Bearing and main shaft are common consumable parts of a motor. You are recommended to replace a new one from time to time after a period of flight time.
** Notice: Motor is not exchangeable/refundable if the motor cables are cut (shorten) or motor has apparently damage. So if you want to test the motors to make sure the motors are working properly, we suggest you to use "Terminal Blocks" for connection between motor and ESC for testing. Thank you for your kind attention.