Bridgestone Hurricane 175 Scrambler
Classic Bikes Bridgestone Hurricane 175 Scrambler | |
Class | Classic |
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Manuals | Service Manual |
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Bridgestone 175 Hurricane Scrambler
Turn a standing quarter in under 17 seconds --
step out and over the bigger guys in the 175+ Dual Twin with Bridgestone's
exclusive dual rotary valve engine -- five-speed, oil injection and dual carbs.
Two-stroke twin engine; dual rotary valves; dual carburetion; oil injection;
bore and stroke, 1.97" x 1.77"; 9.5:1 compression ratio; 20 @ 8000 RPM maximum
horsepower; constant mesh selective 4-speed rotary or 5-speed return change
transmission.
Source as printed in Cycle, © Jan 1967,
reprinted in Walneck's Cycle Trader, Aug 1992
A dual rotary-valve engine, 5-speed
transmission, modern and well-mannered suspension, and a fine finish may not be
everything -- but they're close.
Bridgestone's 175 Hurricane Scrambler is a
logical development of the 175cc "Dual Twin" touring machine the company
introduced a couple of years ago. More and more, motorcyclists look to the woods
for riding fun, and for safety from the the hordes of automobiles that clutter
the nation's highways. Today's motorcyclist, in many if not the majority of
instances, wants a bike he can use either on pavement or out on little-used
trails. It need not be a full-fledged scrambler; that would make the bike
impractical for street riding. The basic requirement is for a highway machine,
with modificatios to give it added power, etc. And that is a pretty good capsule
description of the Bridgestone Hurricane Scrambler.
In the "scrambler," as was and is true of the
pure touring Bridgestone 175, the engine is the most interesting feature. This
engine, which is packed with little items that should delight the technically
inclined, was the first mass-produced two-stroke "twin" to have rotary-disc
inlet valves. Most such engines have nothing more elaborate than a hole in the
back of each cylinder. When the piston skirt's lower edge comes up and clears
the hole, the mixture is drawn into the crankcase. Similarly, the piston skirt
closes the port when it comes back down. A great system from the standpoint of
simplicity, but not without its drawbacks. For one thing, there is a tendency
for the charge drawn into the engine to escape again as the piston moves back
down. This can be countered, to a very large extent, by adjusting the size and
timing of the intake port. But it can only be adjusted to work well over a
limited range.
A disc-type rotary valve is much less
handicapped. By using this device, an engine designer can get any opening and
closing points needed for the intake period. As a result, the power range will
always be a bit wider, for any given level of output, when rotary valves are
used. You may not care about the technical ins and outs of the matter, but you
will care about the engine's wide-range pulling power.
Another point that will, sooner or later, be of
some importance to the buyer is that the Bridgestone engine comes apart and goes
back together in rapid, zip-zip fashion. The mechanic, down at your local
dealer's shop, can do even a total overhaul very quickly, and the labor charges
account for a large part of such repair bills.
There are reasons, too, why the frequency of
repairs should be low. The Bridgestone engine, like most modern two-strokes, has
its crankshaft running in ball bearings, with caged rollers at the
connecting-rod big-ends. Up at the piston-pin ends of the connecting rods, there
are caged needle-roller bearings, and we consider this important. Piston-pin
bearings, in two-stroke engines, are rather poorly lubricated. To make matters
even worse, they are subjected to high temperatures. The plain bushings once
universally used, and still found in some engines, do not like the combination
of heat and scanty lubrication. They wear rapidly, and when worn they clatter
and cause a lot of internal unpleasantness. Needle-rollers, like those in the
Bridgestone, do a lot for reliability.
General over-heating and an occasional piston
seizure has also, in the past, been something of a problem with high-output
two-stroke engines. There are various ways in which designers have overcome such
problems. Bridgestone uses a very direct method. Aluminum is a material that
transfers heat (as from a cylinder to air) particularly well, so they have
simply made the entire cylinder out of aluminum. As in the case of the rotary
valves, all-aluminum cylinders with hard-chrome plated bores had been developed
in racing; Bridgestone was the first to apply this to a touring motorcycle.
