Dan Anderson: How to Replace Bearings

February 25, 2019 09:59 AM
According to bearing manufacturers, attention to detail during installation is key to maximize the performance and longevity of replacement bearings.

According to bearing manufacturers, attention to detail during installation is key to maximize the performance and longevity of replacement bearings.

When installing a bearing that uses two bolt-together sheet metal flanges to hold the bearing in place, lift, wiggle, tap with a hammer or preferably rotate the shaft as you tighten the nuts that hold the flanges in place.

The wiggling, tapping and rotating help shift the bearing inside the flanges and align it with the shaft as the nuts are tightened, before the lock collar is installed. If the bearing is misaligned with the shaft when the lock collar is installed, the misalignment might cause: (1) the shaft to turn with a “tight spot” rather than freely rotate, which can cause premature failure, or (2) create so much shear stress to the inner race of the bearing that its lock collar ring cracks and allows the bearing to spin on the shaft.

Don’t over-tighten lock collars. A few firm taps with a hammer and punch are enough to lock the bearing to the shaft. The eccentric ramps on the bearing and lock collar develop incredible force as they lock together. Banging away with a hammer and punching until the hole in the lock collar is mangled can crack the bearing’s inner race.

When installing a pillow block bearing, where the bearing is part of a pre-assembled cast iron housing, slide the bearing and housing onto the shaft until the housing is against where it will be bolted. Install the bearing block’s bolts and snug them finger-tight while lifting or rotating the shaft and tapping the bearing block with a hammer. Again, the goal is to get the bearing to align with the shaft.

Install the lock collar on pillow block bearings with a few light taps, then spin the bearing and shaft by hand. Any stiff spots or resistance to free rotation indicates the bearing, bearing block and/or the lock collar are out of alignment. If the shaft has a load on it, to the point it can’t be easily spun by hand, run the machine. A misaligned bearing assembly will build heat more quickly than nearby bearings and might also add a new vibration to the machine’s normal vibrations.

In the rush to assemble greaseable bearings during field repairs it’s easy to misalign grease zerks with their grease holes or channels. Grease holes in the outer bearing race will allow applied grease to reach the bearing’s balls or rollers—but only if the grease can get to that little hole.

There’s enough clearance between the flanges and outer bearing race so grease can theoretically be pumped to the grease hole no matter where it is on the outer circumference of the bearing. Aligning the grease hole beneath the grease zerk ensures grease gets where it’s supposed to go.

When greasing bearings, lubrication and bearing engineers emphasize over-greasing can be as harmful as under-greasing.

Grease not only lubricates bearings, but helps cool them. Bearings are designed so the rotation of the bearing constantly moves grease within the bearing, transferring grease from motion-warmed areas to cooler areas and vice versa. Pumping a bearing too full with grease can actually inhibit the movement of grease within the bearing and cause it to run warmer than designed.

Finally, if a bearing frequently fails despite careful installation and proper lubrication, associated belts, chains or drives might be overloading that bearing. If the bearing seems to be the consistent point of failure, consider upgrading to a higher quality bearing. All bearings are not created equal.

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