Bridgestone’s disc-valve, 350 GTR two-stroke was a machine way ahead of its time when it hit the streets in ’67
Carving my way through the rushhour traffic on the outskirts of Manchester, I’m becoming increasingly impressed by the bike I’m riding. Partly, that’s because it feels more like a rider’s machine than a show pony. Oh, it’s tidy all right, but it proudly wears the patina of its 50 gloriously unrestored years – and owner Alister Vickers has got it set up perfectly. But it’s also because it’s a very fine motorcycle.
It starts with just a prod on the left-hand kickstart, the brakes work perfectly, the clutch is light and progressive and there’s plenty of zip in the 345cc engine. I’ve never had the pleasure of riding a Bridgestone 350 GTR before, but I’m rapidly coming to the conclusion that that’s what it is – a real pleasure.
Bridgestone weren’t shy about singing the praises of their middleweight twin when it hit the streets in 1967. ‘The most advanced motorcycle ever built,’ trumpeted their American sales literature. The thing is, though, unlike many an advertising claim, this one might just have been true. Let’s look at the specs: six-speed gearbox, a claimed 40bhp, a top speed over the magic ton, twin-leadingshoe front brake and automatic lubrication with pressure feed to the main bearings.
Fair play, Suzuki had all that a year earlier on their 250cc T20, but the GTR throws rotary valve induction into the mix. And there’s a host of top quality detail touches like the built-in cable-oiling nipples, stainless steel front mudguard and a double-sided gearchange shaft that allowed diehards to mount the gearchange on the right – just like on the British bikes that the Bridgestone marketing department hoped they’d abandon in droves. OK, maybe the GTR wasn’t quite the most advanced motorcycle
ever built – but it was certainly very good.
The 350 GTR was certainly Bridgestone’s high water mark as a motorcycle manufacturer, though. The company may be best known for its tyres, but it moved into bicycle production in the aftermath of World War II and then into the clip-on engine market as many of its competitors – including Honda – also did.
From buying in engines initially, Bridgestone steadily improved its two-wheeled offering, producing its first motorcycle – the 50cc Champion – in 1958. The Bridgestone range gradually expanded, getting a major boost by the recruitment of ex-lilac and Tohatsu engineers following the demise of their respective companies. The 1964 BS90 – followed in 1965 by the BS50 and BS175, and in 1967 by the BS350 – was the result.
The entire range used disc-valve engines, which would set the template for Bridgestone motorcycles until production ceased in 1971. That cessation was not a reflection on the excellent motorcycles the firm produced, but rather a result of the growing demands of the thriving tyre production lines, possibly a little commercial pressure from other manufacturers who bought vast quantities of tyres for their own machines, and also the fact that Bridgestone quality didn’t come cheap. In the UK – where Bill Smith Motors were the sole importers – the 350 GTR cost almost as much as a Triumph or BSA 650.
But, if motorcycles had to make way for tyre manufacture, the bikes that Bridgestone produced before calling it a day stand comparison with the best of their rivals. To showcase their engineering prowess, Bridgestone produced an innovative, watercooled 50cc road racer ridden at the Dutch TT by Tommy Robb, Jack Findlay and Isao Morishita in 1966; a 250cc motocross machine that won the Japanese national championships in 1965; and the SR series production racers, aimed at the US dirt track and motocross circuit. But, of the road bikes, the 350 GTR was the pinnacle of Bridgestone’s achievement.
The rotary disc-valve engine is a gem. Using disc valves to control port timing meant the Bridgestone engine developed more torque at lower revs than its piston-ported
contemporaries. The crankshaft is a massive, pressed-up four-bearing job with a labyrinth seal at the centre. A pair of disc valves are mounted on the crankshaft, one on each end, while the brace of Mikuni carburettors clamp to stubs on the valve covers, enclosed in neat cast alloy covers.
To keep the engine acceptably narrow, the alternator is mounted behind the barrels on top of the gearbox. And the innovation didn’t stop there, either. Instead of the more familiar iron liners, Bridgestone pioneered the use of plated chrome barrels – the first time the technology had ever been applied to a road bike. There’s even a dry clutch in there. It’s all clever stuff and the result is that the GTR is one of the fastest and most reliable 350s of its era.
That’s one of the things that attracted current owner Alister to the bike in the first place. “I remember reading a road test in an old magazine from years back,” he recalls. “The tester was amazed at how fast the bike was and I thought: ‘That’s the bike for me’. I love two-strokes anyway and I really like original bikes, so this one ticked both those boxes. Malcolm Anderson from the Kawasaki Triples Club – yes, I’m into those, too – bought it at the Stafford show some years ago. It’s a US import, and as soon as I saw it I said I’d buy it. Malcolm didn’t really like it, so he said I could have it whenever I could raise the cash.
“I finally bought it four years ago. When I got it, it had RD250 indicators bodged on, with a switch clipped to the handlebars. I soon got rid of those. The rest of the bike is totally original and the 3884 miles on the clock are genuine. It’s a really early example – the frame number is from the first week of production. It doesn’t get any better than that for me.”
