Yamaha XT250X 2008, Service Manual

Page: 172 / 282

CYLINDER AND PISTON
5-26
EAS24380
REMOVING THE PISTON
1. Remove:
●
Piston pin clips “1”
●
Piston pin “2”
●
Piston “3”
CAUTION:
ECA13810
Do not use a hammer to drive the piston pin
out.
NOTE:
●
Before removing the piston pin clip, cover the
crankcase opening with a clean rag to prevent
the piston pin clip from falling into the crank-
case.
●
Before removing the piston pin, deburr the pis-
ton pin clip’s groove and the piston’s pin bore
area.
2. Remove:
●
Top ring
●
2nd ring
●
Oil ring
NOTE:
When removing a piston ring, open the end gap
with your fingers and lift the other side of the ring
over the piston crown.
EAS24390
CHECKING THE CYLINDER AND PISTON
1. Check:
●
Piston wall
●
Cylinder wall
Vertical scratches
→
Rebore or replace the
cylinder, and replace the piston and piston
rings as a set.
2. Measure:
●
Piston-to-cylinder clearance
▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
a. Measure cylinder bore “C” with the cylinder
bore gauge.
NOTE:
Measure cylinder bore “C” by taking side-to-side
and front-to-back measurements of the cylinder.
Then, find the average of the measurements.
b. If out of specification, rebore or replace the
cylinder, and replace the piston and piston
rings as a set.
c. Measure piston skirt diameter D “a” with the
micrometer.
Bore
74.000
–
74.0µ16 mm
(2.9134
–
2.9140 in)
Wear limit
74.100 mm (2.9173 in)
Taper limit
0.050 mm (0.0020 in)
Out of round limit
0.010 mm (0.0004 in)
“C” = maximum of D
1
–
D
2
“T” = maximum of D
1
or D
2
- maximum of D
5
or
D
6
“R” = maximum of D
1
, D
3
or D
5
- maximum of
D
2
, D
4
or D
6
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