http://www.engineparts.com/products/bearingtech_files/frame.htm
includes many failure pictures and diagnostic symptoms. here are a few excerpts i found most interesting
[B]MAJOR CAUSES OF PREMATURE BEARING FAILURE
DIRT 44.9%
13.4% Misassembly
12.7% Misalignment
10.8% Insufficient Lubrication
9.5% Overloading
4.2% Corrosion
4.5% All Other Causes
Foreign Particles
Metallic -Wear -Machining
Abrasive -Honing -Grinding -Polishing -Airborne -Air Ingested
Blasting Media -Glass Beads -Steel Shot
Carbon
Lubricant - Deterioration
Crush
Each half shell is about .005” more than a half circle. As the bolts are tightened, the bearings are compressed like springs. The resulting force holds the bearings tight. Lugs on the bearings are only locators to insure proper installation
[/B]