1967 Bridgestone 350 GTR

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Bridgestone 350 GTR
Years produced: 1967-1971
Total production: 9,000 (est.)
Claimed power: 37hp @ 7,500rpm
Top speed: 95mph
Engine type: 345cc two-stroke, air-cooled parallel twin
Weight (dry): 160.6kg (354lb)
Price then: $695 (1970)
Price now: $1,800-$4,000
MPG: 45 (est.)

Accelerating out of a curve with the two-stroke engine revving hard, sun gleaming off the chromed tank and a high-pitched exhaust note providing a vivid soundtrack, it’s easy to understand why the 1967 Bridgestone 350 GTR was widely regarded as one of the best Sixties middleweights around. It’s also a bit sad to think that this model was the high point for a firm that abandoned motorcycle production shortly after it was built.

The Bridgestone 350 GTR was one of the most sophisticated Japanese motorcycles of the Sixties, featuring a disc-valve induction parallel twin engine as well as generally high quality construction. Almost three decades after it was built, this immaculate GTR impresses with its neat looks, crisp performance and reliable handling. Yet only a few years after this bike rolled out of the factory in 1967, Bridgestone not only ceased production of the GTR but gave up making motorcycles altogether to concentrate on the Bridgestone tires for which the Japanese company is still well known.

After riding the twin, that decision seems strange, although it makes more sense when you realize that the little two-stroke was expensive, costing as much as a Triumph Bonneville in some markets. The GTR was good all right, but in most people’s minds it wasn’t that good. Most motorcyclists were unconvinced about the appeal of the relatively little-known Japanese company and its flagship two-stroke twin, with the result that relatively small numbers of GTRs were sold before production ended in 1971.

Induction production
The most notable aspect of the 350 GTR’s 345cc parallel twin engine was its rotary disc-valve induction system, which allowed much more precise control of gasses than the more simple piston-ported design being used by rival two-stroke roadsters. Ironically, Bridgestone’s Japanese rival Suzuki had considerable experience racing disc-valve two-strokes, but the firm’s 250cc Super Six roadster, also a two-stroke twin, was piston-ported. Suzuki’s experience dated back to 1961, when MZ factory racer and engineer Ernst Degner defected from East Germany, bringing his team’s secrets with him and passing them on.

Bridgestone’s twin used a disc valve (one for each cylinder) on each end of its crankshaft, with a 26mm Mikuni carburetor bolted outside each valve. Another neat feature was the “piggy-back” alternator, situated above the engine rather than at the end of the crankshaft, making the GTR unit quite slim despite its side-mounted carbs. Peak output was normally claimed to be 37hp at 7,500rpm, although a figure of 40hp was also quoted in some materials. (Most manufacturers were optimistic with power and speed claims, and Bridgestone played that game enthusiastically.)