User Guide

Repair manual KTM 250-525 SX, MXC, EXC RACING Art.-No. 3206007 -E
5-8C
Cylinder – Nikasil coating
Nikasil is the brand name for a cylinder coating process, developed by the
piston manufacturer Mahle. The name is derived from the two
materials used in this process - a nickel layer into which the particularly
hard silicon carbide is embedded. The main advantages of the Nikasil
coating are excellent heat dissipation and thus better power output, low
wear and low weight of the cylinder. The worn coating can be
regenerated at low cost provided that the running surface of cylinder is
flawless.
Measuring piston and cylinder, determining the piston
fitting clearance
– In order to determine the wear of the cylinder, measure the cylinder
center of the running area with a micrometer.
– Measure the diameter of the x-axis and the y-axis in order to check for
oval wear, if any.
Cylinder diameter 250 size I: 75.000 - 75.012 mm
size II: 75.013 - 75.025 mm
Cylinder diameter 400/ size I: 89.000 - 89.012 mm
450 EXC/MXC size II: 89.013 - 89.025 mm
Cylinder diameter 520/ size I: 95.000 - 95.012 mm
450 SX / 525 size II: 95.013 - 95.025 mm
NOTE: The size of the cylinder 1 is marked on the cylinder, the size of
the piston is marked at the top of the piston 2.
– The piston is measured on the piston skirt across to the piston pin as
shown in the illustration.
Diameter of piston 250 size I: 74.960 - 74.970 mm
size II: 74.971 - 74.980 mm
Diameter of piston 400 size I: 88.930 - 88.940 mm
size II: 88.941 - 88.950 mm
Diameter of piston 450 EXC/MXC
size I: 88.916 - 88.946 mm
size II: 88.926 - 88.956 mm
Diameter of piston 520 size I: 94.942 - 94.950 mm
size II: 94.951 - 94.958 mm
Diameter of piston 450 SX / 525
size I: 94.932 - 94.960 mm
size II: 94.940 - 94.968 mm
– The cylinder diameter minus the piston diameter yields the piston
assembly clearance.
Piston assembly clearance 250 piston size I: 0.030 - 0.052 mm
piston size II: 0.032 - 0.055 mm
wear limit: 0.12 mm
Piston assembly clearance 400 piston size I: 0.060 - 0.082 mm
piston size II: 0.062 - 0.085 mm
wear limit: 0.12 mm
Piston assembly clearance size I: 0.054 - 0.096 mm
450 EXC/MXC piston size II: 0.056 - 0.099 mm
wear limit: 0.12 mm
Piston assembly clearance 520 piston size I: 0.050 - 0.070 mm
piston size II: 0.054 - 0.075 mm
wear limit: 0.12 mm
Piston assembly clearance piston size I: 0.040 - 0.080 mm
450SX/525 piston size II: 0.044 - 0.085 mm
wear limit: 0.12 mm
NOTE: Dimensions in Inch see Technical Specification.
x
y
1
2