Checking The Piston Pin; Installing The Piston And Cylinder - Yamaha XG250 Service Manual

Piston ring
Top ring
End gap (installed)
0.19–0.31 mm (0.0075–0.0122 in)
Limit
0.60 mm (0.0236 in)
2nd ring
End gap (installed)
0.30–0.45 mm (0.0118–0.0177 in)
Limit
0.60 mm (0.0236 in)
Oil ring
End gap (installed)
0.10–0.35 mm (0.0039–0.0138 in)
EAS24440

CHECKING THE PISTON PIN

1. Check:
Piston pin
●
Blue discoloration/grooves → Replace the
piston pin and then check the lubrication sys-
tem.
2. Measure:
Piston pin outside diameter "a"
●
Out of specification → Replace the piston
pin.
Piston pin outside diameter
15.991–16.000 mm (0.6296–0.6299
in)
Limit
15.970 mm (0.6287 in)
3. Measure:
Piston pin bore diameter "b"
●
Out of specification → Replace the piston.
Piston pin bore inside diameter
16.002–16.013 mm (0.6300–0.6304
in)
Limit
16.043 mm (0.6316 in)
CYLINDER AND PISTON
4. Calculate:
Piston-pin-to-piston-pin-bore clearance
●
Out of specification → Replace the piston pin
and piston as a set.
Piston-pin-to-piston-pin-bore clearance =
Piston pin bore diameter "b" -
Piston pin outside diameter "a"
Piston-pin-to-piston-pin-bore
clearance
0.002–0.022 mm
Limit
0.073 mm
EAS24450

INSTALLING THE PISTON AND CYLINDER

1. Install:
Lower oil ring rail "1"
●
Oil ring expander "2"
●
Upper oil ring rail "3"
●
2nd ring "4"
●
Top ring "5"
●
NOTE:
Be sure to install the piston rings so that the "T"
marks or numbers face up.
5-28
b