(republished on 07/13/06)
Except for extremely loose bearings, bearing adjustment is normally not an issue in terms of machine function or energy loss. Bearing adjustment does have a significant impact on bearing life. Usually bearing life is maximized for rolling element bearings like ball and roller bearings when they are lightly preloaded, however, bearing life is usually not significantly reduced for installations with zero clearance (zero preload) or even for slight clearance. In most modern machines, the bearing mountings are manufactured such that adjustment of the bearings is not possible. An exception to this rule is the case of tapered roller bearings (often used as automotive wheel bearings). The issues are discussed on page A140 of the Timken Products Catalog (Engineering) available at http://www.timken.com/en-us/products/Pages/TimkenProductsCatalog.aspx. Unfortunately, the optimal setting is difficult to specify without careful testing. Frequently, the cold bearing setting, either a preload or endplay, will change significantly when the machine reaches operating temperature. This makes it impossible to specify a general rule of thumb. However, it is best to err on the side of excess endplay because excessive preload can cause drastically shortened bearing life and in the extreme can produce deformation of the bearing races (brinelling, see http://www.answers.com/topic/brinelling).
(published on 11/15/11)