Yamaha YZ450FX 2019, Owner'S Service Manual

Page: 233 / 388

CYLINDER AND PISTON
5-34
EAM30099
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.
3. Measure:
• Piston pin bore inside diameter “b”
Out of specification

Replace the piston.
EAM30100
INSTALLING THE PISTON AND CYLINDER
1. Install:
• Oil ring expander “1”
• Lower oil ring rail “2”
•
Upper oil ring rail “3”
•
2nd ring “4”
•
Top ring “5”
TIP
Be sure to install the piston rings so that the
manufacturer’s marks or numbers face up.
2. Install:
• Piston “1”
•
Piston pin “2”
• Piston pin clip “3”
TIP
•
Apply molybdenum disulfide oil to the piston
pin.
•
Install the piston with the mark “a” on it pointing
to its exhaust (rear) side.
•
Before installing the piston pin clip, cover the
crankcase opening with a cloth to prevent the
b. Upper of cylinder
Piston pin outside diameter
17.991–18.000 mm (0.7083–
0.7087 in)
Limit
17.981 mm (0.7079 in)
Piston pin bore inside diameter
18.004–18.015 mm (0.7088–
0.7093 in)
Limit
18.045 mm (0.7104 in)
a
b
b
New