Bearing Failure Diagnosis Guide | Causes, Symptoms & Prevention (ISO 15243)

Read the symptoms, identify the failure mode (per ISO 15243), fix the root cause. This guide is layered for three audiences: plain notes for newcomers, tables and mode cards for engineers, and "for buyers" notes for procurement.

Most bearings are removed long before they reach their natural fatigue life, and nearly every premature failure traces back to a handful of causes: lubrication problems, contamination, mounting errors, misalignment, overload and electrical damage.

On this page

Quick symptom index
Grease & lubrication signs
The failure modes (ISO 15243)
1. Rolling-contact fatigue
2. Wear
3. Corrosion
4. Electrical erosion
5. Plastic deformation
6. Fracture & cracking
Prevention checklist

Quick symptom index

Start here: match what you hear, feel or see to the most likely cause and failure mode.

Symptom	Most likely cause(s)	Failure mode
Continuous high-pitched squeal / whistle	Inadequate or wrong lubricant; clearance too tight	Wear / preload
Rumbling, growling, gritty rotation	Contamination; raceway wear or corrosion	Wear / corrosion
Regular clicking or knocking (once per rev)	Dent or spall on raceway / rolling element	Fatigue / brinelling
Overheating	Over- or under-lubrication; excessive preload or tight fit; misalignment	Lubrication / deformation
Rising vibration	Contamination; spalling; wear; false brinelling; looseness	Several
Brown/red staining or rust	Moisture ingress	Corrosion
Grey/dark fluting (washboard) marks	Electrical current passage	Electrical erosion
Blue/brown discoloured rings	Overheating / lubricant breakdown	Thermal cracking

Grease & lubrication signs

The condition of the grease is often the quickest clue to what went wrong inside the bearing.

Condition of grease	What it suggests
Darkened, blackened, burnt smell	Overheating or oxidation; lubricant past life, or over-lubrication.
Hard, dry, crusty	Lost base oil / over-aged; re-lubrication interval too long.
Milky or emulsified	Water ingress — check seals and environment.
Gritty between fingers	Solid contamination — abrasive wear occurring.
Metallic sheen / fine metal	Active wear or early spalling.

In plain termsLubrication and contamination together cause the large majority of premature failures. If you remember nothing else: use the right grease, the right amount, on time — and keep dirt and water out.

The failure modes (ISO 15243)

ISO 15243 classifies bearing damage into six groups. Identifying the mode tells you the root cause — and fixing the cause is what stops the failure recurring after replacement.

1. Rolling-contact fatigue

AppearanceFlaking, pitting or spalling — material breaking away from the raceway or rolling elements. May start below the surface (normal end of life) or at the surface where dents or poor lubrication concentrate stress.

Root causesNatural fatigue at end of life; or accelerated by overload, contamination dents, or too thin a lubricant film.

ActionReplace. If it appeared early, correct overload, contamination and lubrication or the new bearing fails the same way.

2. Wear (abrasive & adhesive)

AppearanceAbrasive: dull, matt, scratched surfaces from hard particles. Adhesive (smearing): material transferred and smeared, often discoloured, when surfaces slide under poor lubrication.

Root causesContamination (dirt, dust, debris); inadequate or wrong lubricant; sliding under load with too little oil film.

ActionImprove sealing and cleanliness; correct lubricant type, quantity and interval; eliminate the contamination path.

3. Corrosion (moisture & frictional)

AppearanceMoisture corrosion: red/brown staining and pitting. Fretting corrosion: reddish-brown oxide at fit surfaces from micro-movement. False brinelling: shallow dents at rolling-element spacing from vibration while stationary.

Root causesWater/condensation ingress; poor sealing; loose fits; vibration during transport or standstill.

ActionUpgrade seals; control condensation in storage; correct the fit; protect idle and in-transit machines; use the correct preservative on stored bearings.

4. Electrical erosion

AppearanceTiny arc craters; over time, regular grey/dark fluting (washboard) marks across the raceway, and darkened grease.

Root causesStray current through the bearing — common on variable-frequency-drive (VFD) motors, and from poor earthing or welding currents.

ActionProvide a proper current path: shaft grounding rings, insulated (ceramic-coated or hybrid) bearings on the affected end, correct earthing. Never weld with the return path through a bearing.

5. Plastic deformation

AppearanceTrue brinelling: dents at rolling-element spacing from static overload or impact. Debris/handling indentations: scattered dents from particles or rough handling.

Root causesHammering or pressing on the wrong ring; shock load; dropping the bearing; hard debris in the raceway.

ActionPress only on the interference-fitted ring; use the correct sleeve, press or induction heater; keep clean; never load through the rolling elements.

6. Fracture & cracking

AppearanceCracked or split rings; chipped flanges; in thermal cracking, discoloured rings with cracks across the raceway.

Root causesForced fracture: excessive mounting force / oversized interference. Fatigue fracture: stress concentration over time. Thermal cracking: friction heat (slipping fit, severe under-lubrication).

ActionVerify shaft/housing tolerances against the catalogue; mount with controlled force or heat (not flame); address the heat source for thermal cracking.

For buyers & replacementsWhen ordering a replacement, build the failure lesson into the spec: if heat was the issue, confirm the right clearance (often C3); if contamination, move from shields to contact seals (2RS); if a VFD motor with fluting, quote an insulated or hybrid bearing. For obsolete or hard-to-find sizes, the Bearings Exchange is the place to source them.

Prevention checklist

Stage	Do this
Storage	Keep in original packaging, clean, dry and vibration-free; rotate stock (oldest first); avoid temperature swings that cause condensation.
Handling	Minimise handling; keep hands, tools and bench clean; never drop or knock; leave wrapped until fitting.
Mounting	Check and deburr shaft and housing; verify fits against the catalogue; apply force only to the press-fitted ring; use the correct sleeve, press or induction heater — never a flame, never through the rolling elements.
Lubrication	Use the specified grease type, quantity and interval; do not over-grease (especially at speed); do not mix incompatible greases; keep lubricant clean.
Alignment & fit	Align shaft and housing; use a self-aligning type where misalignment is unavoidable; confirm the right clearance for the operating temperature.
Environment & sealing	Match the seal to the environment; keep out water, dust and process media; protect idle machines from vibration.
Electrical (VFD motors)	Provide shaft grounding and/or insulated bearings; ensure proper earthing; never route welding current through a bearing.
Monitoring	Trend temperature, noise and vibration; investigate a steady rise early; inspect grease at service intervals.

Bearing Failure Guide