Yamaha WR450F(R) Owner's Service Manual page 169

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):
17.991 ~ 18.000 mm
(0.7083 ~ 0.7087 in)
Measure the inside diameter (piston) b.
G
Inside diameter (piston):
18.004 ~ 18.015 mm
(0.7088 ~ 0.7093 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:
0.004 ~ 0.024 mm
(0.00016 ~ 0.00094 in)
<Limit>: 0.07 mm (0.003 in)
ASSEMBLY AND INSTALLATION
Piston
1. Install:
Piston rings
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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