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The
revolution continues: Introducing the Honda 2007 CRF150R and CRF150R-Expert Anybody
with even a passing interest in motocross and Supercross racing recognizes
that a revolution has recently taken place. Within a few short years
four-stroke machines supplanted two-stroke bikes almost completely
throughout the ranks of professional racing, and Honda has played a major
role in this transformation. Since the debut of the CRF450R during the
2002 season, the buying public has purchased well over 100,000 motorcycles
spread between the CRF450R, CRF450X, CRF250R and CRF250X, which makes
Honda's four-stroke Unicam® engine format a runaway best-seller. In
2007 the revolution continues with the introduction of the CRF150R, a
machine destined to transform another segment of the motocross market in a
shift from two-stroke to four-stroke—with all the stellar attributes
that have been quickly proven in Honda's big-bike ranks. In keeping with
the trend begun by the CRF450R and continued with the CRF250R, Honda's new
CRF150R and big-wheel CRF150R-Expert are destined to shake up the
small-displacement classes of two-stroke MX machines. And if the new
little CRF150R looks strangely familiar, it's for good reason: Check out
the engine—it's a scaled-down and updated miniature version of the tried
and proven big CRF Unicam engines. Think
of it as an exercise in modern-day miniaturization, analogous to the
ongoing trend in computer design where evermore-powerful units are
shoehorned into ever-shrinking packages. As
such, the 149cc CRF150R follows almost every key design element common to
both of the larger Unicam four-valve, single-overhead-cam powerplants. A
single chain-driven camshaft directly actuates a pair of intake valves, in
this case measuring 26.0mm. However, instead of employing a forked roller
rocker arm to actuate the two 22.5mm exhaust valves, the CRF150R
incorporates two separate low-friction roller rocker arms. This
arrangement makes it easier to change valve-lash shims when adjusting the
valves, and it also allowed the spark plug tube to be situated between the
two rocker arms to create a very compact cylinder head layout with the
spark plug centrally located in the combustion chamber for optimum flame
propagation. Like its larger CRF siblings, the CRF150R's Unicam layout
produces a very flat 21.5-degree included valve angle that also opens up
the combustion chamber for efficient burning. Because they are lighter and
smaller, all four valves can be made of tough, durable steel, and single
valve springs are used all around. Also in keeping with established Unicam
practice, the CRF150R incorporates a small, lightweight automatic
decompression mechanism that opens the left-side exhaust valve slightly to
make starting a snap. In
keeping with the Unicam practice and race-engine design in general, the
bore and stroke are radically oversquare: 66.0mm x 43.7mm, standing in
stark contrast to the dimensions of the recreationally oriented two-valve
CRF150F, which displaces its 149cc by way of a nearly square bore and
stroke of 57.3mm x 57.8mm. Likewise, the CRF150R's slipper-type
racing-style two-ring piston slides through a Nikasil-lined cylinder to
generate a compression ratio of
11.7:1, which stands much higher compared to the CRF150F's 9.5:1
ratio. The crankshaft is made of high-strength, low-carbon steel with
carburized main journals for optimal durability at sustained high-rpm
operation. In addition, this engine follows Unicam engine design in its
use of two separate oil chambers, one for the engine and one for the
gearbox. This design is instrumental in reducing weight and creating less
oil drag around the crankshaft, as well as lowering the heat load in the
clutch. If
that little carburetor looks familiar, albeit smaller, you've got a good
eye; this FCR type, flat-slide 32mm unit with a throttle position sensor
is a mini-sized version developed specifically for this machine; the
CR85R, in contrast, uses a 28mm flat-slide. And because this is a
larger-displacement engine compared to the CR85R, the CRF150R features
dual radiators in place of the single cooler mounted aboard the
two-stroke. Speaking
of the CR85R, that race-proven platform formed the basis for the CRF150R
rolling chassis, from the tough but light high-tensile steel frame to the
trick aluminum swingarm, fully adjustable 37mm inverted Showa cartridge
fork and Pro-Link rear suspension system with fully adjustable Showa
shock. As would be expected, the CRF150R incorporates its own specific
spring and damping rates. Also, the CRF150R features a smaller and lighter
rear brake system like those found on the big CRF racers, and new,
stronger wheels also sport lighter hubs for less unsprung weight. In
keeping with prior Honda small-displacement motocrosser practice, the
CRF150R is available in small-wheel or big-wheel versions to tailor-fit
growing racers. The wheel configurations are identical to those found with
the CR85R and CR85R-Expert: a pairing of 17-inch front and 14-inch rear
wheels, or the larger duo of 19-inch front and 16-inch rear. As with the
CR85R, the larger wheels found on the CRF150R-Expert model raise seat
height and ground clearance about 1.5-inches, while steering rake is also
increased minimally. The front axle is a stout piece measuring 15mm in
diameter, while the rear axle measures a full 17mm across. As
this new motorcycle progressed from the conceptual to the development
stages, Honda R&D called in some teenaged experts in the field. This
sharp-eyed crew was perhaps even more critical than any in-house
engineers; these youngsters have spent years in the crucible of racing,
and their focus is on winning. Period. From
the get-go, no one had any problems starting this 149cc four-stoke engine,
even the less experienced riders and those who had ridden two-strokes
extensively. More to the point, every young tester simply loved the
CRF150R; they found it amazingly fun and fast to ride, and remarkably
confidence inspiring regardless of racing rank. Many comments concerned
the bike's light and maneuverable feel. With a low CG the CRF150R is
highly maneuverable, and turn-in is remarkable light. Others opined that
because it's so rideable, with so much more torque compared to a
two-stroke, it doesn't really feel any heavier than the CR85R. Regardless
of the physics involved, the net outcome is that the CRF150R makes the
rider more confident; like its bigger four-stroke brothers, this bike
offers a decidedly broader powerband while also pumping out lots of muscle
down low and on the top end. This broad-shouldered power delivery makes
the CRF150R notably easier to ride than a two-stroke, especially while
coming out of turns, and coming off jumps. It's simply a better power
delivery, one that is not as explosive as a two-stroke when the two are
tuned to high states for racing use. Speaking of high states of tune, the
CRF150R generates its peak power at 12,500 rpm, and its rev limit is
higher yet at a remarkable 14,300 rpm, which is 1000 rpm higher than the
limit of the CRF250R, making it a real thoroughbred, through and through. Still
and all, the CRF150R doesn't give up anything for all its gains; this bike
is slightly heavier than the CR85R but that was never an issue with the
toughest critics of all, the assembled group of young racers. The proof?
Every single one wanted to take the bike to the track that weekend in
place of their current race bike, including many that were highly modified
models. With
the introduction of the CRF150R, the transformation of the sport of
motocross continues. This is one triple-distilled, pure racing motocross
bike through and through, in keeping with the winning heritage of Honda's
CRF450R and CRF250R. It's not much of a stretch to predict that this new
pocket-rocket four-stroke will immediately become the favorite of the
closed-course crowd. But there may be one hitch. As
the assembled group of young testers was putting the prototype CRF150R
through its paces, more than one parent was looking on with envious eyes.
With the popularity of adult mini racing, it may be necessary to stock
each garage with two CRF150Rs to satisfy dad as well. |
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