam passed away not long after. He had told me the RZ launch was a lavish affair. He said: “The Yamaha stand had a roped-off display with a sign saying: ‘special sneak preview unveiling at 12:00pm’. At 11:45am reporters were gathering around the revolving Yamaha display. At precisely midday, the strobe lights went on and fanfare music started to play, the hype instantly attracting a large crowd. Two shapely models came out and slowly walked around the display, pointing to mysterious bulges beneath the covers.
“This increased the mystique another notch and drew the crowd in closer. The two models stepped back and clapped their hands loudly. At that moment, all the covers on the display lifted straight up, unveiling the new Yamaha RZ201 Twin Rotor motorcycle!
“The bike was a beauty! Camera flashes lit up like Roman candles. Slowly revolving around, the overhead lights reflected the rich metalflake cinnamon brown-coloured tank, accented by twin white stripes with a matching contoured tan leather seat. The lower lights highlighted the radiator and showed off the triple-plated chrome radiator guards, twin mufflers, side covers, fenders and wheel rims. The Yamaha Twin Rotary was absolutely outstanding and stole the show!”
According to Costanzo, a Yamaha representative explained details and specifications to the large crowd, revealing that Yamaha had been developing it for year – and stressed that the RZ201 was a fully working and operational twin rotary that had been tried and tested, was scheduled for full production and would be available at all Y by mid-february... and that orders were now being taken!
The models handed out press release bags with colour photos, a facto pricing sheet, a large RZ201 wall poster and a calendar. “Plus, an RZ201 order form,” Costanzo reflected.
The bike was showing signs of front disc wear, so this was no prototype launch. At the show, Yamaha said it would produce 1000 units per month for 1973 – US dealers later advertised for people to come into their showrooms and see the new bikes!
But, as Yamaha was discovering, building a practical and reliable rotary engine was no easy task – especially for a motorcycle. Rotary engines get very hot on the combustion side, yet cool on the intake side, so rotor cooling is required as well as water cooling. In car rotaries, shaft-bearing lubricating oil is pumped through the rotor to extract heat – this is called an Oil Cooled Rotor (OCR) system. The Yanmar/yamaha water-cooled rotary used a lubrication system that resolved the overheating rotor problems. Yamaha called this CCR – Charge Cooled Rotor. The engine rotor was also cooled by the incoming charge while entering the combustion chamber, and the side ports provided passage for the fresh charge through the rotor.
‘THE WATER-COOLED 660CC TWIN-ROTOR ENGINE PRODUCED A HEALTHY 68HP AND 56.4LB FT’
Using Yamaha’s two-stroke-derived Autolube system, the CCR system pumped oil directly into the incoming fuel/air mixture from the two Keihin CV carburettors (Mikuni VM34S were also used at different times) to lubricate the rotors and control internal heat levels. However, this system created a two-stroke-like exhaust smoke residue – at a time when visible emissions had become highly unwelcome in the US.
A single spark plug was used instead of the conventional twin-plug arrangement, while an electronic CDI with a single coil per rotor took care of spark timing. A triple chain system mounted on the left side of the rotors drove the wet clutch and five-speed gearbox. The water-cooled 660cc twin-rotor engine produced a healthy 68hp (only 2hp less than the 1971 GL750) with a strong torque rating of 56.4lb ft at 4000rpm. Weighing in at only 210kg, the RZ201 was 20kg lighter than the 62hp, 497cc Suzuki RE5 when the latter was released in 1974, as well as being considerably more powerful. With three power strokes per rotor, it was also silky smooth. Importantly, the engine rotation on the RZ201 was the same as the wheel direction, thus eliminating side-to-side torque-induced reaction of the bike when the throttle was opened and closed. To create the RZ201, two of the four Yamaha GL750S built the previous year were used as donor motorcycles by the R&D Department. By now, a decision had already been made not to produce the awe-inspiring four-cylinder two-stroke GL750 due to strict future US emissions laws, and nothing was sacred at the time when the R&D team needed parts for Test and Acceptance (T&A).
The two chassis were modified to house the rotary engine with a steeper steering rake than the GL750 for sporty riding. Yamaha also wanted greater high-speed stability, so the RZ201 wheelbase was increased by 35mm to 1485mm. Many GL750 parts were retained – an exception being the addition of a rear disc brake to replace the GL750’S drum brake, although it retained twin-disc front brakes. Yamaha built one deep-maroon RZ201 sporting a red seat, and a red bike with a black seat, both with revamped GL750 instrument packages, but larger radiators. The RZ201S also enjoyed heavy-duty Takasago alloy H-section race wheel rims. Yamaha and Yanmar were planning to establish a joint venture to produce the engines in a new Yamaha plant.
Costanzo recalled: “All eyes were looking towards mid-february, when the RZ201 would hit the Yamaha showrooms. But February passed and no RZ201S were seen anywhere. On May 1, 1973, Yamaha issued a press statement that the RZ201 would not be available until mid-august due to assembly-line teething problems. By late August there was still no sign of RZ201 activity.” Rumours circulated regarding the delay.
So what went wrong? Yamaha’s ‘apparent’ licence was very limited, regarding where they could sell their bikes. Perhaps Yamaha were planning on getting worldwide rights,
‘TO CREATE THE RZ201, TWO OF THE GL750S BUILT IN 1970 WERE USED AS DONOR MACHINES’
which wouldn’t be surprising considering they planned to build 1000 units a month. Or maybe the RZ201 was never put into production because of the upcoming American Environmental Protection Agency (EPA) emissions laws – the same reason that the GL750 project was stillborn. The US ‘Muskie’ Bill was presented in 1970, stipulating tight standards to be met by 1975. Hydrocarbon emissions were the problem, and most two-strokes were well above the limit, so it’s possible the oilburning RZ201 was also canned as a result. We know the RZ201 engine actually ran, but maybe it was never fully developed and, with such a restricted market and therefore lower return, Yamaha pulled the plug? All rotary R&D work was channelled back to NSU Wankel for all licence holders to mutually benefit, so NSU Wankel may have looked unkindly upon the secret Yanmar/yamaha joint effort.
Costanzo added an important angle: “Yamaha applied for a licence, hoping that NSU Wankel was hungry for another $20-$30 million. However, since Yanmar held the licence to manufacture the horsepower range for petrol and diesel (76-104hp), they could not issue another licence for the same horsepower. Yamaha did not gain a licence – they were professing that they had one. What they were hoping for was to actually team up with Yanmar and skirt around it.”
But Yamaha’s interest in rotaries was still evident a year after the ’72 launch. Australian Rod Tingate briefly worked for Yamaha Amsterdam and recalls crating up a Yamaha-purchased Sachs-hercules W2000 and sending it off to Yamaha Japan around Christmas 1973. Technical manager Mr Tamada was so anxious for a W2000 that, by mistake, he asked three people – Ludy Beumer, Jacek Skibinski and Bob van der Zijden – to buy one. Beumer recalled: “We each dutifully purchased one from different sources – one was sent to Japan, and the other two were scrapped.”
The RZ201’S demise may be due to one or a combination of reasons. In fact, Yamaha recently claimed it didn’t reach production due to its very high fuel consumption. Mr Hiroshi Sasaki from the Communication Plaza (Yamaha museum), Yamaha Motor Co Japan, said: “Fuel consumption and emissions were an important item in those days, as today. That project was stopped in 1975.”
Whatever the reason, Yamaha went on to successfully re-focus its efforts towards four-stroke road bike development and two-stroke race bike superiority.