Mounted Bearing Installation: Five Common Mistakes

1. Over-tightening the housing bolts

The housing bolts hold the unit down; they do not align it. Pulling a distorted frame flat with the bolts bows the housing and pinches the bearing, which shows up as heat and noise within days.

If the frame is not flat, shim it. The bolts should be snug, not used as a clamp.

2. Ignoring shaft alignment between two bearings

Two bearings on one shaft share the load only if their centre lines agree. A shaft that is out of line by more than the self-aligning range loads one bearing edge-on and doubles its stress.

The spherical seat absorbs about ±2° — enough for casting tolerance and slight frame deflection, not enough to correct a badly placed second unit.

3. Fitting onto a damaged or undersized shaft

A shaft with a burr, a worn band or a score line will not give the inner ring a true seat. The ring rocks, the seal lip wears a groove, and grease escapes.

Clean the shaft, check the diameter at the bearing position, and if it is worn, either repair it or fit a sleeve-type unit rather than forcing a set-screw unit over the damage.

4. Over-greasing, or never greasing

Too much grease in a sealed unit pushes the seals outward and can blow them. Too little lets the rolling elements run dry. Neither failure is visible until the bearing is noisy.

Follow the housing or catalogue recommendation for the initial fill, and re-grease on a schedule based on running hours and temperature rather than on guesswork.

5. Hammering the unit into place

Striking a mounted unit to seat it transfers impact through the rolling elements to the raceways, leaving brinelling marks that become spalling later. The damage is done before the machine ever runs.

Press on the ring being fitted — never on the housing or the seal — and use a soft drift if a press is not available.

What good installation looks like

In order:

• Check the frame is flat and the bolt holes line up before the unit goes on.
• Clean and measure the shaft at the bearing seat.
• Slide the unit on by hand; if it needs force, stop and find out why.
• Tighten the locking method to its stated torque, not by feel.
• Align both bearings on the shaft before final tightening.
• Grease to the recommended quantity, then run and listen.