Yamaha YZ250 2022, Owner'S Service Manual, Page: 171 / 274

CYLINDER HEAD, CYLINDER AND PISTON
5-9
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.
Top ring
Ring side clearance
0.030–0.065 mm (0.0012–0.0026
in)
Side clearance limit
0.100 mm (0.0039 in)
2nd ring
Ring side clearance
0.030–0.065 mm (0.0012–0.0026
in)
Side clearance limit
0.100 mm (0.0039 in)
End gap limit
0.95 mm (0.0374 in)
G089002
b. Upper of cylinder
Piston pin outside diameter limit
17.975 mm (0.7077 in)
Piston pin bore inside diameter
limit
18.040 mm (0.7102 in)
a
b
G089003
G089004
b
G089005