Removing The Piston; Checking The Cylinder And Piston - Yamaha WR250R Service Manual

EAS24380

REMOVING THE PISTON

1. Remove:
Piston pin clips "1"
G
Piston pin "2"
G
Piston "3"
G
ECA13810
CAUTION:
Do not use a hammer to drive the piston pin
out.
NOTE:
Before removing the piston pin clip, cover the
G
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-
G
ton pin clip's groove and the piston's pin bore
area.
2
2. Remove:
Top ring
G
2nd ring
G
Oil ring
G
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 (Sidewall)
G
Cylinder wall
G
2. Measure:
a. Measure cylinder bore "D" with the cylinder
NOTE:
Measure cylinder bore "D" by taking side-to-side
and front-to-back measurements of the cylinder.
Then, find the average of the measurements.
3
1
b. If out of specification, rebore or replace the
c. Measure piston skirt diameter "P" with the mi-
5-26
CYLINDER AND PISTON
Vertical scratches → Rebore or replace the
cylinder, and replace the piston and piston
rings as a set.
Piston-to-cylinder clearance
G
MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
bore gauge.
Cylinder bore "D"
77.000–77.010 mm (3.031–3.032
in)
Limit
77.100 mm (3.035 in)
Taper limit "T"
0.05 mm (0.002 in)
Out of round limit
0.05 mm (0.002 in)
"D" = maximum of D –D
1 6
"T" = (maximum of D or D
1
cylinder, and replace the piston and piston
rings as a set.
crometer.
a
a. 12 mm (0.47 in) from the bottom edge of the pis-
ton
) - (maximum of D or D )
2 5 6
P