title_body: When to replace bearings in a brushless motors? When, if ever, should I replace the bearings in my drone's brushless motors? Are there signs that a motor needs new bearings?
upvoted_answer: Learning how to replace bearings is a skill worth having.  
  
  It doesn't take much slop in a bearing to add a lot of noise to the gyro signal, and that will be amplified by the PIDs, causing hot motors or reduced performance.  
  
  If the quad is a high-performance or cinematic machine, its best to replace bearings as soon as they sound rattly or get free play in the bearings.
  
  For everyday park fliers, it matters a lot less.  The correct answer is that you change them according to your ability to do the job, and the need for it.