Removing The Piston; Checking The Cylinder And Piston - Yamaha XT250X 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. 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
G
Cylinder wall
G
CYLINDER AND PISTON
Vertical scratches → Rebore or replace the
cylinder, and replace the piston and piston
rings as a set.
2. Measure:
Piston-to-cylinder clearance
G
MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
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.
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
"T" = maximum of D
D
6
"R" = maximum of D
D , D or D
2 4 6
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.
5-26
–D
1 2
or D - maximum of D
1 2 5
, D or D - maximum of
1 3 5
or