Imagine, for a minute, the perfect motocross bike.
Let your mind wander to unfathomable, unrealistic ideas. Draw up a
sketch of the machine on paper, and don’t forget the vivid details.
Odds are you would want to construct a motocross bike with a light,
narrow, compact chassis. Cradled in the frame would be a potent engine
with plentiful horsepower, yet one that was smooth and easy to ride.
Now imagine that this dream can become a reality, because that’s what
the MXA wrecking crew thought last year when we tested Service Honda’s
CR500AF (AF stands for Aluminum Frame). With an old-school CR500
two-stroke engine cradled in a 2008 CRF250 aluminum chassis, test
riders thought they crossed through the pearly gates and had gone to
heaven.
MXA test riders are a fickle bunch. We want what
we can’t have, and when we get what we want, we aren’t satisfied. Case
in point, we yearned for a bike like the Service Honda CR500AF, because
it had all of the attributes of our dream bike. On the short list were
strong power, solid handling, decreased weight and affordable rebuilds.
Truly, the Service Honda bike covered the best of both worlds. Best of
all, it was an easy dream to see to fruition; in one short phone call
our dream became a reality. Anyone can call A.J. Wagonner at Service
Honda and have a dream machine of their own.
When we tested the Service Honda CR500AF, we
enjoyed the raw power of the engine, coupled with the lightened
handling and feel of the CRF250 chassis. However, having plentiful
experience with 500cc two-strokes from before they were put out to
pasture, we knew that the Kawasaki KX500 engine had some significant
benefits over the CR500 powerplant. Amazingly, Service Honda was on the
same page. They felt that the broader powerband of the KX500 engine in
a modern chassis might make the dream even more dreamy.
Enter the KX500AF.
For the last three years, Service Honda has been selling the Kawasaki
version of their highly popular 500cc conversions in a KX450F chassis.
After much deliberation, A.J. Wagonner decided that for 2009 the
revised KX250F chassis and lighter frame would be better suited for the
KX500 engine. How light is the overall package of the KX500AF? It is
roughly six pounds heavier than a stock KX250F and about 15 pounds
lighter than a stock KX450F.
SHOP TALK: WHAT’S IT ALL ABOUT?
Our most pertinent questions for Service Honda
centered around the amount of time it took the technicians to build the
KX500AF. After all, parts off two dissimilar bikes needed to be melded
together in order to complete the project. According to A.J., 40 hours
were spent from concept to completion. Most of the time (roughly 38
hours) was devoted to the chassis, while only a small fraction of the
total time (about two hours) was spent building the engine. While
Service Honda can build a KX500AF relatively quickly, there is still a
30-day waiting period (and initial $1000 deposit) upon ordering.
Service Honda builds five to ten bikes at a time to speed up the
production cycle.
What exactly is needed to make a Service Honda
KX500AF roll out of the workshop? Starting with a 2009 Kawasaki KX250F
chassis, the technicians tear down the bike to the bare frame and begin
fabricating various areas of the frame. The engine cases are
re-drilled, the swingarm spacers are changed, the head stay and head
stay base are fabricated. Obviously the frame cradle has to be reworked
severely. Service Honda cuts half of the cradle out, and the juncture
of the frame under the gas tank is relocated for engine clearance.
Additionally, the “Y” area of the frame is relocated three to four
inches forward in order to clear the exhaust pipe. The same grade of
aluminum alloy is used on the rebuilt section of frame as on the stock
frame to give the KX500AF the stock look.
A.J. made a point of telling us that reworking the
radiators was the most tedious part of building the bike. The radiators
alone take a five hour chunk of time out of the entire process. The
stock KX250F radiators were used because they have a greater surface
area than the stock KX500 radiators. A.J. has the tanks and the hose
barbs reworked. It was interesting to find out that the left side
radiator was flipped over to become the right side radiator. Why? The
KX250F left radiator was too long and didn’t provide enough room for
the FMF-built KX500AF exhaust.
Service Honda tries to use as many stock parts as
possible in an effort to make replacing these parts as easy as ordering
from your local dealer.
