JAWA 250 TRIALS-BRIDGESTONE 1754lERCULES 100rhree Watt-The-Road Tests n A Day at the Scrambles Races

A dual rotary-valve engine, 5-speed transmission,modern and well-mannered suspension, and a finefinish may not be everything-but they’re close.

ndgestone’s 175 Hurricane Scram-B’:bler 1s a logical development of the175cc “Dual Twin” touring machine thecompany introduced a couple of yearsago. More and more, motorcyclists lookto the woods for riding fun, and forsafety from the hordes of automobilesthat clutter the nation’s highways. To-day’s motorcyclist, in many if not themajority of instances, wants a bike hecan use either on pavement or out onlittle-used trails. It need not be a full-.fledged scrambler; that would make thebike impractical for street riding. Thebasic requirement is for a highway ma-chine, with modif icat ions to give i t addedground clearance, low-speed pullingpower, etc. And that is a pretty goodcapsule description of the BridgestoneHurricane Scrambler.

In the “scrambler,” as was and is trueof the pure touring Bridgestone 175, theengine is the most interesting feature.This engine, which is packed with littleitems that should delight the technicallyinclined, was the first mass-producedtwo-stroke “twin” to have rotary-discinlet valves. Most such engines havenothing more elaborate than a hole in theback of each cylinder. When the pistonskirt’s lower edge comes up and clearsthe hole, the mixture is drawn into thecrankcase. Similarly, the piston skirtcloses the port when i t comes back down.A great system from the standpoint ofsimpl ic i ty , but not wi thout i t s drawbacks .For one thing, there is a tendency for thecharge drawn into the engine to escapeagain as the piston moves back down.This can be countered, to a very largeextent, by adjusting the size and timingof the intake port. But it can only beadjusted to work well over a limitedrange.

A disc-type rotary valve is much lesshandicapped. By using this device, anengine designer can get any opening andclosing points needed for the intake pe-Cod. As a result, the power range willalways be a bit wider, for any given

level of o”tput, when rotary valves areused. You may not care about the tech-nical ins and outs of the matter, but youwill care about the engine’s wide-rangepulling power.

Another point that will, sooner orlater, be of some importance to the buyeris that the Bridgestone engine comesapart and goes back together in rapid,zip-zip fashion. The mechanic, down atyour local dealer’s shop, can do even atotal overhaul very quickly, and laborcharges account for a large part of suchrepair bills.

There are reasons, too, why the fre-quency of repairs should be low. TheBridgestone engine, like most moderntwo-strokes, has its crankshaft runningin ball bearings, with caged rollers at theconnecting-rod big-ends. Up at the pis-ton-pin ends of the connecting rods,there are caged needle-roller bearings,and we consider this important. Piston-pin bearings, in two-stroke engines, arerather poorly lubricated. To make mat-ters even worse, they are subjected tohigh temperatures. The plain bushingsonce universally used, and still found insome engines, do not like the combina-tion of heat and scanty lubrication. Theywear rapidly, and when worn they clatterand cause a lot of internal unpleasant-ness. Needle-rollers, like those in theBridgestone, do a lot for reliability.

General over-heating and an occa-sional pis ton seizure has also, in the past ,been something of a problem with high-output two-stroke engines. There arevarious ways in which designers haveovercome such problems. Bridgestoneuses a very direct method. Aluminum isa material that transfers heat (as froma cylinder to air) particularly well, sothey have simply made the entire cylin-der out of aluminum. As in the case ofthe rotary valves, all-aluminum cylinderswith hard-chrome plated bores had beendeveloped in racing; Bridgestone was thefirst to apply this to a touring motor-cycle. These cylinders “cool” very ef-

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ficiently, and as they expand at the samerate as the aluminum pistons, seizureswil l not occur unless something is dread-fully wrong.

Like most modern two-strokes, theBridgestone engine is f i t ted with an auto-matic oiling system. A small variable-delivery pump, engine driven, injects oilinto the intake air-stream just behind thecarburetor. This keeps the intake valvedisc and its chamber well lubricated, andthe oil manages somehow to find its wayaround to the various bearings. It allseems a trifle haphazard, compared topiping the oi l direct ly to the bearings, butit works about as well as the traditionaloil-in-fuel mixtures and it relieves theowner of the measuring/mixing chore.

