Yamaha YZ125X 2022, Owner'S Service Manual

Page: 170 / 268

CYLINDER HEAD, CYLINDER AND PISTON
5-10
EAM30548
CHECKING THE PISTON RING
1. Measure:
•
Piston ring side clearance
Out of specification

Replace the piston
and piston ring as a set.
TIP
Before measuring the piston ring side clearance,
eliminate any carbon deposits from the piston
ring grooves and piston ring.
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.
EAM30549
CHECKING THE PISTON PIN
1. Check:
•
Piston pin
Blue discoloration/grooves

Replace the
piston pin, and then check the fuel and en-
gine mixing oil.
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.
4. Calculate:
•
Piston-pin-to-piston-pin-bore clearance
Out of specification

Replace the piston pin
and piston as a set.
Top ring
Ring side clearance
0.035–0.070 mm (0.0014–0.0028
in)
Side clearance limit
0.100 mm (0.0039 in)
End gap limit
1.20 mm (0.0472 in)
b. Upper of cylinder
G089002
a
b
G089003
Piston pin outside diameter limit
14.975 mm (0.5896 in)
Piston pin bore inside diameter
limit
15.040 mm (0.5921 in)
Piston-pin-to-piston-pin-bore clearance =
Piston pin bore inside diameter “b” -
Piston pin outside diameter “a”
G089004
b
G089005