Timken Single-Row Cylindrical Roller Bearings NU N NJ NUP ETP EJ EMA

Single-row cylindrical roller bearings for high radial loads and easy shaft expansion

Timken single-row cylindrical roller bearings carry heavy radial loads at moderate to high speed and, because one ring can slide axially on the rollers, they are used as the floating bearing that absorbs shaft growth. Timken lists them for helical and planetary gearboxes, geared motors, pumps, compressors, electric motors and centrifuges, in bore sizes from 15 mm to 1,200 mm across single-, double- and four-row designs.

Four cage families are offered in the single-row range: the ETP polymer cage for 15 to 80 mm bores (lightweight, low noise, high speed), the EJ stamped-steel cage for 65 to 150 mm bores, the EMA one-piece machined brass cage with proprietary profiles and textured surfaces, and full-complement NCF bearings that maximise the roller count for radial capacity.

Technical specifications

Sample catalogue values: dimensions d / D / B in mm, static C0 / dynamic C1 load rating in kN, thermal reference speed oil / grease in rpm:

Choosing the type, cage and clearance

Type NU (double-ribbed outer ring, straight inner ring) and type N (double-ribbed inner ring) suit the floating position because the free ring moves with minimum friction. NUP and NP, which have a loose rib, are considered the fixed bearing and are normally placed nearest the drive end of the shaft, with shaft end play set by the axial clearance in the fixed bearing. NJ and NF bearings can support light unidirectional thrust, and the sliding contact between rib and roller end makes lubrication critical near the limit.

Select ETP for compact high-speed pumps and gearboxes, EJ where a robust steel cage is wanted in the larger sizes and EMA where more demanding duty justifies the brass cage. In the sample table the EJ and EMA versions of the same size share load ratings but differ in mass. Specify radial internal clearance with the number, and for inch sizes note that the letter I in the number identifies inch bearings (RIU against metric RU).

What to confirm before ordering

Confirm the full designation, ring type (N, NU, NJ, NUP), cage suffix, clearance, shaft and housing fits, speed and lubrication. See Electric Motors, Pumps and Turbines for other Timken stock, and the 22216EJW33 spherical page for a related Timken roller bearing.

Mounting cylindrical roller bearings without damage

A practical advantage of the separable designs is that the inner ring and the outer ring with its roller set can be mounted separately. On an NU bearing, for example, the inner ring can be fitted to the shaft and the outer ring assembly pressed into the housing, then the two brought together during assembly of the machine. Bring them together carefully and with the parts aligned: pushing the roller set onto the inner ring at an angle can scratch the raceway and leave marks that later become the starting point of fatigue damage. Rotating the shaft slowly while sliding the parts together helps.

Where an interference fit is used, heat the inner ring evenly with an induction heater or in an oven instead of with a flame, and never pass mounting force through the rollers. Check shaft and housing seats for size, roundness and shoulder squareness before fitting, because the fit tables in the Timken catalogue assume correctly machined seats.

Start-up and lubrication checks

After assembly, turn the shaft by hand to confirm free rotation and, on a fixed-and-floating arrangement, check that the floating bearing can move axially as intended. Fill grease or establish oil flow according to the machine manufacturer's instructions, then run the machine at reduced load and watch bearing temperature and noise until they settle. A temperature that keeps rising, or a new noise, points to a fit, clearance, alignment or lubrication problem that should be found before full-load operation. For NJ and NF bearings carrying thrust, pay particular attention to lubrication, as the catalogue notes above.

Routine maintenance points

• Relubrication interval and quantity matched to speed, temperature and contamination at the machine.
• Trend vibration and temperature readings rather than relying on single measurements.
• Inspect seals and housing covers that keep contaminants out of the bearing.
• Keep spare bearings in their original packaging until fitting.

Bearings in Omani heat, dust and humidity

Gearboxes, pumps and motors in Oman and other GCC countries often run in high ambient temperatures, which raises the operating temperature of the bearing and shortens the life of the lubricant. Lubricant selection and relubrication intervals should therefore be reviewed for summer conditions, not only for the standard rating temperature. Fine sand and dust are a common cause of early bearing wear in desert and quarry sites, so housing seals, breathers and clean lubrication practice matter as much as the bearing itself. In humid coastal plants, moisture can enter housings as machines cool down after shutdown; stored bearings and idle machines benefit from protection against corrosion. When ordering replacements, quote the full designation including the cage suffix and clearance so that the new bearing matches the original duty.

Documents and quotation

The attached Timken Cylindrical Roller Bearing Catalog (130 pages) holds the single-row, two-row and four-row product tables, fits, clearances and cage notes. Send the designation and quantity when requesting a quotation from Seven Star LLC, an independent supplier in Muscat.