Does a bearing locknut always set bearing preload?

The short answer

No. A locknut can retain a bearing ring axially, or it can participate in an arrangement that deliberately sets clearance or preload. Its function depends on the complete stack and bearing design. Tightness of a wind-generator bearing locknut does not independently establish internal preload.

Trace what the nut clamps

A nut may press a ring against a fixed shoulder through a spacer, securing axial location without defining a controlled internal bearing force. In another arrangement, relative ring positions are intentionally adjusted to establish the internal state. The same visible nut can therefore serve different functions. A drawing must identify which faces meet and which components deform or move as the nut advances.

Keep retention force and preload distinct

Axial clamp force in a shaft stack is not automatically equal to rolling-contact preload. Ring contacts, spacers, shoulders and any paired-bearing arrangement determine how force reaches the internal contacts. Nut torque also depends on thread and face friction, so an isolated torque reading cannot recover internal preload. The equipment-specific setting method may use another measured response entirely.

Request the functional stack definition

Ask the generator supplier whether the nut provides retention, bearing setting or both, and request the applicable sectional drawing and approved verification method. SKF arrangement guidance distinguishes axial location from bearing internal conditions; it provides no MARSTON locknut setting. Do not tighten a nut until play disappears or infer a preload value from generic torque tables. The concrete decision is whether the assembly evidence verifies the intended function of that nut in the actual bearing stack. Where a spacer defines relative ring position, its dimensions can govern the internal setting while the nut merely closes the stack. That distinction should be explicit before nut torque is used as an acceptance indicator.