Cylinder And Piston; Removing The Piston; Checking The Cylinder And Piston - Yamaha WR250F 2016 Owner's Service Manual

REMOVING THE PISTON

EAS2GB7257
1. Remove:
• Piston pin clip "1"
• Piston pin "2"
• Piston "3"
ECA
NOTICE
Do not use a hammer to drive the piston pin
out.
TIP
• Before removing the piston pin clip, cover the
crankcase opening with a cloth to prevent the
piston pin clip from falling into the crankcase.
• Before removing the piston pin, deburr the
piston pin clip's groove and the piston pin's
bore 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
90890-01304
Piston pin puller
YU-01304
1
2. Remove:
• Top ring
• Oil ring
TIP
When removing a piston ring, open the end gap
with your fingers and lift the opposite end gap
of the piston ring over the piston crown.

CYLINDER AND PISTON

CHECKING THE CYLINDER AND PISTON

EAS2GB7258
1. Check:
• Piston wall (Sidewall)
• Cylinder wall
Vertical scratches  Replace the cylinder,
and replace the piston and piston rings as a
set.
2. Measure:
• Piston-to-cylinder clearance
▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
a. Measure the cylinder bore with the cylinder
bore gauge.
TIP
Measure cylinder bore by taking side-to-side
and front-to-back measurements of the cylin-
der.
Bore
77.000–77.010 mm (3.0315–
3.0319 in)
Taper limit
0.050 mm (0.0020 in)
Out of round limit
0.050 mm (0.0020 in)
Cylinder bore = maximum of D
D , D
5 6
Taper limit (front-to-back) = maximum differ-
ence between D
Taper limit (side-to-side) = maximum differ-
ence between D
Out of round limit (top) = difference between
D , D
1 2
Out of round limit (middle) = difference be-
tween D , D
3 4
Out of round limit (bottom)= difference be-
tween D , D
5 6
6-31
, D , D
1 2
, D , D
1 3 5
, D , D )
2 4 6
, D ,
3 4