The Yamaha TX750
What’s best — two, three or four cylinders?
The Yamaha TX750.
Years produced: 1973-1974
Claimed power: 63hp @ 7,500rpm
Top speed: 105mph (period test)
Engine type: 743cc single-overhead cam, air-cooled parallel twin
Weight (wet): 235kg (518lb)
Price then: $1,554 (1973)
Price now: $1,200-$2,800
What’s best — two, three or four cylinders? That's what the marketing boys wanted to know as demand for big-bore bikes was building in the early Seventies. Honda and Kawasaki were betting on fours (the Honda CB750 Four and Kawasaki Z1, respectively), but neither Suzuki nor Yamaha, the other half of Japan’s Big Four, had signaled a clear direction.
Suzuki engineers were feverishly developing what they thought would be the Next Big Thing, the ill-fated Suzuki RE5 rotary, as the future seemed to point to new designs or more cylinders. That made Yamaha’s 1972 announcement of the 750cc Yamaha TX750 parallel twin, a classic engine configuration if ever there was one, more than a little surprising.
Two versus four
Four-cylinder engines appeal in large part thanks to their smoothness. But Yamaha figured they were bigger, heavier, more complicated, and more expensive to build and own. So Yamaha turned to the venerable parallel twin, a configuration that had served them well in everything from little two-strokers to the successful 650cc overhead cam Yamaha XS-1 announced in 1969.
The downside of the classic parallel twin was, of course, vibration: Regardless of how you phase the crank, a two-cylinder engine’s going to jump every time those big cylinders rise and fall. Yamaha decided to counter this — and give new life to an old design — with what it called the Omni-Phase balancer.
Using a pair of balancers (one clocked to counter the primary imbalances of the cylinders, the other to counter the rocking coupling created by the first balancer), Yamaha’s Omni-Phase all but eliminated vibration in the Yamaha TX750, giving their big-bore twin the kind of smoothness previously thought possible only in a four. Moto journalists loved it: “The result is smoothness beyond belief,” Cycle World said in its October 1972 issue. “Shut your eyes and you are on a four. It couldn’t be a twin.”
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