Yamaha MBK MW125 2014, Service Manual

Page: 232 / 380

CYLINDER AND PISTON
5-29
EAS30289
REMOVING THE PISTON
1. Remove:
• Piston pin clips “1”
• Piston pin “2”
• Piston “3”
NOTICE
ECA13810
Do not use a hammer to drive the piston pin
out.
TIP
• Before removing the piston pin clips, cover the
crankcase opening with a clean rag to prevent
them from falling into the crankcase.
• Before removing the piston pin, deburr the pis-
ton pin clip groove and the piston pin bore ar-
ea. If both areas are deburred and the piston
pin is still difficult to remove, remove it with the
piston pin puller set “4”.
2. Remove:
• Top ring
• 2nd ring
• Oil ring
TIP
When removing a piston ring, open the end gap
with your fingers and lift the other side of the ring
over the piston crown.
EAS30291
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.
TIP
Measure cylinder bore “C” by taking side-to-side
and front-to-back measurements of the cylinder.
Then, find the average of the measurements.
Piston pin puller set
90890-01304
Piston pin puller
YU-01304
1
2
3
Bore
52.400–52.425 mm (2.0630–
2.0640 in)
Taper limit
0.050 mm (0.0020 in)
Out of round limit
0.050 mm (0.0020 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
- minimum of D
2
,
D
4
or D
6