Yamaha YZ250F(S) Owner's Service Manual page 344

CYLINDER AND PISTON
Piston pin
1. Inspect:
Piston pin
G
Blue discoloration/grooves → Replace,
then inspect the lubrication system.
2. Measure:
Piston pin-to-piston clearance
G
Measurement steps:
Measure the outside diameter (piston pin)
G
a.
If out of specification, replace the piston
pin.
Outside diameter (piston pin):
15.991 ~ 16.000 mm
(0.6296 ~ 0.6299 in)
Measure the inside diameter (piston) b.
G
Inside diameter (piston):
16.002 ~ 16.013 mm
(0.6300 ~ 0.6304 in)
Calculate the piston pin-to-piston clear-
G
ance with the following formula.
Piston pin-to-piston clearance =
Inside diameter (piston) b –
Outside diameter (piston pin) a
If out of specification, replace the piston.
G
Piston pin-to-piston clearance:
0.002 ~ 0.022 mm
(0.0001 ~ 0.0009 in)
<Limit>: 0.07 mm (0.003 in)
ASSEMBLY AND INSTALLATION
Piston ring and piston
1. Install:
Piston ring
G
Onto the piston.
NOTE:
Be sure to install the piston rings so that the
G
manufacturer's
located on the upper side of the rings.
Lubricate the piston and piston rings liberally
G
with engine oil.
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