Inspect your carbon brushes at least once every 40 hours of use, or as conditions warrant.  The two carbon motor brushes in your Cyclo are wear items and will need to be replaced after approximately 50 to 150 hours of use.

When they need to be replaced, they will abruptly shut your polisher off, so if you intend to use your polisher heavily, you will probably want to plan ahead and buy a couple replacement brushes to keep on hand to avoid delays in the middle of your job. 

They're very easy to replace and you should do both at the same time.

While you're at it, there are a couple other bits of maintenance you should perform regularly:

• After every 8 hours of use, Lubricate the upper motor bearing by placing 3 drops of light machine oil (e.g. 3-in-1 oil) in the center of the bronze bushing found at the top of themotor housing.
• After every 8 hours of use, or as conditions warrant, blow out the motor housing with compressed air to clean out any accumulated dust, cotton fuzz, dirt or other debris.  If the tool is being used to clean carpets, be sure to blow out the motor housing after each use.  And if the tool gets wet, blow out the underside of the tool.