Classic Bike (UK) - - Contents -

Yamaha’s lost two-stroke four pro­to­type

Dur­ing the early 1970s Yamaha en­joyed an en­vi­able rep­u­ta­tion for pro­duc­ing sporty mid­dleweight road and race twin-cylin­der two-stroke mo­tor­cy­cles. It had dom­i­nated Grand Prix road rac­ing and was on the cusp of im­ple­ment­ing a host of new tech­nolo­gies that would carry its two-strokes well into the fol­low­ing decade. Un­veiled at the 18th Tokyo Mo­tor Show in 1971, the tech­ni­cally-ad­vanced GL750 , wa­ter-cooled, four-cylin­der two-stroke stole the show. It bris­tled with fea­tures never be­fore seen on a Ja­panese road bike – the al­ter­na­tor mounted be­hind the crank, reed­valve in­duc­tion, twin-disc front brakes and fuel in­jec­tion – and was ten years ahead of its time. It could well have changed the face of mo­tor­cy­cling, so it’s easy to un­der­stand why the op­po­si­tion cow­ered at the mere thought of this bike hit­ting dealer floors – they could see the po­ten­tial of it sweep­ing big-bike sales.

But it never hap­pened. Yamaha qui­etly canned the project and 12 months later cre­ated an­other storm at the same show with its RZ201 twin-ro­tary con­cept. In the mean­time, an all-new TX750 four-stroke par­al­lel-twin was an­nounced in Septem­ber 1972, and the GL750 was quickly for­got­ten in a myr­iad of new releases.

Dur­ing ’71 the de­ci­sion had been taken by Yamaha’s Tech­ni­cal Di­vi­sion to de­velop a four-cylin­der ma­chine, co­de­named YZ401. Hiroshi Sasaki from the Com­mu­ni­ca­tion Plaza (Yamaha mu­seum) says that re­tired Chief Engi­neer Taka­hasi Mat­sui told him that “one aim was to re­spond to the big mo­tor­cy­cle boom in Europe and Amer­ica, and the other was to make a base ma­chine for the Day­tona 200.”

Although not di­rectly in­volved with the GL750 project, Head of Team Hiroshi Naito and Mat­sui-san de­vel­oped the OW19/TZ750A (co­de­name YZ648) and 500cc OW20/ YZR500 (co­de­name YZ648A) rac­ing pro­to­types – projects which con­cur­rently started a cou­ple of months later in May 1971, af­ter the GL750.

For the GL en­gine, Yamaha joined a pair of ex­ist­ing twin-cylin­der cranks from the

Crowds swarmed the GL at the 1971 Tokyo Mo­tor Show

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