Bridgestone Gtr 350
BRIDGESTONE GTR 350
THE THREE-FIFTY CLASS MOTORCYCLE, traditional stepchild of the sport, continues its gain in stature with the unveiling of the new 21-inch Bridgestone. Until recently, the expression "three-fifty" provoked such images as the Junior TT, or a "fun" class in AMA Sportsman scrambles, or a military courier's mount, or an essential element to an ISDT team. Whatever the point of identification, the threefifties are invariably relegated to a position connoting compromise, because while they have always looked like the "real article" — the 500s from which they were typically derived — they have been handicapped by their "sleeved down" cylinders and "destroked" crankshafts. But then the picture changed not long ago. and we suddenly found ourselves confronted with a three-fifty that was promoted from a two-fifty rather than demoted from a five-hundred, and this novel approach proved startling; a twenty-one-inch motorcycle, scaled through the proper end of the telescope, could be an exciting piece of equipment. Hot on the heels of the first new-look twenty-one came number two, and still the freshly drawn set of design-game rules held true; this was, after all, the correct approach.
And now, entry number three in the resurrected displacement category — the Bridgestone 350 dual rotary valve twin, combining sophisticated design, unqualified performance, big bike feel and styling, and craftsmanship with nostalgic internal dimensions.
That the three-fifty class is becoming a major market and the pressure is on is amply illustrated by Bridgestone's 350, because they were not permitted the luxury of a simple transition from a two-fifty like their competitors, yet were forced to make a great giant step all the way from their largest model, a 175cc, to the new big one. And over the long pull that giant step may very well prove to Bridgestone's benefit, because the all-new engine appears to have comfortable growing room — perhaps to well within striking distance of the limit of the 500cc class. In one sense, all-new could be considered a misnomer; design similarities of the 350 and 175 are so numerous that a distinct family resemblance emerges. In the execution of the design, however, the 350 is most certainly all-new, for few of the 175's parts have found their way to this design.
Bridgestone makers are old hands at building rotaryvalve two-stroke twins, having been the first company to mass produce the arrangement, and the 350 reflects their conversance with the concept. One of the chief problems confronting rotary-valve engine designers — that of engine width dictated by location of the carburetors — has been handled very well on the 350, and while the overall width at the carburetor covers is an ample 18 inches, the width of the engine package between the foot pegs has been held to a very trim 14 inches. The location of the carburetors gives rise to yet another problem — placement of ignition and generator. Here again, the solution is a good one with the ignition/generator unit mounted atop the engine cases, aft of the cylinders. And because a clean, cylindrical generator is a more pleasing design element than a cobby carburetor, the 350 experiences a fortuitous improvement in its appearance.
CYCLE WORLD ROAD TEST
Still another problem with rotary-valve design — lubrication of the disc itself — is solved handily in the normal course of supplying injected oil to the engine's internals. Oil from the injection pump, with its output regulated in accordance with engine demand by a secondary cable siamesed to the throttle cable, is fed directly to the outer ball bearing mains, where a small portion of it exits outboard to the rotary valve cavity to lubricate the disc. The remainder of the oil passes through the outer main, where it is picked up by slingers which transfer it to the hollow crankpins. From the crankpins the oil passes through the needle big-end bearings into the crank chamber, where it mixes with the turbulent incoming fuel/air charge to provide mist lubrication of the needle little-end bearing, the chrome-plated aluminum cylinder walls and the roller center mains.
The 350's six-speed transmission is a respectable piece of hardware with several welcome features and one curious one. The transmission mainshaft is carried in ball bearings at either end, and the layshaft uses a ball at the output end and a needle assembly at the "dead end." In addition, conventional needles are used throughout the rest of the unit, and a staggered needle assembly is employed for the idler of the seven-plate dry clutch. The clutch throwout mechanism is lubricated through an external grease nipple. The gear change mechanism, with the selector shaft protruding through both sides of the transmission so that the lever can be swapped from one side to the other, has neutral at the top with all shifts down. Probably because of the 35CTs size and performance, and its consequent appeal to the experienced old hand, Bridgestone did not design a rotarychange mechanism for it.
