Checking The Piston Pin; Installing The Piston And Cylinder - Yamaha YFM70RY Service Manual

3. Measure:
• Piston ring end gap
Out of specification → Replace the piston
ring.
TIP
The oil ring expander spacer's end gap cannot
be measured. If the oil ring rail's gap is exces-
sive, replace all three piston rings.
Top ring
End gap (installed)
0.20–0.35 mm (0.008–0.014 in)
Limit
0.60 mm (0.024 in)
2nd ring
End gap (installed)
0.75–0.90 mm (0.03–0.04 in)
Limit
1.25 mm (0.0492 in)
Oil ring
End gap (installed)
0.20–0.70 mm (0.01–0.03 in)
EAS24440

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
22.991–23.000 mm (0.9052–
0.9055 in)
Limit
22.971 mm (0.9044 in)
3. Measure:
• Piston pin bore diameter "b"
Out of specification → Replace the piston.
CYLINDER AND PISTON
Piston pin bore inside diameter
23.004–23.015 mm (0.9057–
0.9061 in)
Limit
23.045 mm (0.9073 in)
4. Calculate:
• Piston-pin-to-piston-pin-bore clearance
Out of specification → Replace the piston pin
and piston as a set.
• Piston-pin-to-piston-pin-bore clearance =
Piston pin bore diameter "b" –
Piston pin outside diameter "a"
Piston-pin-to-piston-pin-bore
clearance
0.004–0.024 mm (0.0002–0.0009
in)
Limit
0.074 mm (0.0029 in)
EAS24450

INSTALLING THE PISTON AND CYLINDER

1. Install:
• Lower oil ring rail "1"
• Oil ring expander "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.
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