it indicates that the bearing has failed

 needle roller bearings operating under conditions such as high speed, and high operating temperatures, special attention should be rotating rings can not be too loose to prevent eccentric, as well as non-fixed ferrule with a gap to prevent sleeve ring deformation under load and to stimulate vibrations.
Rolling in the work allow slight noise, if the noise is too large or unusual noise or crash, it indicates that the Bearing test machine has failed.
Preload is the bearing assembly to the inner or outer ring an axial force to remove the needle bearing clearance, and to move the body and the inner and outer contacts generated at the beginning of deformation. Preload can improve the working condition of the bearing stiffness and rotational accuracy, load bearing large, rotating high precision bearings, mostly in the absence of even a small amount of clearance over the work of state interference, in which case it required in the assembly, the bearing preload. Clearance and preload adjustment are usually seen by the inner ring relative axial displacement of appropriate methods to complete. From the above process is not difficult to learn concepts, through to move the bearing clearance adjustment, can improve the bearing capacity and rotation accuracy, progressive bearing life. But at the same time make the bearing frictions, fever increases, so the clearance or preload adjustment when necessary to ensure good lubrication and heat dissipation. If improperly adjusted or poor lubrication, it will in turn cause increased bearing wear, reduced life expectancy.