Motor Bearing Noise — Root Cause Analysis & 8D Guide

Symptoms Abnormal noise: humming, grinding, squealing; increases with RPM Vibration 2× baseline; raceway spalling on disassembly Bearing housing temperature 10–30°C above normal Affected Components AC induction, PMSM, BLDC motors; deep groove ball bearings Bearing housing, shaft journals, lubricant seals Detection Methods Vibration FFT: BPFO, BPFI, BSF, FTF frequencies Acoustic Emission/Ultrasound: High-frequency stress waves Oil Analysis: Wear particle concentration Thermography: Hot spots at bearing housing Possible Causes Insufficient lubrication (wrong viscosity, contamination, degradation) Overload/fatigue exceeding dynamic load rating Misalignment > 0.05mm; contamination through damaged seals Electrical erosion from VFD shaft currents Improper mounting (hammer installation, excessive interference) 5-Why Example Problem: 85 dB noise at 3000 RPM after 800h Why noisy? → Inner raceway spalling fatigue Why spalling? → Boundary lubrication film breakdown Why breakdown? → Grease contaminated with moisture Why moisture? → Seal lip wear from washdown water ingress Why undetected? → No seal inspection in PM schedule TRC: Water ingress through worn seal contaminating grease MRC: PM schedule lacked seal inspection and replacement interval Fishbone (6M) Man: Washdown spray directly at bearing area Machine: 0.03mm shaft runout contributing to seal wear Method: No grease replenishment after washdown Material: NBR seal degraded by alkaline cleaner; NLGI#2 grease not water-resistant Measurement: Monthly...