NSK6028CMOpen Single-Row Deep Groove Ball Bearing 140x210x33 mm, CM Electric-Motor Clearance, Pressed Steel Cage

Product Description

What this part is

A single-row deep groove ball bearing in the 60-series, 140 mm bore, 210 mm outside diameter, 33 mm wide. It is an open bearing — no shields and no seals — so it carries radial load and moderate axial load in either direction, and it relies on the housing for sealing and on the machine for lubrication.

Decoding the designation

6028 — ISO 60-series single-row deep groove ball bearing, 140 x 210 x 33 mm.Open — no suffix for closure means no shield and no seal. NSK uses Z / ZZ for metal shields and D, DU, DDU, V, VV for rubber seals; none of those appear here.CM — NSK’s non-interchangeable radial internal clearance specified for electric motor applications. It is a narrowed clearance band, not simply a wider or tighter grade.Pressed steel cage, the standard cage for this designation.

What these specs mean in practice

CM clearance is the reason to buy this part rather than a plain 6028. Electric motors run with an interference fit on the shaft and a warm inner ring, both of which eat radial clearance. CM is toleranced to leave the right operating clearance once the motor is hot, which is what keeps noise and vibration down and stops the balls from skidding. Fit a normal-clearance bearing where CM was specified and you can end up preloaded when warm; fit a C3 and you may get an audibly noisier machine and more ball skid at light load. It matters in both directions.

Because the bearing is open, it arrives without a lubricant charge held in place by a closure. Grease or oil it on assembly and make sure the housing seal is doing its job — an open bearing is not a substitute for a sealed one, and a sealed 6028DDU or shielded 6028ZZ is not a drop-in here either, since those bring their own grease and different width tolerances on the closure faces.

Published ratings and mounting data

Bore: 140 mmOutside diameter: 210 mmWidth: 33 mmBasic dynamic load rating Cr: 121,000 NBasic static load rating C0r: 109,000 NLimiting speed, grease lubrication: 2,800 rpmLimiting speed, oil bath: 3,400 rpmNumber of balls: 16Ball diameter: 20.638 mmChamfer r (min.): 2 mmShaft abutment diameter da: 149 mm min, 158.5 mm maxHousing abutment diameter Da (max.): 201 mmFillet radius ra (max.): 2 mmCalculation factor fo: 16Mass: approximately 3.48 kg

Quantity and configuration

This listing is for 1 Pc — one single-row bearing, supplied on its own. It is not a matched pair and needs no mating half.

Fitting notes

Respect the abutment diameters above so the shoulder clears the seating face and does not bear on the ring corner. Heat the bearing or use a hydraulic fit for the inner ring rather than driving it through the balls. Check that the shaft and housing tolerances match the clearance grade you are working to — a CM bearing on an oversize shaft loses the benefit of the narrowed band immediately.

Interchange guidance

Direct interchanges are other manufacturers’ open 6028 with equivalent electric-motor clearance. SKF 6028, FAG 6028, NTN 6028 and Koyo 6028 share the 140 x 210 x 33 mm envelope; match the clearance code before treating any of them as equivalent, because plain CN, C3 and C4 versions are related sizes rather than substitutes for CM. NSK 6028ZZ (shields), 6028DDU (rubber seals), 6028C3 and 6028C4 all share the same envelope but differ in closure or clearance and should be treated as related sizes, not equivalents.