one-off Baja and desert bikes that used the sidecar
engine. These one-offs were the impetus to request a
production version of the KTM 550 M/XC.
In motocross, the 1994 KTM 550 M/XC was not a
world beater. Its best attribute was the broad and
usable powerband. Otherwise, the big-bore KTM was
a point-and-steer handler with harsh suspension and a
meager clutch. While the 550 M/XC was innovative,
time was not on its side. Open-class racing had fallen out of favor. The AMA dropped the 500 Nationals
and consumers yearned for agile 250cc two-strokes.
Hence, the KTM 550 M/XC—an albino tiger in the
two-stroke market—was never made in large numbers.
Destiny intervened two decades later when Jeff Moffet
happened across a 1994 KTM 550 M/XC that was for
sale. Jeff gladly spent $1500 on the relic and went to
work creating his monster.
STEP 2: JOINING OLD AND NEW
Don’t think for a second that Moffet was able to
shoehorn the 550 M/XC engine into the 250SXF-
FE frame without making serious modifications.
That would have been too easy. Jeff enlisted Tiginit
Motorsports, a custom off-road fabrication shop in
Medford, Oregon, to create a new frame cradle from
the downtubes to the footpegs. It was imperative
to open up the engine bay to accept the big-block
550cc. Moffet then machined out the swingarm pivot
hole in the back of the engine to allow clearance for
the 250SXF swingarm pivot bolt. New cylinder head
mounts were also necessary. With the engine secured
to the chassis, Jeff encountered his next challenge–
getting air into the induction system.
Things really got tricky. First, Jeff had to get the
stock 550 M/XC airbox onto the 250SXF chassis.
Moffet shaved down the left side of the airbox to
allow enough clearance for the exhaust pipe. The
no-tools airbox side cover hid the modification for a
clean look. The carburetor had to be relocated to avoid
hitting the WP rear shock. A wedge was machined off
the intake flange to move the carburetor out of harm’s
way. Finally, the Factory Edition hydraulic clutch
master cylinder wouldn’t work with the old-school
cable-actuated KTM 550 M/XC clutch system, so Jeff
had to install a new lever, cable and guides.
STEP 3: THE DRIVING FORCE
Of all the steps, turning the rear wheel around was
most intensive. The 1994 KTM 550 M/XC engine’s
countershaft sprocket was on the right side of the bike
and the kickstarter was on the left—as was the tradition with European bikes 20 years ago. Moffet had to
figure out a way to reverse the rear wheel while still
using the 250SXF Factory Edition swingarm. Several
key modifications were required to successfully make
the swap. (1) Rear brake. The 250SXF rear brake
pedal is mounted to the inside of the frame. Given
the 550’s right-side drivetrain, using the 250SXF rear
brake wasn’t possible. Moffet tapped into his wealth of
KTM knowledge to come up with a solution. He dug
through his parts bin and found a rear brake system
off a KTM LC4 640 adventure bike. The caliper design
was dated in comparison to the 250SXF rear brake,
but it provided clearance for the countershaft sprocket.
( 2) Caliper. It was necessary to cut and machine a
tab for the rear brake caliper on the left side of the