Cylindrical roller bearings have rollers instead of balls as the rolling elements. Because the roller is a cylinder, the contact between roller and raceways is a line instead of a point as in the case of ball bearings. Because of this greater contact area the radial load carried by the bearing is spread over a larger area enabling the bearing to handle much greater radial loads for longer periods than a ball bearing of the same boundary dimensions.

Cylindrical roller bearings are commonly used in medium- and large-sized electric motors when high forces are present at the drive-end of the shaft, for example by belt pull, coupling misalignment or gear forces created by the assembly which the motor is driving. They are usually fitted to the drive-end of the shaft and by their construction permit axial displacement of the inner ring relative to the outer ring due, usually, to thermal expansion of the shaft when the motor reaches operating temperature. A deep groove ball bearing is normally fitted to the other, non-drive end of the shaft principally to retain the shaft in the motor but also to locate the commutator in the correct position relative to the carbon brushes and the rotor in the correct position relative to the stator.

These bearings are separable and are produced in several designs. Bearings of N and NU design have one double flanged ring carrying the roller and cage assembly while the other ring has no flanges, allowing free axial displacement relative to the other ring. Bearings of this design can not accommodate axial loads. Bearings of NJ design have one double flanged outer ring carrying the roller and cage assembly, the inner ring has one flange that can accommodate light axial loads in one direction. These are routinely used in vibratory and traction motors.

Most of cylindrical roller bearings for electric motors are designed to fit into one or three series of standard dimensions for the bore and outside diameter. The following figure demonstrates the increase or decrease in load carrying capacity in relation to the proportions of the bearing bore. The width dimension may vary depending on the application or requirements for sealing devices, extra radial load capacity and extra grease reservoir.

Duty Ratings:

200 series – Light duty
300 series – Medium duty
2300 series – Heavy duty

Cylindrical roller bearings are available with pressed steel or machined brass cages,centered either on the rollers or outer ring. Small and medium-sized bearings have a window-type steel cage as standard, larger bearings have a brass cage as standard. The explanation of the different designation suffixes is as follows:

E : steel cage with increased loading capacity
M : brass cage guided on the rollers
EM : brass cage guided on the rollers with increased loading capacity
EMA : brass cage guided on the outer ring with increased loading capacity