TimkenL521948/L521910DDouble-Row TDO Tapered Roller Bearing Assembly, 4.250 in Bore x 5.750 in OD, Two Cones in One Double Cup

Product Description

What this part is

This is a two-row tapered roller bearing in Timken’s TDO configuration, Tapered Double Outer. It consists of two L521948 cone assemblies (inner rings with rollers and cages) running in a single wide L521910D double cup. Bore is 4.250 in (107.95 mm), cup outside diameter is 5.750 in (146.050 mm), from the L521900 inch series.

Decoding the designation

L521948 is the cone number in the L521900 inch series and sets the 4.250 in bore. L521910D is the cup number, with a trailing D for double cup: a single wide outer ring carrying two opposed raceways in place of two separate cups. TDO is Timken’s designation for the resulting arrangement, with the two rows sitting back-to-back within the double cup, giving the assembly its wide effective bearing spread.

Why TDO and not two single-row bearings

A TDO does three things a single-row tapered bearing cannot. It takes thrust in both directions, so it locates a shaft axially without a second bearing opposing it. It resists overturning moment, because the two rows are separated by the width of the double cup and react a tilting couple between them. And it does both from one housing bore with one shoulder, which collapses the machining and the assembly stack-up into a single fit.

A back-to-back pair has its load lines diverging outward, so the effective spread is wide and the moment stiffness is high, which suits a short overhung shaft, a wheel end, a crane sheave or a gearbox output taking a belt pull. Timken notes the TDO can be used in a fixed position or allowed to float in the housing bore, which makes it convenient for expansion positions in long shaft systems.

Published ratings

Single-row data below is Timken’s published figures for the L521949 / L521910 assembly, which shares this bearing’s bore, section and internal geometry. The two-row assembly does not simply double the single-row rating.

Bore (d): 4.2500 in / 107.95 mm. Cup outside diameter (D): 5.7500 in / 146.050 mm. Cone width (B), each: 0.8438 in / 21.433 mm. Single cup width (C), for reference: 0.6563 in / 16.67 mm. Dynamic radial load rating C1, single row: 20,000 lbf / 88,900 N. Dynamic radial load rating C90, single row: 5,180 lbf / 23,100 N. Dynamic axial rating Ca90, single row: 3,480 lbf / 15,500 N. Static radial load rating C0, single row: 39,400 lbf / 175,000 N. e factor 0.39, K factor 1.49, Y factor 1.53. Double-cup width, distributor-quoted: 1.9375 in.

What these specs mean in practice

The K factor of 1.49 sets the cup angle and therefore the balance of radial to axial capability. At 1.49 this series is a combined-load bearing rather than a radial-only one, which is why it is offered in a two-row double-cup form. The e factor of 0.39 is the axial-to-radial load ratio at which the equivalent-load equation changes; below it thrust is ignored in the calculation, above it the Y factor of 1.53 applies.

Mounting data

Shaft backing shoulder diameter (da): 4.49 in / 114 mm; (db): 4.57 in / 116 mm. Housing backing shoulder diameter (Da): 5.57 in / 141.00 mm; (Db): 5.35 in / 135.89 mm. Maximum shaft fillet radius cleared: 0.06 in / 1.5 mm. Maximum housing fillet: 0.06 in / 1.52 mm. Effective centre location, single row: +0.19 in / 4.8 mm.

The internal endplay of a TDO assembly is built in at the factory by grinding the cone backfaces to a controlled stack height, and the resulting clearance is whatever the assembly was ground for.

Interchange guidance

These are industry-standard inch designations. Cross-references: L521948/L521910D, L521948-L521910D, L 521948 / L 521910D. Sibling cone with the same bore: L521949, giving the L521949/L521910D assembly. Related single-row assemblies from the same series: L521949/L521910, L521949/L521914. Component numbers: cone L521948, double cup L521910D.

Central Surplus also stocks the L521948 cone on its own under SKU BAY3#3VA4EO.