If any is worn down to the service limit, replace the brush assy.
Starter Motor Brush Length [B] Standard: 12.05 mm (0.4744 in.) Service Limit: 6.55 mm (0.258 in.)

Starter Motor Assembly
Commutator Cleaning and InspectionLiquid Gasket, Non-permanent Locking Agent
For applications that require Liquid Gasket or a
Non-permanent Locking Agent, clean the surfaces so
that no oil residue remains before applying liquid gasket or
non-permanent locking agent. Do not apply them excessively.
Excessive application can clog oil passages and
cause serious damage.
...
Drive Chain Slack Adjustment
Remove the cotter pin [A], and loosen the rear axle nut
[B].
Loosen the both chain adjuster locknuts [C].
If the chain is too loose, turn out the left and right chain
adjusters [D] evenly.
If the chain is too tight, turn in the left and right chain
adjusters evenly, and kick the wheel f ...
Clutch Cover Assembly
Replace the needle bearings and oil seal with new ones.
NOTE
Install the needle bearings so that the manufacture’s
mark face out.
Install the needle bearings [A] and oil seal [B] position as
shown in the figure.
Press the upper and lower bearings so that the bearing
surface [ ...