KTM 250 SX-F 2005, Repair Manual

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5-7
Nikasil cylinder coating
Nikasil is the brand name for a cylinder coating process developed by
the Mahle piston company. The name is derived from the two materials
used in the process - one layer of nickel in which the exceptionally
hard silicon carbite is embedded. The major advantages of the Nikasil
coating include its outstanding heat dissipation and the improved
power output, the insignificant wear and low weight of the cylinder. It
is inexpensive to repair (replace) a worn coating if the cylinder barrel is
not damaged.
Measuring the piston and cylinder, establishing the mounting
clearance of the piston
– To establish the wear to the cylinder, use a micrometer to measure
the cylinder in the middle of the bearing surface.
– Measure the diameter of the cylinder in the X and the Y axis to
detect any ovality.
Cylinder diameter Size I: 76.000 - 76.012 mm
Size II: 76.013 - 76.025 mm
NOTE: mark the cylinder size
1
on the side of the cylinder, the piston
size
2
on the piston head.
– The piston is measured at the piston skirt across the piston pin, as
illustrated.
Piston diameter Size I: 75.960 - 75.970 mm
Size II: 75.971 - 74.980 mm
– The piston mounting clearance is the difference between the
smallest cylinder diameter and the piston diameter.
Piston mounting clearance Size I: 0.030 - 0.052 mm
Size II: 0.032 - 0.055 mm
Wear limit: 0.070 mm
x
y
1
2