Replace it if necessary.

Inner Tube Inspection
Spring Tension InspectionBalancer Assemble
Apply molybdenum disulfide oil solution to the ribs of the
balancer [A].
Apply molybdenum disulfide oil solution to the ribs of the
balancer gear [A].
Check that the rubber dampers [B] are in place.
Face the linked portion [C] to the bottom.
Assemble the balancer weight ...
Swingarm Bearing Installation
Replace the needle bearings, ball bearing, grease seals
and circlip with new ones.
Install the needle bearings, ball bearing, grease seals and
circlip as shown in the figure.
Insert the needle bearing driver [A] into the needle bearing
[B] and press the needle bearing into the housing u ...
Cylinder (Upper Crankcase) Wear Inspection
Split the crankcase (see Crankcase Splitting).
Remove the pistons (see Piston Removal).
Assemble the cylinder (upper crankcase) [A], the cylinder
head [B] and the cylinder head gasket [C].
Tighten the cylinder head bolts (see Cylinder Head Installation
in the Engine Top End chapter).
...