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5-6E
Repair manual KTM MINI 50 air/liquid cooled Art.-Nr. 3.206.028 -E
MARK PISTON CYLINDER AC CYLINDER LC
A 39.455 - 39.460 mm 39.515 - 39.520 mm 39.505 - 39.510 mm
1.5533 - 1.5535 in 1.5557 - 1.5559 in 1.5553 - 1.5555 in
B 39.461 - 39.465 mm 39.521 - 39.525 mm 39.511 - 39.515 mm
1.5535 - 1.5537 in 1.5559 - 1.5561 in 1.5555 - 1.5557 in
C 39.466 - 39.470 mm 39.526 - 39.530 mm 39.516 - 39.520 mm
1.5537 - 1.5539 in 1.5561 - 1.5563 in 1.5557 - 1.5559 in
D 39.471 - 39.475 mm 39.531 - 39.535 mm 39.521 - 39.525 mm
1.5539 - 1.5541 in 1.55663 - 1.5565 in 1.5559 - 1.5561 in
Check pistons
If continuing to use a used piston, check as follows:
1. Check piston bearing surface for pressure marks, piston seizure (light
friction can be removed with a fine emery stone).
2. The piston ring may not jam in the piston ring groove. To clean the
piston ring groove, use an old piston ring or sanding paper (400
grain size).
3. Piston ring anti-rotation device must fit tightly in the piston and may
not be worn.
4. Check piston ring for wear and gaps in the cylinder.
Measuring the piston ring end gap
– Insert the piston ring in the cylinder and align with the piston
(approx. 10 mm / 0.39 in under the upper edge of the cylinder).
– Measure end gap
B with a feeler gauge.
End gap: max. 0.20 mm / 0.0078 in
NOTE: If the end gap is larger than specified above, pistons and
cylinder must be checked for wear. If the piston wear and cylinder wear
are within the tolerance zone, the piston ring must be replaced.
Measure the piston and cylinder, determine the piston
– To determine cylinder wear, measure the cylinder 10 mm and 50
mm from the top using a micrometer (shown in the drawing).
– Measure the cylinder diameter in the X and the Y axis to establish
any ovality.
– The piston is measured at the piston skirt, transverse to the piston
pin 32 mm below the top, as shown in the illustration.
– The smallest cylinder diameter minus the largest piston diameter
determines the piston fitting clearance.
Piston fitting clearance AC-engine: 0.055 - 0.065 mm
(0.00216 - 0.00256 in)
LC-engine: 0.045 - 0.055 mm
(0.00177 - 0.00216 in)
NOTE:
When replacing piston and cylinder always make sure to use a piston
and cylinder of the same type. The type identification mark (A to D) can
be found on the cylinder base or the piston head, respectively.
The table to the right indicates the tolerance thresholds for the listed
components.
Always keep in mind that a minimum piston fitting clearance of
0.055 mm (0.00216 in) (AC-engine) or 0.045 mm (0.00117 in)
(LC-engine) is required.