Bridgestone 350 GTR
Added on Wednesday, May 9th, 2012 by Carole Nash Editor | No Comments
Bridgestone 350 GTR
The GTR was one of the most sophisticated bikes of its day, yet not long after this bike left the factory in 1967, Bridgestone not only ceased production of the GTR but gave up making motorbikes altogether. Roland Brown discovers why…
Accelerating out of a curve with the little two-stroke twin revving eagerly, sun gleaming off its chromed petrol tank and a high-pitched exhaust note providing a vivid soundtrack, it was easy to understand why Bridgestone’s 350 GTR was widely regarded as one of the best Sixties middleweights. And it was sad to think that this model was the high point for a firm that abandoned motorcycle production shortly after it was built.
The GTR was one of the most sophisticated bikes of its day, featuring a disc-valve induction parallel twin engine as well as a generally high quality of construction. Decades after it was built, this immaculate GTR impresses with its neat looks, crisp performance and reliable handling. Yet not long after this bike left the factory in 1967, Bridgestone not only ceased production of the GTR but gave up making motorbikes altogether, to concentrate on the tyres for which the Japanese company is still well known.
After riding the twin, that decision seems strange, although it makes more sense when you realise that in 1968 the GTR cost more than BSA’s Thunderbolt 650 parallel twin and only £30 less than a Triumph Bonneville. The GTR was good alright, but in most people’s minds it wasn’t that good. Many motorcyclists were unconvinced about the appeal of the relatively little-known Japanese company and its flagship two-stroke twin, with the result that only small numbers of GTRs were sold in the USA and even fewer in Europe before production ended in 1969.
The most notable aspect of the 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 then used by rival two-stroke roadsters. Bridgestone’s twin used a disc valve (one for each cylinder) on each end of its crankshaft, with a 26mm Mikuni carburettor bolted outside each valve. Another neat feature was the ‘piggy-back’ alternator, situated above the engine rather than at the end of the crankshaft, which allowed the GTR unit to be quite slim despite its side-mounted carbs. Peak output was normally claimed to be 37bhp at 7500rpm, although the figure of 40bhp was also quoted in places.
The GTR’s advanced engine features did not end with its induction. Lubrication was by a Yamaha-style pump-operated system, to which the Bridgestone added the refinement of inspection windows for both engine and gearbox oil. Similarly the GTR impressed with its six-speed gearbox, and with its facility to swap the gearlever and rear brake pedals to give a left- or right-foot gearchange, both of which were commonly used at the time. But the Bridgestone also annoyed because its neutral was placed at the top of the six-speed gearbox, instead of between first and second as on most bikes.
The rest of the GTR was relatively conventional. Its twin-downtube steel frame, gaitered front forks, chromed twin shocks, and 19-inch wheels with drum brakes front and rear were very much standard fare when the GTR was first sold on the American market in 1966. Visually it was similar to its 90cc and 175cc siblings, and there were also models with off-road styling, notably the 350 GTO which was built in even smaller numbers than the GTR.
Few Bridgestones can have survived in better condition than this 1967-model GTR, which was originally sold in the USA, and was restored by Wiltshire-based marque enthusiast and collector Brian McDonough after arriving in Britain. The bike looked superb and felt light, slim and quite tall as I stood alongside it, and fired the two-stroke motor into life with a gentle swing on the kickstarter.
Back in the late Sixties, the Bridgestone’s revvy motor and light weight of just 161kg made the two-stroke a match for almost an bike away from the line, which boosted its popularity in America. Bridgestone quoted a standing quarter-mile time of 13.7 seconds. Even though it wasn’t really as quick as that, the GTR provided plenty of acceleration away from the lights — and if the front wheel did come up occasionally to produce that Sixties rarity of a wheelie, I can’t imagine many wide-eyed owners would have complained.
Inevitably the upright riding position dictated by the Bridgestone’s fairly high and wide handlebars would have made high-speed riding tiring, though this was hardly a criticism in the days when fairings were rarely fitted as accessories, let along as standard. On my ride the bike was comfortable enough, thanks to a reasonably well padded seat, plus suspension that was reasonably firm without being too stiff.
Handling was good by contemporary standards, thanks also to a twin-cradle steel frame that was rigid enough to prevent the notorious head-shaking suffered by some rival two-strokes. Neither the forks nor the shock units had any adjustment, even for preload, but the shocks could be tuned by moving the top mounts, with the ride getting firmer with the units set vertically. This bike’s angled-forward units weren’t too far out for my 85kg.
Similarly, the GTR’s drum brakes worked quite well, with even the twin-leading-shoe front unit that was borrowed from the firm’s 175cc model providing reasonable stopping power. I also had no problem with the 350’s tyres, which predictably enough were Bridgestones, and gripped well despite their narrow size (though it would probably have been a different story in the wet).
Unfortunately for Bridgestone, the GTR’s quality came at a high price, for the bike cost considerably more than rival Japanese two-strokes, and was competing directly with larger engined four-strokes. It also faced resistance from riders who were dubious about a high-performance two-stroke’s reliability. This concern was not unreasonable, given the problems that early motors had with oil seals, and with broken air filter parts being sucked into the engine.
Relatively small numbers were sold in the States, following the model’s introduction there in 1966. Towards the end of the following year the GTR went on sale in Britain, but only a few dozen were sold here. By 1968, Bridgestone was coming under pressure from rival Japanese marques which were also customers for its tyres, the company’s most important product. (Bikes were only ever a sideline.) Shortly afterwards, Bridgestone quit bike manufacture to concentrate on tyres.
|Bridgestone 350 GTR (1967)|
|Engine type||Aircooled two-stroke parallel twin|
|Bore x stroke||61 x 59mm|
|Carburation||2 x 26mm Mikuni|
|Claimed power||37bhp @ 7500rpm (or 40bhp)|
|Transmission||6-speed, dry clutch|
|Electrics||12V battery, coil ignition|
|Frame||Tubular steel duplex cradle|
|Front suspension||Telescopic, no adjustment|
|Rear suspension||Twin shock absorbers, adjustment via alternative top mountings|
|Front brake||178mm tls drum|
|Rear brake||178mm sls drum|
|Front tyre||3.00 x 19in (Bridgestone Mag Mopus)|
|Rear tyre||3.50 x 19in (Bridgestone Mag Mopus)|
|Fuel capacity||15 litres|