Checking The Piston Rings; Checking The Piston Pin - Yamaha YZ 2023 Series Owner's Service Manual

Diameter
76.955–76.970 mm (3.0297–
3.0303 in)
Measuring point (from piston
skirt bottom)
4.0 mm (0.16 in)
b
a
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.
Piston-to-cylinder clearance =
Cylinder bore "C" - Piston diameter
Piston-to-cylinder clearance
0.030–0.055 mm (0.0012–0.0022
in)
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.
Ring side clearance
0.030–0.065 mm (0.0012–0.0026
in)
Side clearance limit
0.115 mm (0.0045 in)
CYLINDER AND PISTON
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 the oil ring as a set.
Piston ring
Top ring
End gap limit
0.50 mm (0.0197 in)
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.
5-34
a
b