Alister’s enthusiasm for a bike that must have seemed way ahead of its time is obvious, but I need to see for myself what the future looked like in 1967. ‘Pretty good’ is the short answer. I get the chance to try out that tls brake almost straight away, as a set of traffic lights changes to red on a steep hill. There’s bags of feel at the lever and it’s easily as good as any early disc stopper, despite being the same unit as on the
much lighter Bridgestone 175 twin, while the big single-leading-shoe rear provides plenty of extra stopping power when I need it in a hurry.
There’s no doubt, though, that it’s the unusual-looking engine that gives the GTR its soul. With the slightly boxy cases for the carburettors hung on the side of the crankcases it might not be the most classically beautiful power plant of 1967, but boy does it deliver. There’s unexpected torque at minimal revs that makes pottering round town a pleasure. But crack open the throttle and the GTR leaps forward like a Lurcher after a rabbit.
Although there’s ample low-down urge, from around 4000rpm the GTR really gets a move on. Peak power arrives at 7500rpm according to Bridgestone, but the redline – or more accurately red band, as it lasts for 2000rpm – on the tacho starts at a more conservative 6000rpm, and keeping the revs down to that level still provides plenty of go. Period road tests threw up a variety of top speeds for the GTR, but I’d certainly be surprised if this one wouldn’t top the ton – punching well above its weight for a 350 in 1967.
In a week of unusual gearboxes (I’ve also been riding a Suzuki TC250 and a Kawasaki H2) the six-speed gearbox of the GTR throws another variable at me. From neutral, all the gears are down on the left-foot change. That means that changing down right through the ’box can leave me back in neutral when I’m least expecting it. But I soon get the hang of it – though there’s a slightly puzzling yellow warning light on the speedometer that illuminates to let me know when I’m in fifth gear. Presumably, Bridgestone didn’t want their customers forgetting what a high-tech piece of kit they were riding and that they still had another ratio to go.
If the engine’s power characteristics offer the best of both worlds, so too does the physical size of the bike – for a rider of my stature anyway. All too often, the pleasure of a lively middleweight can be dulled a touch by a cramped riding position and an uncomfortable feeling that I must look faintly ridiculous perched atop a bike that’s a size too small. There’s no chance of that with the GTR.
Perhaps to look more imposing for the ‘bigger is better’ American market – where a mere 350 could be regarded as a toy back in the ’60s – the Bridgestone is reassuringly roomy. The 19in wheels help, of course, but the stiff, twin-downtube frame is fairly tall, too, while a
seat height topping 32in and those high ’bars means taller riders can stretch out a bit. The relatively lofty riding position also gives the bike and its rider more presence when negotiating town traffic and, once out on more open roads, there’s plenty of room to move around. Ideal for traffic-splitting in town or hustling along B-road swervery.
Even the suspension was the subject of careful consideration by the Bridgestone designers. While the forks are conventional enough, with their external springs discreetly concealed by practical rubber gaiters, the conservatively chrome-shrouded rear shocks have been provided with a choice of two top mountings to stiffen or soften the suspension movement by varying the angle of the shocks’ action. And, while the suspension on Alister’s bike may have softened over the years, and I’m subjected to a bit of a jolting on the potholed Cheshire lanes, the GTR never feels like it’s going to step out of line.
Despite the obvious care and attention lavished on practically all aspects of the GTR’S design, there are no unnecessary fripperies. No electric start and no indicators (apparently they were available as an optional extra). There’s not even any branding to spoil the expanse of scalloped chrome side-panels on the slim and stylish fuel tank. Instead, the Bridgestone name is emblazoned boldly along each side of the seat above the rear wheel, while the seat itself is topped with faux-suede panels that grip my jeans securely. Perfect when practicing the 13.7s standing-start quarters Bridgestone publicity material boasted of. The Bridgestone is all about delivering quart performance from a pint-pot package. And it does. It must have been a revelation in 1967.
But while there may be no superfluous gadgetry, that’s not to say the Bridgestone is poorly specified. Quite the opposite, in fact. A rev counter is standard, there’s a friction damper and oil injection, too. There’s even a sight glass to see how much two-stroke oil is left in the tank. And the build quality is ahead of any of its rivals from the day.
In fact, this is a bike that’s still a more than capable tool in today’s traffic conditions. Fast enough, stops well, steers well – and looks good, too. It’s hard to believe it’s 50 years old. Sadly, you don’t see too many Bridgestone 350 GTRS on the road, but if you get the chance to beg a ride on one, grab it. I guarantee you’ll be mightily impressed. Back in 1967 the GTR must have seemed like a vision of the future. You could certainly give riders on a 650 Brit twin a fright on the Yamaha LC’S spiritual grandad. It really is that good.
ABOVE: Engine is surprisingly torquey low down, and really gets a move on as the revs rise LEFT: Lighting this up is a satisfying experience. The brakes are good
Automatic lubrication with pressure feed to main bearings was one of the hightech features
Disc valves and carbs live under these alloy covers