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 InspectionDrive Chain Lubrication Condition Inspection
If a special lubricant is not available, a heavy oil such as
SAE 90 is preferred to a lighter oil because it will stay on
the chain longer and provide better lubrication.
If the chain appears especially dirty, clean it before lubrication.
NOTICE
The O-rings between the side plates seal ...
Safe riding technique
The points given below are applicable for everyday motorcycle use and
should
be carefully observed for safe and effective vehicle operation.
For safety, eye protection and a
helmet are strongly recommended.
You should be aware of and verify
the applicable safety regulations in
force prior ...
Air Switching Valve Removal
NOTICE
Never drop the air switching valve especially on a
hard surface. Such a shock to the air switching
valve can damaged it.
Remove the air cleaner housing (see Air Cleaner Housing
Removal in the Fuel System (DFI) chapter).
Disconnect the connector [A].
Disconnect the hoses [B] from ...