Checking The Piston Pin; Installing The Piston And Cylinder - Yamaha YZ450FX 2019 Owner's Service Manual

b. Upper of cylinder
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.
Piston pin outside diameter
17.991–18.000 mm (0.7083–
0.7087 in)
Limit
17.981 mm (0.7079 in)
3. Measure:
• Piston pin bore inside diameter "b"
Out of specification  Replace the piston.
Piston pin bore inside diameter
18.004–18.015 mm (0.7088–
0.7093 in)
Limit
18.045 mm (0.7104 in)
a
b
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
5-34
CYLINDER AND PISTON
b
New