These cylinders "cool" very efficiently, and as they expand at the same rate as
the aluminum pistons, seizures will not occur unless something is dreadfully
wrong.
Like most modern two-strokes, the Bridgestone
engine is fitted with an automatic oiling system. A small variable-delivery
pump, engine driven, injects oil into theintake air-stream just behind the
carburetor. This keeps the intake valave disc and its chamber well lubricated,
and the oil manages somehow to find its way around to the various bearings. It
all seems a trifle haphazard, compared to piping the oil directly to the
bearings, but it works about as well as the traditional oil-in-fuel mixtures and
it relieves the owner of the measuring/mixing chore.
Rapid (relatively speaking) ignition
point-breaker wear has always been a problem in two-stroke engines. In most, the
breaker-cam is mounted right at the end of the crankshaft, and turns at
crankshaft speed. Thu, the rubbing speed between cam and fiber point-block is
high, and that accelerates wear. The Bridgestone engine, however, has a separate
gear-driven generator, with the point cam down at the end of its armature. This
is driven at half engine speed, as in a 4-stroke engine, which substantially
reduces point wear. Another benefit is that the ignition system is freed from
the effects of crank flexing at high engine speeds. On many engines, the cam is
right out the end of a long crankshaft extension, and moves around when the
crank flexes. When that occurs, the spark timing wanders somethign shocking.
Bridgestone's remote-mounted ignition was probably forced on them by space
requirements, but this si one of those instances where necessity created virtue.
When the Bridgestone 175 was introduced, it was
especially unusual in having a two-way transmission. With the flip of a lever,
you could have a 4-speed "rotary-shift" transmission, in which neutral was
between 1st and 4th and you could get 1, 2, 3, 4, N, 1, 2, etc. endlessly by
pressing down on the shift lever. Pull the "sportshift" lever, which is mounted
high on the right side of the transmission, over the other way and you had a
5-speed gearbox, with a conventional ratchet change and neutral between 1st and
second. There was another neutral between 4th and 5th, too, and while the first
neutral (the one you wanted) was almost impossible to find, the second unwanted
neutral seemed impossible to avoid. No longer is that the case. A revised
shiting drum gives you the same 4-speed rotary system, but those who use the
5-speed option (which you still get by moving the little lever over) will find
that the pattern is now N, 1, 2, 3, 4, 5. No more problems with finding neutral,
and no more missing the shift between 4th and 5th.
Actually, we cannot think why anyone would want
to use the transmission as a 4-speed unit, but we are told that people do. They
must ride mostly in town. The 5th speed is an overdrive that we cannot imagine
being without when cruising down the highway. Especially with the new Scrambler,
which comes with a 15/38 countershaft/mainshaft combination in place of the
touring model's 16/38. That gives an overall 5th-gear ratio of 6.86:1 for the
street machine and 7.35:1 for the scrambler. The difference in engine rpm at any
given cuising speed is not too great, however, because the Hurricane Scrambler
has a 3.00-18 rear (and front) tire instead of the 2.75-18 rear tire on the
street version.
The "Scrambler's" tires, incidentally, have only
a hint of knobby about them. In fact, the front tire shown in Rockford Motors
(Bridgestone's distributor) ads has a ribbed road-going tread. But the two
examples we had for testing were outfitted with tires, front and rear, having a
fairly coarse block-pattern tread. These do an acceptable job on firm dirt, but
surely aren't much in sand or very loose soil. Still, if a rider uses his head
at all, and doesn't just go plunging ahead into anything, the bike will usually
get from here to there without the benefit of roads.
Out there the really soft slogging is where the
Bridgestone Scrambler lets you know it really isn't a scrambler at all. You get
a healthy 20 bhp from the 177cc engine, but even with the help of the rotary
valves, the power peak is up at 8000 rpm. Worse, the engine's peak torque comes
at 7500 rpm. Both power and torque practically disappear if you let the rev's
fall below 4000 rpm, so the only way you can get through the soft stuff is to
blast along, engine shrieking, and hope for the best. Don't stop for anything;
you may have to carry the bike out on your back.
