Yamaha YZ450F, Owner'S Service Manual

Page: 334 / 650

4 - 47
ENG
CYLINDER AND PISTON
Piston pin
1. Inspect:
• Piston pin
Blue discoloration/grooves
→
Replace,
then inspect the lubrication system.
2. Measure:
• Piston pin-to-piston clearance
ASSEMBLY AND INSTALLATION
Piston
1. Install:
• Piston rings
Onto the piston.
NOTE:
• Be sure to install the piston rings so that the
manufacturer’s marks or numbers are
located on the upper side of the rings.
• Lubricate the piston and piston rings liberally
with engine oil.
Measurement steps:
• Measure the outside diameter (piston pin)
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
.
Inside diameter (piston):
18.004 ~ 18.015 mm
(0.7088 ~ 0.7093 in)
• Calculate the piston pin-to-piston clear-
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.
Piston pin-to-piston clearance:
0.004 ~ 0.024 mm
(0.00016 ~ 0.00094 in)
<Limit>: 0.07 mm (0.003 in)