Axial hunting of 2-pole motors: Causes and cures
A common observation about 2-pole machines fitted with sleeve bearings is the inherent weak magnetic centering force. The classic symptom is chronic axial movement: a 2-pole rotor drifting "to and fro" from the established magnetic center position. This article addresses the numerous causes of this phenomenon, colloquially referred to as "hunting." Although the focus is on 2-pole motors, much of this information applies to sleeve bearing motors of any speed rating. Identifying the cause of a problem is good, but solutions are a lot more useful, so I've included those as well.