For reasons best known to the chap who designed the device, there is a fifth-gear indicator light, inspired perhaps by those rolls of disposable sandwich bags which include a small red tag, four bags from the end, warning one that he is about to run out. If an indicator light is felt to be essential, we would opt for one corresponding to sixth gear.
Most assuredly, Bridgestone have some good ideas for frame design in their double-cradle item for the 350. That major chassis joint, the swing-arm pivot, has apparently been given a great deal of thought and thus comes off with an excellent four-point mount. The outer ends of the swing-arm are supported by the cradle loops, and the center of the arm pivot intersects the base of the heavyduty spine tube. A secondary cross member between the arms, several inches behind the pivot, aids the four-point mount in keeping the rear end tracking true. The overall effectiveness of these details, and of the frame in general is clearly illustrated when the bike is pressed hard on uneven road surface: the 350 tracks faultlessly and is free from flexing.
The Bridgestone's front suspension does much to enhance the ride and handling characteristics of the chassis, in that it has long travel, good rebound damping and spring weight that is ideally suited to this truly full-size motorcycle and a full-size rider. The rear suspension, despite the tops of the spring-shocks being mounted in the softer forward position, is good, and like the front, well suited to the motorcycle. The load adjustment feature of the rear legs, while involving considerably more work than multi-position units, seems a better approach to the problem of compensating for load increases in that it doesn't compress the springs, thereby reducing travel, but instead treats the suspension to a better mechanical advantage, and at the same time, retains full travel.
In keeping with a motorcycle with the performance and handling of the 350, the brakes are excellent and will easily match the demands of high-speed touring and windy-road ear-holing. As Japanese as "Ah, so," the brakes consist of a generously dimensioned double-leading-shoe unit in front and an equally generous single-leading-shoe unit in back. They are consistently smooth, quiet and responsive.
The electrical system of the 350 consists of a straightforward AC generator with battery ignition. It incorporates an overcharge relay instead of a demand regulator, and because the peak of primary AC-output is phased with point break, ignition power is independent of battery current level. All of the lighting components and the horn have been given the seal of approval by the California Highway Patrol, whose standards are as high as any in the country.
The styling of the Bridgestone 350 is certainly not going to hurt sales for this new model. We consider it to be one of the handsomest roadsters in all of motorcycling, with a superbly successful blending of Japanese smoothness and English cobbiness. Further, it's, as we've said before, a full-size motorcycle, as big and as fast as any five-hundred — and considerably faster than most. The seating and control layout are exceptionally comfortable for the average or larger rider.
Overall finish and workmanship are quite good. Frame welding, in spots, is rough, but this is offset by excellent plating, the nicely detailed — and beautifully styled — seat and the incredible casting finish on the barrels and heads. The Bridgestone's instrumentation seems to have received the type of attention that characterizes the major components of the machine, because the tack and speedo are easily read, rubber mounted, have offset drives to facilitate comfortable cable routing and they're as good looking as any we've seen.
At the time we performance tested the GTR, it had already been subjected to a great deal of hard running, but such is its fate, for the test bike is the first production unit to be sent to the U.S. and it's being used as a sort of. "proof" machine to ensure that the thousands of hours of development time that have preceded its construction have uncovered all potential weaknesses and flaws. Possibly the most rigorous phase of Stateside testing involved more than 80 standing-start 14-mile acceleration runs within a three-hour period.
We are told that the best runs of this series netted ETs of less than 15 seconds. The test series, unfortunately but understandably, was the ruination of the cylinder bores. A set of replacement cylinders were hurriedly airfreighted from Japan, but, unhappily, were an early prototype set that were not up to the standards of the production units. In short, they would not permit the motorcycle to realize its full performance potential, and thus it is that the only valid performance figures obtained on the GTR in this country were those garnered during Rockford's testing of the bike with the original production cylinders.
There's scarce reason to doubt that Bridgestone will be making their mark on the big bike market with their 350. The motorcycle's range of appeal is broad, offering something for the technically oriented mind, the styleconscious set, the class racer, and even the gent who wants nothing more than comfortable, dependable high-speed touring at a reasonable price.
BRIDGESTONE
350 GTR
$850
SPECIFICATIONS
