Bearings, Seals, and Lubrication
Types and fits
Antifriction bearings include deep-groove ball, cylindrical, spherical and tapered roller, and thrust types. The rotating ring normally takes an interference fit; the stationary ring a lighter fit. Never make both tight. Too loose causes creep and fretting; too tight removes internal clearance and overheats the bearing.
Mounting
Heat with an induction heater or clean oil bath - commonly no more than about 200–250°F, and never above the seal or pre-greased limit. Never use an open flame or hammer. Press only on the ring being fitted (inner ring for a shaft fit). Use hydraulic nuts on tapered bores and verify clearance reduction with a feeler gauge.
Lubrication
Grease: fill roughly one-third of the free space - over-greasing churns, heats, and blows seals. Oil: correct ISO viscosity grade for speed and temperature, correct level, kept clean. Mixing incompatible grease bases can soften or harden the soap. Contamination - water and particles - is the dominant cause of early failure.
Seals
Lip seals face the lubricant with the lip toward the oil side; labyrinth seals depend on clearance and often a purge; mechanical seals need clean, flat faces, a vented gland, and no dry running.
Failure signatures
Spalling and fatigue from overload or misalignment; true brinelling from shock; false brinelling from vibration while stationary; electrical fluting from shaft currents; smearing from skidding.
Traps
Hammering a bearing on, overheating past the seal limit, packing grease to 100%, and installing a replacement with the wrong internal clearance.
Rule of thumb
A correctly installed and lubricated bearing runs cool and quiet. A 20°F rise above its own baseline, or a new whine, is your first warning.