Proper Tapered Roller Bearing Installation in the Hub Assembly
The proper adjustment of the two bearings in the hub assembly is one of the most important aspects of the installation process.
Excessive tightening of the adjustment nut, otherwise known as excessive preload, can cause the type of rapid deep spalling shown in these pictures. This deep spalling occurs when the direct contact between rollers and raceway caused by excessive preload super heats the bearing, softening the material, and allowing chunks to be torn away from the raceway and rollers during operation.
On the other side of the spectrum, loosening the adjustment nut too much will cause excessive end play in the bearings, allowing a rocking motion that disrupts the even distribution of force along the rollers. This, too, can cause bearing failure resulting in damage similar to that in this picture. As you can see, the damage is restricted to one section of the raceway that underwent extreme stress due to excessive end play.
The key then is to hit the sweet spot between too much end play and not enough. For Timken bearings, this means achieving an end play between .001 inches and .005 inches. To help, Timken has established an easily measurable three step adjustment procedure.
While rotating the rotor to ensure roper seating of the rollers, induce preload by using a torque wrench to tighten the adjusting nut to 50 foot pounds. Then loosen the adjusting nut one full turn. While continuing to rotate this rotor, re-torque the nut, this time to 10 foot pounds. Once again, loosen the adjusting nut, this time by only 1/6 to 1/4 turn. When step one is complete, place the bottle cap type stamping over the adjusting nut and properly install and secure the cotter pin to prevent the nut from backing off.
Use a dial indicator to measure end play. Mount the indicator’s base as close to the center of the hub rotor as possible. With the indicator tip against the end of the spindle, set the indicator to zero. Grasp the rotor at 3 o’clock and 9 o’clock and begin oscillating the rotor back and forth. While oscillating, push the rotor in and read the dial indicator. Then pull the rotor while still oscillating and read the dial indicator again. The bearing end play is equal to the total indicator movement, which should be between .001 and .005 inches.
If you have not achieved the desired end play, repeat steps one and two.
Once you achieve the desired end play, the adjustment process is complete. When properly done, this simple step by step adjustment process increases the life span of your bearings and significantly reduces the chance of damage.