Yamaha YZ450FX 2021, Owner'S Service Manual

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CYLINDER AND PISTON
5-34
d. If out of specification, replace the cylinder,
the piston, and the piston rings as a set.
e. Calculate the piston-to-cylinder clearance
with the following formula.
f. If out of specification, replace the cylinder,
the piston, and the piston rings as a set.
EAM30098
CHECKING THE PISTON RINGS
1. Measure:
• Piston ring side clearance
Out of specification

Replace the piston
and piston rings as a set.
TIP
Before measuring the piston ring side clearance,
eliminate any carbon deposits from the piston
ring grooves and piston rings.
2. Install:
• Piston ring
(into the cylinder)
TIP
Use the piston crown to level the piston ring near
bottom of cylinder “a”, where cylinder wear is
lowest.
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.
Diameter
96.955–96.970 mm (3.8171–
3.8177 in)
Measuring point (from piston
skirt bottom)
9.0 mm (0.35 in)
Piston-to-cylinder clearance =
Cylinder bore “C” - Piston diameter
Piston-to-cylinder clearance
0.010–0.045 mm (0.0004–0.0018
in)
Limit
0.15 mm (0.006 in)
b
a
Top ring
Ring side clearance
0.015–0.065 mm (0.0006–0.0026
in)
Side clearance limit
0.120 mm (0.0047 in)
2nd ring
Ring side clearance
0.020–0.060 mm (0.0008–0.0024
in)
Side clearance limit
0.100 mm (0.0039 in)
Top ring
End gap limit
0.55 mm (0.0217 in)
2nd ring
End gap limit
0.85 mm (0.0335 in)