Yamaha WR250F Manuel D'atelier page 356

CYLINDER AND PISTON
REMOVAL POINTS
Piston and piston ring
1. Remove:
Piston pin clip 1
G
Piston pin 2
G
Piston 3
G
NOTE:
Put identification marks on each piston head
G
for reference during reinstallation.
Before removing each piston pin, deburr the
G
clip groove and pin hole area. If the piston
pin groove is deburred and the piston pin is
still difficult to remove, use the piston pin
puller set 4.
Piston pin puller set:
YU-1304/90890-01304
CAUTION:
Do not use a hammer to drive the piston
pin out.
2. Remove:
Piston ring 1
G
NOTE:
Spread the end gaps apart while at the same
time lifting the piston ring over the top of the
piston crown, as shown in the illustration.
INSPECTION
Cylinder and piston
1. Inspect:
Cylinder and piston walls
G
Vertical scratches → Replace cylinder
and piston.
2. Measure:
Piston-to-cylinder clearance
G
Measurement steps:
1st step:
Measure the cylinder bore "C" with a cylin-
G
der bore gauge.
NOTE:
Measure the cylinder bore "C" in parallel to
and at right angles to the crankshaft. Then,
find the average of the measurements.
4 - 44
ENG