Yamaha YZF-R25, Service Manual

Page: 252 / 456

CYLINDER AND PISTONS
5-35
EAS30289
REMOVING THE PISTONS
The following procedure applies to both of the
pistons.
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
the piston pin clips from falling into the crank-
case.
• For reference during installation, put an identi-
fication mark on each piston crown.
• Before removing the piston pin, deburr the pis-
ton pin clip grooves 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 CYLINDERS AND PISTONS
The following procedure applies to both of the
cylinders and pistons.
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
3 2 1
Bore
60.000–60.010 mm (2.3622–
2.3626 in)
Taper limit
0.050 mm (0.0020 in)
Out of round limit
0.050 mm (0.0020 in)
Cylinder bore “C” = maximum of D
1
–D
6
Taper limit “T” = maximum of D
1
or D
2
- maximum
of D
5
or D
6
Out of round limit “R” = maximum of D
1
, D
3
or D
5
- minimum of D
2
, D
4
or D
6