Check the motor shaft spins smoothly by hand and shows no grinding, squealing, or excessive play.

Begin by isolating power and ensuring the blower or fan is locked out before touching the motor. Remove any belts or couplings so the rotor can turn freely and then rotate the shaft slowly with your hand to feel for rough spots, catches, or a grainy texture that indicates pitting or debris on bearings. While turning listen closely for high pitched squeal or low grinding which often means the bearing race or roller elements are wearing. Measure axial end play with a dial indicator or feeler gauge against the shaft housing; more than the manufacturer allowed clearance suggests worn thrust components. Check radial runout by supporting and rotating the shaft and noting any wobble that points to bearing looseness or a damaged journal; if you do not have instruments use a straightedge and steady your eye at a fixed point to detect wobble. Inspect lubrication method: for grease lubricated bearings, confirm grease intervals and quality, repack or replace grease following the motor maker guidance and avoid overfilling which can cause overheating; for oil lubricated systems, check sump level and oil condition and replace with the specified viscosity. Finally review motor temperature during a controlled run after inspection using a contact temperature gun or measured by hand caution, comparing to manufacturer operating range to detect bearing friction related heating.

Common mistakes include rotating the shaft with power applied which risks injury and hides bearing feel so always deenergize and lock out before manual spin. Another frequent issue is over greasing; excess grease increases internal pressure and can degrade seals causing premature failure, so apply only the specified amount and type. A third error is relying solely on noise or vibration without checking axial play and lubrication history which can miss early wear; combine tactile spin, end play measurement, and lubricant inspection for a complete assessment.

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