The addition of spacers between the bearings of a set may be necessary when the following is required:

  • increased angular rigidity by separating the bearing
  • heat generated by the bearings is to be dissipated more effectively
  • the space is required for oil jet nozzles.

Spacer manufacture requires good accuracy to ensure:

  • parallel and planar faces within reduced tolerance limits (Cf. Bearing tolerances)
  • equal width outer and inner spacers to keep bearing original preload unchanged (simultaneous grinding is recommended)
  • well balanced rotated spacer.

The use of appropriate surface hardened (45HRc) or through hardening material is normally recommended. This treatment prevents the risk of spacer surface damage during assembly and wear during subsequent operation.

Many materials are suitable for producing spacers, including the following:

  • ISO 100 Cr6 (SAE 52100) : through hardened
  • UNI 38 Ni Cr Mo 4 (SAE 9840) : through hardened/tempered
  • UNI 18 Ni Cr Mo 7 (SAE 4320) : case hardened

Spacer configuration complexity depends on any other function it may have.

The rotating or static spacer of oil lubricated bearings may, for instance, be deflector shaped to facilitate oil flow through the bearings to ensure good oil drainage and disposal via the discharge channels. It must never restrict lubricant flow.

Spacer configuration in grease lubricated bearings plays a secondary role. The spacer shape must however be such as to allow dispersal of the excess grease expelled by the bearings, especially during the running stage.

Preload arrangements of Back to Back (DD) or Face to Face (FF) can be modified by changing outer or inner space width.

For instance, reducing the width of the spacer placed between the outside rings, causes:

  • reduced preload in DD sets
  • increased preload in FF sets

The opposite occurs by reducing the width of the spacer between the inner rings.
The following calculation is used for proper adjustment: