Checking The Pistons; Checking The Piston Ring End Gap; Assembly Instructions For Piston Rings; Measuring Pistons/Cylinders, Establishing Piston Mounting Clearance - KTM 2003 950 Adventure Repair Manual

A
x
y

Checking the pistons

– Mark the position of the piston arrow in the cylinder to facilitate
reassembly and to ensure that the same piston is mounted in the
same cylinder again.
– Press the piston up out of the cylinder.
– Replace the piston if oil consumption is high or the piston skirt is
excessively grooved.
– If the piston is to be reinstalled:
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. The piston pins must move freely in the bolt hole when mounted.
Replace piston pins that are badly discolored or have visible running
marks. Place the piston pin in the conrod and check for clearance.
Maximum clearance in the conrod eye: 0.08 mm.
NOTE: the piston pin may not have any clearance when mounted and
should be easy to move when applying slight counterpressure.

Checking the 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).
– Measure the end gap with a feeler gauge
Piston ring end gap: max. 0.50 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.

Assembly instructions for piston rings

– Mount the oil scraper ring in the lower piston ring groove with the
mark facing the piston head.
– Mount the compression ring in the middle piston ring groove with
the mark facing the piston head.
– Mount the compression ring in the upper piston ring groove with the
mark facing the piston head.
Measuring pistons and cylinders, establishing the piston
mounting clearance
– To establish cylinder wear, use a micrometer to measure the cylinder
in the middle of the bearing surface.
– Measure the X and Y axis of the cylinder diameter to establish any
ovality.
NOTE: if the Nicasil coating on the cylinder is worn but not damaged, a
replacement cylinder can be ordered from our KTM dealer/importer
(new Nicasil coating, used cylinder).
– Measure the piston at the piston skirt across the piston pin, 9 mm
from the lower edge.
950:
Piston size I: 99.953 mm – 99.967 mm
Piston size II: 99.963 mm – 99.977 mm
Wear limit: 99.930 mm
990:
Piston size I: 100.943 mm – 100.957 mm
Piston size II: 100.953 mm – 100.967 mm
Wear limit: 100.930 mm
– The piston mounting clearance is the difference between the
smallest cylinder diameter and the piston diameter.
Piston mounting clearance 950: 0.04 mm – 0.06 mm
Wear limit: 0.10 mm
Piston mounting clearance 990: 0.05 mm – 0.07 mm
Wear limit: 0.10 mm
5-10
.
A