On the other hand, it must be said that the
Bridgestone Hurricane, unlike some of the "funny-scramblers", is steady enough
under plowed-field conditions to permit blasting-through tactics. The bike's
fork-angle and trail (64" and 3.29", respectively) are more nearly what one
would expect of a scrambler than a street-bike. In a heavyweight motorcycle,
this would result in rather slow, heavy handling. It merely lends added
stability to a lightweight like the Bridgestone, on or off the road. Given a set
of tires better suited to rough-ground conditions, the Bridgestone Hurricane
would be very convincing as a scrambler. But of course that would reduce its
effectiveness as a dual-purpose motorcycle.
Measures taken to adapt the 175 Dual-Twin to
woods riding do not stop with the tires. The normal, low-level exhaust system
has been replaced with a set of upswept high-pipes and mufflers. The arrangement
on the Scrambler is nicely up away from rocks and stumps, but it is possible to
scorch your shins. Vented guards prevent direct contact with the pipes, or
mufflers, but these only work well in highway cruising. In slow-going, the
guards gather heat from the exhaust faster than it can be passed off into the
air, and they become too warm for comfort. We suppose it is a price one must
pay; sport and comfort are not always compatible.
One of the more important modifications has been
the fitting of a skid-plate under the engine. Nothing is quite so discouraging
as having the sharp end of a big rock banged thorugh a crankcase, and a good,
heavy-steel plate is quite a good guarantee that it will not happen. We do wish
that the rear edge of this plate extended down far enough to prevent snagging of
the center-stand. A couple of times, we were caught halfway across a log, unable
to move forward another inch, because the stand was caught.
You may notice that each of the mufflers has a
"stinger" extension. These were added, so we were informed, because without
them, the oily exhaust coats the rear fender. We might also warn you that
removing these stingers makes the exhaust just a trifle too noisy, so don't take
them off just because you think the bike looks better without them.
There may be times when you will be tempted to
hacksaw-away the brace across the handlebars. These bars are marvelous from the
standpoint of comfort and control, but the brace cuts right across one's line of
vision to the speedometer. To stay "legal" on low speed-limit city streets
requires a lot of peering over and under the brace.
We have nothing but good things to say about the
bike's seat. It is wide and soft enough to be comfortable, and Bridgestone has
very thoughtfully made the upper covering on the Hurricane's seat a non-slip
suede. Consequently, this Bridgestone is a bike that you can control while out
banging around in the bushes; you don't have to hang on for dear life at the
same time.
Good things can likewise be said of the bike's
suspension system. It is a fine balance of springing and damping; soft enough to
be comfortable while cruising down the road, yet damped so that there is little
"bottoming" when riding hard in the rough. Indeed, the only time we were able to
make the suspension hit the limit of travel was in jumping the bike -- and there
are few that do not present you with a clank or two under such treatment.
And if you ride much where the air is especially
dusty, the Bridgestone's fine air-filtration system will save its engine from an
early grave. Each carburetor is housed in a sealed chamber, and the chamber is
connected (via a large-diameter tube) to a canister behind the engine containing
a big, fiber-type filter element that will stop any air-borne particle large
enough to damage the engine's internals.
Like all the Bridgestone motorycles we have seen,
the finish on this 175 Hurricane is exceptionally good. Not in the sense that
anything is hand-fitted; this bike is the result of careful mass-production
techniques, and doesn't need "old-world craftsmanship." Everything fits,
and works properly. You know it form the solid feel of the machine, and the way
controls operate. Especially, you get a feeling of confidence form the way the
rev's climb, climb, climb. And from the smooth, positive gear-change. After a
few thousand miles, it may all take a change for the worse, of course, but we
don't think it will. The Bridgestone is just too nice to flatter only to
deceive. We like it; you will too.
Source as printed in Cycle, © Jan 1967,
reprinted in Walneck's Cycle Trader, Aug 1992