Most field failures traced to roller bearings — brinelling on shipment, premature spalling, cage fracture, or skewed load zones — start with installation errors, not metallurgy [S2]. A correctly executed mount pairs an ISO 492 radial runout class with a defined shaft/housing tolerance, applies force to the ring with the interference fit, and sets pre-load against a number a torque wrench can read.
Roller bearings span cylindrical, needle, tapered, spherical, and four-row crossed types, with bore sizes from 12.7 mm (NTN 3xxxx single-row) up to 1,270 mm ID and 1,435 mm OD on large cylindrical series, and roller-bearing linear guideways now reaching 4,000 mm rail lengths and 572,700 N load ratings on the HIWIN CRG heavy-duty series [S1][S2]. Knowing the family drives the mounting method: a solid cylindrical roller sleeve is pressed by inner ring, a tapered roller bearing is set by axial nut torque, a self-aligning spherical unit tolerates shaft deflection up to ~1.5° [S5].
Match Shaft and Housing Tolerances to the Bearing Class First
The single most consequential decision in a roller-bearing install is choosing shaft and housing fits from the manufacturer's table, not from habit. For metric radial bearings ISO 492 defines tolerance classes Normal, P6, P5, P4 and running accuracy grades; ISO 492 also sets the limits for bore and OD deviations that the surrounding metalwork must hit. A cylindrical roller bearing on a rotating shaft typically takes a transition or tight transition fit on the inner ring (e.g. k5 or k6 for normal load, m6 for heavier or vibration-loaded service), while the housing is a loose transition or clearance fit (H6, H7, J6) so the outer ring can creep and re-distribute load [S2].
Get the fits wrong and the bearing either slips on the shaft — abrasive wear, fretting corrosion, and rapid failure — or it is so tight on the housing that thermal expansion pre-loads the bearing and the rolling elements never see a uniform load zone. For tapered roller bearings, the shaft seat also defines the axial adjustment travel: too tight and the installer cannot reach the specified assembly torque without over-stressing the rollers. Practical acceptance: measure the shaft and housing with a bore gauge and micrometer before mounting, and reject any feature outside the bearing maker's published limit.
Apply Mounting Force to the Correct Ring, with the Correct Tool
Mechanical pressing works only when force is delivered to the ring with the interference fit. A solid cylindrical or needle bearing pressed onto a shaft must be driven on the inner ring; pressing on the outer ring transmits load through the rolling elements and produces brinelling or raceway damage in seconds [S2]. For shaft diameters above ~50–80 mm or where a tight interference fit raises the required force beyond what a hand press can deliver, induction heaters are standard — heating the inner ring to +80–120 °C above shaft temperature expands it enough to slide on without force.
For housed units, a hydraulic or mechanical puller is the safe extraction tool; hammering on the housing transmits shock through the rolling elements and cracks the cage. Cold mounting with a mallet is acceptable only on small bearings (bore under ~30–40 mm) with light interference, and even then the strike should land on a sleeve that contacts the ring face squarely. Acceptance: after mechanical mount, rotate the bearing by hand — it must turn smoothly without grinding, binding, or notch feel. Any hesitation or roughness is a stop-work signal; do not proceed to lubrication or coupling alignment until the bearing rotates freely.
Set Tapered and Pre-Loaded Roller Bearings by Measurable Numbers
Tapered roller bearings are not "fitted to feel"; they are adjusted to a number. The conventional method is to torque the locknut while rotating the bearing so the rollers seat on the cone and cup, then back off to the published clearance or to the prescribed assembly torque. For a four-row tapered roller CRO/CROU series (NTN), bore ranges from 120 mm to 938.21 mm and OD from 170 mm to 1,270 mm, and the mill must apply the OEM's clearance table — typically measured with a feeler gauge across the outer race after the nut is set, and confirmed by rotating torque [S2].
Pre-loaded pairs — for machine-tool spindles, crossed-roller guides, or four-row recirculating roller linear guides — are set against either a defined axial load (C0a figure on the data sheet) or a measured starting torque on the nut. The CRG four-row recirculating roller linear guide for example spans 11,300 N to 572,700 N static load ratings across its 45 mm range, and the block must be seated on the profiled rail using the cover-strip installation aid to keep the mounting holes sealed [S1]. Acceptance: log the torque or the feeler-gauge reading on the build sheet; without that number, a future failure analysis cannot tell whether the bearing was correctly adjusted or simply tightened "until it stopped."
Align, Lubricate, and Verify Before Coupling the Load
Misalignment is the second leading cause of early roller-bearing death after bad fits. For shaft-to-shaft coupling, dial-indicator check the coupling hubs: typical acceptance is ≤0.05 mm parallel offset and ≤0.05 mm/100 mm angular offset for flexible couplings on precision roller-bearing assemblies, with limits relaxed to ~0.1–0.2 mm for general industrial service depending on coupling type. A self-aligning spherical or toroidal roller bearing forgives shaft deflection up to roughly 1–1.5° and so is the right pick when the structure cannot hold tighter alignment [S2][S5].
For oil-mist or oil-bath installations, flood the bearing at standstill so oil is present at the contact zone on the first turn. Acceptance: run the machine uncoupled for a defined no-load period (often 30–60 minutes), monitor bearing housing temperature with a calibrated probe or IR thermometer, and confirm temperature rise stabilises below the OEM limit (commonly ≤50 °C above ambient for grease-lubricated units). Coupling the load before this stabilisation is a common way to score a raceway inside the first hour.
When to Stop Repairing and Replace the Bearing
A bearing that has run hot enough to discolour the cage, that shows measurable brinelling (indentations on the raceway from impact), or whose radial play has grown by more than roughly 2× the as-installed value is past in-service repair. Spalling, fluting, or any electrical-discharge pitting (micro-cratering in regular patterns from VFD-induced shaft currents) means the bearing must be replaced and the root cause (grounding ring, insulated bearing, VFD cable routing) addressed before the next unit goes in [S2].
For linear roller guideways, the same rule applies: a single spalled race segment on a CRG-class rail compromises the whole rail length, and a replacement block on a worn rail shortens the new block's life. In all cases, the more useful engineering artefact is the build sheet — fits measured, mounting method, torque or clearance value, alignment numbers, run-in temperatures — so the next install is repeatable rather than a re-enactment of the last one. For a deeper look at selecting among the families above, see Roller Bearing Types and Classifications: A Working Engineer's Reference; for a primer on the closely related linear guide architecture behind the CRG series, see linear guide; and for load-zone geometry on the rolling element itself, see roller bearing.
For component-level specifications, see crossed roller guide.