Classic Bike (UK) - - Contents -

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.


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,


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.

Two RZ201S were built: this one and a red one with a black seat

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