RC How To:
Clean & Maintain a Brushless Motor - 3
Step 5 - Blow the Parts Off
Once your motor is apart, take the components and blow them off with compressed air.
I have my workshop in a controlled environment so I use my air compressor for this, but for those who have outdoor shops and live in a humid environment who might consider canned air. Motor spray is NOT recommended for this.
Blow all of the parts off where you cannot see any dirt, dust, or debris anywhere.
Step 6 - Check the Bearings
Stick the rotor into the bearings and spin it to see if your bearings are grinding or just generally not smooth. If they are, you'll need to replace or clean the bearings. If they are OK, wipe them down with a paper towel or cotton swab.