Not everyone is a fan of orange, but there is
aftermarket KTM plastic available in an amazing array of colors. The 2018 350SXF is oranger than the 2017 model.
tures and would leak air pressure from one chamber to
the other. This was fixed with a change in seal material.
Unfortunately, that wasn’t the ultimate fix, so WP changed
from its original lip seal to a quad-ring seal. The quad
ring solved lots of problems, but because it had four
small sealing surfaces instead of one large one, repetitive
wear became an issue. For 2018, the WP AER forks have
switched to a larger rhomboid-shaped air seal to replace
2017’s quad-ring seal. The new seal has a unique, slightly
out of square shape that increases surface area for better
sealing and longer wear.
( 4) Damping. For 2018, the compression damping
has been firmed up into the middle. Last year’s fork had
free bleed around the compression shim stack—and this
is where the fluttery feel came from. For 2018, KTM has
put a larger shim (30mm instead of 26mm) against the
mid-speed valve to close off low-speed compression by
eliminating the free bleed. This increases the compression
damping and slows shaft-travel speed in small bumps.
The rebound-damping shim stack remains the same, as
does the oil volume in both legs (200cc). The AER forks
have been re-valved to increase low-speed compression by
roughly 5 percent and to lessen the high-speed compression by roughly 10 percent.
Q: WHAT’S THE BIG DEAL ABOUT THE C4
A: The 350SXF transmission has been upgraded with
a C4 bearing installed to increase reliability; however,
you might wonder what a C4 bearing is. Bearings are
graded, much like olives, into grades that delineate their
internal clearances. One major test of bearing quality is
how far the bearing ring moves radially in relationship
to the other ring. Internal clearance is greater than the
operational clearance because of adjustments needed for
thermal expansion. Bearings have internal clearances that
are identified by the coded suffixes C1, C2, C3, C4 and C5.
To simplify things, C3, C4 and C5 bearings have additional
internal radial clearance to cope with high-speed environ-
ments where excess heat is generated.
Q: WHAT IS A METAL INJECTION MOLDING
A: KTM’s 2018 shift star is not a CNC-machined or
a cast-steel part; instead, it is made with Metal Injection
Molding (MIM). MIM merges plastic injection molding and
powdered metallurgy to build precision parts. It does not
have the traditional constraints of hard-working stainless
steel, nickel iron, titanium and other metals. Instead, the
15-micron metal powder can be heated and injected into
a mold cavity under high pressure to produce a unique
product. During the sintering process, the part is heated to
near the melting point of the material. The molding process
allows complex parts to be shaped in a single step and in
MIM can produce parts that are difficult to manufacture
with tool machinery. The shapes can be more exact and
the tolerances closer with injection-molded metal compared to CNC-machined metal. In the case of KTM’s shift
star, MIM is the perfect solution.
Q: WHY WOULD KTM NITRIDE ITS CLUTCH
A: First things first; nitriding is a heat-treating process
that diffuses nitrogen into the surface of a metal to create a
case-hardened surface. Typical applications include gears,
crankshafts, camshafts, cam followers and valves. Given
that KTM is the only motocross manufacturer to use a
steel clutch basket as opposed to aluminum, the interface
between the metal drive plates of the clutch and the steel
tangs of the clutch basket is the opposite of what happens