Replace it if necessary.

Inner Tube Inspection
Spring Tension InspectionExternal Shift Mechanism Installation
Install the gear positioning lever [A] as shown in the figure.
Install:
Spring [B]
Washer [C]
Tighten:
Torque - Gear Positioning Lever Bolt [D]: 12 N·m (1.2 kgf·m,
106 in·lb)
Assemble:
Ratchet [A]
Pawls [B]
Pins [C]
Springs [D]
Install the shift ratchet ...
Piston Removal
Remove:
Crankshaft (see Crankshaft Removal)
Remove the piston together with the connecting rod to the
cylinder head side.
NOTICE
Discard the connecting rod bolts and nuts. To prevent
damage to the crankpin surfaces, do not allow
the connecting rod bolts to bump against the
crankpins. ...
Valve Guide Removal
Remove:
Valve (see Valve Removal)
Oil Seal
Spring Seat
Heat the area around the valve guide to 120
150°C (248
302°F), and hammer lightly on
the valve guide arbor [A]
to remove the guide from the top of the head.
NOTICE
Do not heat the cylinder head with a torch. This ...