Rapid (relatively speaking) ignitionpoint-breaker wear has always been aproblem in two-stroke engines. In most,the breakersam is mounted right at theend of the crankshaft, and turns at crank-shaft speed. Thus, the rubbing speed.be-tween cam and fiber point-block is high,and that accelerates wear. The Bridge-stone engine, however, has a separategear-driven generator, with the pointcam down at the end of its armature.This is driven at half engine speed, as ina 4-stroke engine, which substantiallyreduces point wear. Another benefit isthat the Ignition system is freed fromthe effects of crank flexing at high en-

gine speeds. On many engines, the camis right out the end of a long crankshaftextension, and mcwes around when thecrank flexes. When that occurs, the sparktiming wanders something shocking.Bridgestone’s remote-mounted ignitionwas probably forced on them by spacerequirements, but this is one of those in-stances where necessity created virtue.

When the Bridgestone 175 was intro-duced, it was especially unusual in hav-ing a two-way transmission. With the f l ipOf a lever, you could have a 4-speed“rotary-shift” transmission, in whichneutral was between 1st and 4th and youcould get 1, 2, 3,4, N, 1, 2, etc. endlesslyby pressing down on the shift lever. Pullthe “sportshift” lever, which is mountedhigh on the s ide of the t ransmission, overthe other way and you had a S-speedgearbox, with a conventional ratchetchange and neutral between 1st and sec-ond. There was another neutral between4th and Sth, too, and while the first neu-tral (the one you wanted) was almostimpossible to f ind, the second unwantedneutral seemed impossible to avoid. Nolonger is that the case. A revised shift-ing drum gives you the same 4-speedrotary system, but those who use the5-speed option (which you still get bymoving the little lever over) will findthat the pattern is now N, 1, 2, 3, 4, 5.No more problems with finding neutral,

and no more missing the shift between4th and 5th .

Actually, we cannot think why anyonewould want to use the transmission as a4.speed unit, but we are told that peopledo. They must ride mostly in town. The5th speed is an overdrive that we cannotimagine being without when cruisingdown the highway. Especially with thenew Scrambler, which comes with a15138 countershaftJmainshaft combina-tion in place of the touring model’s16/38. That gives an overall Sth-gearratio of 6.86~1 for the street machineand 7.35: I for the scrambler. The dif-ference in engine *pm at any given cruis-ing speed is not too great, however, be-cause the Hurricane Scrambler has a3.00-18 rear (and front) tire instead ofthe 2.7518 rear tire on the street ver-s ion .

The “Scrambler’s” tires, incidentally,have only a hint of knobby about them.In fact, the front tire shown in RockfordMotors (Bridgestone’s distributor) adshas a ribbed road-going tread. But thetwo &amples we had for testing wereoutfitted with tires, front and rear, hav-ing a fairly coarse block-pattern tread.These do an acceptable job on firm dirt,but surely aren’t much in sand or veryloose soil. Still, if a rider uses his headat al l , and doesn’t just go plunging aheadinto anything, the bike will usually get

from here to there without the benefitof roads.

Out there the really soft slogging iswhere the Bridgestone Scrambler letsyou know it really isn’t a scrambler atall. YOU get a healthy 20 bhp from thel77cc engine, but even with the help ofthe rotary valves, the power peak is upat 8000 rpm. Worse, the engine’s peaktorque comes at 7500 rpm. Both powerand torque practically disappear if youlet the rev’s fall below 4000 rpm, so theonly way you can get through the softstuff is to blast along, engine shrieking,and hope for the best. Don’t stop foranything; you may have to carry the bikeout on your back.

On the other hand, it must be said thatthe Bridgestone Hurricane, unlike someof the “funny-scramblers” is steadyenough under plowed-field conditions topermit blasting-through tactics. Thebike’s fork-angle and trail (64” and3.29’,, respectively) are more nearlywhat one would expect of a scramblerthan a street-bike. In a heavyweight mo-torcycle, this would result in rather slow,heavy handling. It merely.lends addedstability to a lightweight like the Bridge-stone, on or off the road. Given a set oftires better suited to rough-ground con-ditions, the Bridgestone Hurricane wouldbe very convincing as a scrambler. Butof course that would reduce its effective-ness as a dual-purpose motorcycle.

Measures taken to adapt the 175 Dual-Twin to woods riding do not stop withthe tires. The normal, low-level exhaustsystem has been replaced with a set ofupswept high-pipes and mufflers. Thearrangement on the Scrambler is nicelyup away from rocks and stumps, but itis possible to scorch your shins. Ventedguards prevent direct contact with theexhaust pipes, or mufflers, but these onlywork well in highway cruising. In slow-going, the guards gather heat from theexhaust faster than it can be passed offinto the air, and they become too warmfor comfort. We suppose it is a price onemust pay; sport and comfort are not al-ways compatible.