TEST RIDE: TRYING TO TAME THE BEAST
The MXA wrecking crew includes a number of seasoned 500cc two-stroke riders (and
we tested with former 500 National Champion Chuck Sun, Yamaha of Troy
and former National rider Phil Alderton, Willy Musgrave and a host of
other MXA test riders) all who cut their teeth years ago riding
the Open bikes. These test riders remember what it felt like to use a
500cc engine to its full advantage. Of course the younger MXA test
riders couldn’t fathom the techniques needed to ride the Kawasaki
KX500AF fast. The whippersnappers have been spoiled by the
new-generation 450cc four-stroke engines.
ON THE TRACK, THE SERVICE HONDA KX500AF ENGINE RIPPED.
IN COMPARISON TO THE HONDA CR500AF THAT WE TESTED LAST YEAR, THE
KAWASAKI ENGINE WAS HANDS DOWN FASTER. OF COURSE THIS DIDN’T COME AS A
SHOCK TO OLDER MXA TEST RIDERS. WHEN THE TWO MOTORCYCLES WERE STILL IN
PRODUCTION, THE KX500 ENGINE TRUMPED THE CR500 POWERPLANT
On the track, the Service Honda KX500AF engine
ripped. In comparison to the Honda CR500AF that we tested last year,
the Kawasaki engine was hands down faster. Of course this didn’t come
as a shock to older MXA test
riders. When the two motorcycles were still in production, the KX500
engine trumped the CR500 powerplant and was preferred by every MXA
tester (they just preferred the CR500 chassis over the KX500 chassis).
To control the power of the KX500, the best technique is a series of
short shifts to keep the engine in the meat of the powerband. The 14/47
gearing combination worked well at maintaining drive, and the FMF
exhaust and silencer were a nice addition to the engine profile.
The million-dollar question is which is better, a
modern KX500 or a modern four-stroke? In a head-to-head comparison, the
500cc two-stroke engine was much more difficult to ride. It came on
harder, pulled harder and required a moment’s thought before pulling
the trigger (and the shortish KX250F chassis didn't help calm it down).
The 450 four-stroke, while no dog, didn’t create the same kind of
hesitancy. With the advent of new technology and a revised approach to
the engine characteristics of four-strokes, the smooth and
rider-friendly four-stroke powerband trumped the 500cc engine (not in
pure speed, but in usability).
In the concept department, the Service Honda
KX500AF seems to be an ingenious idea. Melding the power of a 500cc
two-stroke with the technology of a 250cc four-stroke sounds like a
match made in heaven. The power-to-weight ratio is unheard of among
motocross bikes, but this marriage isn’t perfect.
MXA test riders quickly discovered that the stock
KX250F suspension needs help in order for the KX500AF to corner well
and soak up bumps. We ran 90mm of sag in an attempt to keep the rear
end up in the stroke, and we also turned in the high- and low-speed
compression. These changes helped the front end stick better through
corners, but eventually a stiffer shock spring was required to help
resolve our issues. We also struggled with the front end; there was a
push from center-out in corners. Not surprised by this feeling (the
stock KX250F has the same sensation), we swapped out the 23.5mm offset
triple clamps for a set of 22mm clamps. This change made a solid
improvement in the turning ability of the Service Honda KX500AF.
Finally, the short wheelbase of the KX250F frame had limitation when
matched to the 500cc powerband.
On the plus side, every rider raved about the
comfort of the KX500AF, especially seasoned 500cc riders. The KX500 of
the olden days was targeted towards the offroad and desert crowd,
meaning that the ergonomics were not necessarily cozy for a
motocrosser. The switch to the KX250F chassis, which was purpose-built
for motocross, was a massive ergonomic improvement over the old KX500
frame.
What surprised us most about our Service Honda
KX500AF bike was that the rear wheel came with a small rim and
110/80-19 tire. The power of the 500cc engine begs to have a wider rim
and larger tire footprint on the rear to maximize traction. Bike
vibration was fairly evident, although most riders hardly noticed any
vibration once they rode a few laps around the track.
VERDICT: WHAT DO WE THINK?
The Service Honda KX500AF is a bike that Kawasaki
should have built and sold ten years ago. Unfortunately, during the
interim four-strokes took over the motocross market and killed
production 500cc two-strokes. It’s a dream to think that the Service
Honda KX500AF could revive the once-strong two-stroke. If you’re
looking for the power of a 500cc two-stroke with the technology of an
aluminum frame, the Service Honda KX500AF is the bike for you.
The Service Honda KX500AF retails for $10,999. For more information, please call (219) 932-3588 or visit www.servicehonda.com.
