KTM 250 SX-F 2005 Repair Manual page 55

A
B
B
Piston
– Replace the piston if oil consumption is high or the piston skirt is
excessively grooved.
– If the piston is to be remounted:
1. Check the piston bearing surface for damage
2. Piston ring grooves: the piston rings must move freely in the groove.
Use old piston rings or sandpaper (400 grit) to clean the piston ring
grooves.
3. Check the piston rings for damage and end gap.
4. Replace piston pins that are badly discolored or have visible running
marks. Place the piston pin in the conrod and check for clearance.
Piston ring end gap
– Insert the piston ring in the cylinder and align with the piston
(approx. 10 mm under the upper edge of the cylinder).
– Use a feeler gauge to measure the end gap.
A
Compression ring : max. 0.80 mm
Oil scraper ring : max. 1.00 mm
If the end gap is larger than indicated above, check the cylinder for
wear. If the cylinder wear is within the tolerance limits, replace the
piston ring.
Checking the oil pumps for wear
– Insert the inner and outer rotors in the engine case with the marks
facing the case. The marks should no longer be visible when
mounted.
– Use a feeler gauge to measure the wear:
B
Outer rotor - oil pump housing: max. 0.20 mm
Outer rotor - inner rotor: max. 0.20 mm
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