One of the more important modifica-tions has been the fitting of a skid-plateunder the engine. Nothing is quite sodiscouraging as having the sharp end ofa big rock hanged through a crankcase,and a good, heavy-steel plate is quite agood guarantee that it will not happen.We do wish that the rear edge of thisplate extended down far enough to pre-vent snagging of the center-stand. Acouple of times, we were caught half-way across a log, unable to move for-ward another inch. because the stand wascaught.

You may notice that each of the muf-flers has a “stinger” extension. Thesewere added, so we were informed, be-

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cause without them, the oily exhaustcoats the rear fender. We might alsowarn you that removing these stingersmakes the exhaust just a trifle too noisy,so don’t take them off just because youthink the bike looks better without them.

There may be times when you will betempted to hacksaw-away the braceacross the handlebars. These bars aremarvelous from the standpoint of com-fort and control, but the brace cuts rightacross one’s line of vision to the speed-ometer. To stay “legal” on low speed-limit city streets requires a lot of peeringover and under the brace.

We have nothing but good things tosay about the bike’s seat. It is wide andsoft enough to be comfortable, andBridgestone has very thoughtfully madethe upper covering on the Hurricane’sseat a non-sl ip suede. Consequently, thisBridgestone is a bike tHat you can con-

trol while out banging around in thebushes; you don’t have to hang-on fordear life at the same time.

Good things can likewise be said ofthe bike’s suspension system. It is a finebalance of springing and damping; softenough to be comfortable while cruisingdown the road, yet damped so that thereis little “bottoming” when riding hard inthe rough. Indeed, the only time we wereable to make the suspension hit the limitof travel was in jumping the bike-andthere are few that do not present youwith a clank or two under such treat-ment .

And if you ride much where the air isespecially dusty, the Bridgestone’s fineair-filtration system will save its enginefrom an early grave. Each carburetor ishoused in a sealed chamber, and thechamber is connected (via a large-diam-eter tube) to a canister behind the en-

gine containing a big, fiber-type filterelement that will stop any air-borne par-ticle large enough to damage the en-gine’s internals .

Like all the Bridgestone motorcycleswe have seen, the finish on this 175 Hur-ricane is exceptionally good. Not in thesense that anything is hand-fitted; thisbike is the result of careful mass-produc-tion techniques, and doesn’t need “old-world craftsmanship.” Everything fits,and works properly. You know it fromthe solid feel of the machine, and theway controls operate. Especially, you geta feeling of confidence from the way therev’s climb, climb, climb. And from thesmooth, positive gear-change. After afew thousand miles, it may all take achange for the worse, of course, but wedon’t think it will. The Bridgestone isjust too nice to flatter only to deceive.We like it; you will too. 0

BRIDGESTONE 175 SCRAMBLER

Engine type ......................... .2-stroke twin. rotary valvesDisplacement .................................................... ..... ,177~~Bore & stroke ............ ................ .... ... .50mm x 45mmCompression ratio .... ......... ...................... .. . .. .9.5:1Maximum horsepower .............................. 20 @ 8000 rpmIgnition ...................................................... Battery and coilStarting system .......................................................... K ickElectrical system ....... .......... .. ................... AlternatorClutch ...... .................. ......... .............. .... Wet multi-discTransmission .. ..6spee d rotary or 5-speed return, footshiftGear ratios.. .... (1) 22.6 (2) 14.4 (3) 10.7 (4) 8.62 (5) 7.35Frame ............................................ Cradle, single downtakeSuspension, front .... ... ........ .............. .... .. TelescopicSuspension. r e a r ............. ... .. .......... .. Swinging armB r a k e s .. ..Twi n leading shoes (front), single leading shoe

(rear), full-widthTires ...... .......... ... 3.00” x 18” (front and rear), full-widthInstrumentation . . . . . . . . . . . . . . . . . . . . . . . Speedometer/odometerWheelbase ............ .. .......... ........ .......................... 48.6”Overal l length ............... .................................... .74,2”Overal l width .......... ....... ....................... .. ... . ..... .26.8”Overall height ............................................................ 40.2”Seat height ............................................................... .31.2”Ground clearance ................ ...................................... .6.3”Weight (dry) ..... ................ .................................. .271 IbsMaximum speed (claimed) .................................. .85 mphPrice ....................... ............................................... $650.00

EVALUATION SUMMARY

Shockdampening .GOODRiding COrn‘Dti .,..,, GOOD

TRANSMlSSlON

BRAKES

3 2 CYCLE