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