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Bearing Replacement Is Complicated

08:39AM Jan 03, 2015

Installing a ball bearing and its eccentric lock collar on a shaft is actually complicated if you do it right. When a new bearing is installed on a used shaft, the shaft needs to be cleaned with an emery cloth or wire brush so the bearing smoothly slides into place. 

A new bearing shouldn’t “easily” slide into place—that implies the shaft is worn or the cleaning process was a little too aggressive and removed a few thousandths of an inch of metal from the shaft’s surface. If a new bearing loosely slides on a shaft, or if it can be wobbled on a shaft enough to feel a “click” of free play between the inner race and the shaft, the shaft is undersized and needs to be replaced.

(However, in emergencies and situations of “chronic tightwad,” problems with excess free play between bearings and shafts can sometimes be “fixed” using products, such as Loctite’s Press-Fit Repair 660, designed to fill gaps of up to 0.020 of an inch between components.)

It’s important to align a new bearing with its shaft before tightening its mounting bolts and installing the lock collar. If the bearing is held in place with sheet metal flanges, snug the bolts’ nuts finger-tight. Lift or position the shaft in its normal operating position/height and spin it while lightly tapping on the bearing flanges to encourage the bearing to align with the shaft and within the flanges.

If the bearing is mounted in a pillow-block bearing mount, spin/rotate the shaft as the bearing block’s mounting bolts are installed and tightened. It helps to lightly tap the bearing block with a hammer during the tightening process to encourage the bearing to slightly swivel in the housing and align with the shaft.

If a bearing flange or housing has a grease zerk, the accompanying bearing probably has a small hole or series of holes in its outer race to allow grease into its ball bearings. Before tightening the bearing flanges, 
rotate the bearing’s outer race to align one of those tiny holes with the base of the grease zerk in the bearing flange. 

Once a bearing is centered, aligned and its mounting bolts tightened, install its eccentric lock collar. Slide the collar against the bearing and rotate the collar in the same direction the bearing and shaft will turn during operation. Turn the lock collar by hand until it locks snug to the bearing, then use a hammer and punch to firmly tap it only twice in the direction of rotation.

Overtightening a lock collar can lead to premature  bearing failure. The design of the eccentric “ramps” on the faces of the lock collar and the bearing’s inner race quickly generate incredible clamping force as they rotate after initial contact. 

Hammering until the lock collar won’t rotate any further risks cracking the bearing’s inner race, which guarantees premature failure and probable shaft replacement in the near future. 

For what it’s worth, if a bearing “clicks” or a shaft makes an audibly faint “clunk” noise when rotated by hand, that’s symptomatic of a cracked inner bearing race caused by an overtightened lock collar. If the bearing is disassembled and its inner race has a half-moon-shaped crack or half-moon-shaped piece missing, the culprit is an overtightened lock collar. 


Cool Tool

Removing eccentric lock collars with a hammer and a punch requires three hands—one to hold the hammer, one to hold the punch and one to keep the lock collar/bearing/shaft from turning while you whack it. A tapered bit on an air hammer makes removal easy. Hold the lock collar with one hand, the air hammer with the other and pull the trigger. Price: $5 to $10 for a tapered bit.