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.”
Thoroughly up to date, the Yamaha TX750 wore a single front disc, with provision for a second already built into the left fork leg. Starting was electric, and shifting was courtesy of a five-speed borrowed from its smaller brother, the newly-named Yamaha TX650. The blocky, almost chiseled-looking overhead-cam engine was all new, with a unique cast-aluminum exhaust manifold that doubled as a balance tube, further smoothing out the pulses from the counter-balanced twin.
If this wasn’t enough to get the Yamaha TX750 some ink, a controversial trio of lights housed between the bike’s speedo and tach, a “diagnostic panel,” made sure the new model was noticed. Oil pressure warning lights were nothing new, but Yamaha upped the ante by including not only an oil light, but also a rear brake lining warning light and a rear brake light warning lamp.
The brake lining warning light would set when lining thickness dropped to 2mm or less. But the brake light warning lamp came on whenever the brakes were activated. If the rear brake light burned out, the warning lamp would flicker madly every time the brakes were hit. If the rear tail lamp burned out the brake light would light, but dimmer than normal, and the warning light would stay on.
While some riders saw this as a positive move toward onboard diagnostics, more thought the system was just plain stupid. “It does strike us that a red light that comes on when things are working satisfactorily might be a bit much, especially when the same light flashes when things get out of whack,” Cycle said in its March 1973 issue.
Unfortunately, talk quickly turned sour as TX750s started blowing up crankshafts. Ironically, the problem lay with the very feature that made the bikes special, the Omni-Phase balancer: At high rpm the balance weights would whip oil in the sump into a froth, aerating the oil and starving the crank for lubrication.
Compounding problems, the balance chain tended to stretch, knocking the counterweights out of phase and making the engine rougher than a standard twin. Yamaha quickly devised fixes for all of these problems, including a deeper sump and an adjustable balance chain, but the damage had been done. As quickly as the TX750’s star had risen, it dropped to the ground, the model’s name quickly becoming synonymous with poor design and poor reliability.
The Yamaha TX750 returned for the 1974 model year, changes limited to the afore-mentioned mechanical tweaks and a switch in color from Metal Flake Gold to Burgundy Wine Flake (purple metal flake to most eyes). Sales failed to recover, and the model was quietly round-filed and dropped from Yamaha’s line-up.
The truth is, TX750s are good motorcycles, and can be as reliable as the next machine. Change the oil frequently and avoid high rpm, and you can even get away with the early-style oil sump, which some owners think looks better. Parts are, admittedly, hard to find, but the bike’s classic good looks and solid handling — plus an enthusiastic circle of owners (check out www.tobyfolwick.com/tx750) — makes the Yamaha TX750 an interesting alternative for the rider who thinks less, as in cylinders, is more.
750cc twin alternatives to the Yamaha TX750
1973-1980 Triumph T140V Bonneville
- 50hp @ 7,000rpm/110mph
- Air-cooled, four-stroke parallel twin
- Single disc front and rear (1976)
- 414lb (w/half-full tank)
Introduced in 1959, the Triumph Bonneville was the bike that made Triumph’s fortune in the U.S. The essence of British cool, for years the Bonnie was the bike to beat. By the early Seventies, however, a lack of development meant it was just an old bike in dire need of some new blood: enter the Triumph T140V Bonneville in 1973.
With a 100cc boost in capacity (up from 650cc to 750cc) a new five-speed transmission and a front disc brake, Triumph’s venerable machine looked ready to keep its crown as the king of big-bore parallel twins. No, it still didn’t have an electric starter (that would come much later, in 1980), but its lowered oil-in-frame (first introduced in 1971) gave a better rider stance, and its excellent handling made the Bonneville a favorite among riders who liked their bikes, well, British, thank you very much.
Nobody could mistake the Bonneville for anything but, and even the Japanese admired this most Anglican of bikes, evidenced by Yamaha’s 650cc overhead-cam series, a flattering homage to the Bonneville’s classic lines if ever there was one.
Good examples are easy to find, and an ample parts supply means they’re easy to keep on the road. Reliability can be improved with ignition and carburetion upgrades, and dollars per pound, the T140V is easily one of the best values in classic Triumph motorcycling.
1968-1977 Laverda 750 SF
- 66hp @ 7,300rpm/117mph (1973)
- Air-cooled, four-stroke parallel twin
- Dual disc front, single rear (1974)
- 510lb (wet)
Introduced in the U.S. in 1968 as the American Eagle, the Laverda 750 SF twin was the Italian company’s first foray into the growing big-bore market, and it wanted a hit. To ensure reliability, Laverda opted for Bosch generators and Nippon Denso starters, while the 360-degree parallel twin’s crankshaft ran on five main bearings.
The frame was a massive, ruggedly constructed backbone affair designed to absorb the twin’s vibrations, and while the bike was a bit of a porker weight-wise, it handled better than anything out of Japan. European riders flocked to Laverda’s twin, where it performed well in endurance racing.
A front disc brake came in 1974, followed almost immediately by a dual-disc setup and a rear disc brake. Cast alloy wheels came in 1975, but Laverdisti generally consider the wire-spoked models the best looking of the breed. Increasing competition and the development of Laverda’s own 1000 triple spelled the end of the Laverda 750 SF, and production wound down in 1976, with a few bikes leaving the factory in 1977.
With an estimated 19,000 built, SFs aren’t exactly plentiful. But excellent construction — combined with a committed group of appreciative owners — means there are still plenty of good examples to be found. Parts are easier to find than you’d expect, and thanks to their robust construction a Laverda twin can rack up the miles with ease. MC