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 — cone number in the L521900 inch series; sets the 4.250 in bore.L521910D — cup number with a trailing D for double cup. This is the giveaway that the assembly is two-row: a single wide outer ring carrying two opposed raceways, in place of two separate cups.TDO — Timken’s designation for the resulting arrangement. The two rows sit back-to-back within the double cup, which is what gives the assembly its wide effective bearing spread.

Why TDO and not two single-row bearings

This is the question that decides whether the part is right for you. 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.

The trade is that a back-to-back pair has its load lines diverging outward, so the effective spread is wide and the moment stiffness is high — excellent for 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 is what makes it convenient for expansion positions in long shaft systems.

Published ratings and mounting data

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 — use the two-row values when sizing a TDO.

Bore (d): 4.2500 in / 107.95 mmCup outside diameter (D): 5.7500 in / 146.050 mmCone width (B), each: 0.8438 in / 21.433 mmSingle cup width (C), for reference: 0.6563 in / 16.67 mmDynamic radial load rating C1, single row: 20,000 lbf / 88,900 NDynamic radial load rating C90, single row: 5,180 lbf / 23,100 NDynamic axial rating Ca90, single row: 3,480 lbf / 15,500 NStatic radial load rating C0, single row: 39,400 lbf / 175,000 Ne factor 0.39, K factor 1.49, Y factor 1.53Shaft backing shoulder diameter (da): 4.49 in / 114 mm; (db): 4.57 in / 116 mmHousing backing shoulder diameter (Da): 5.57 in / 141.00 mm; (Db): 5.35 in / 135.89 mmMaximum shaft fillet radius cleared: 0.06 in / 1.5 mm; maximum housing fillet: 0.06 in / 1.52 mm

The overall assembly width across the two cone backfaces and the two-row C1 and C90(2) ratings are not published on the source consulted for this part, so they are deliberately left out rather than estimated. Distributor listings quote the double-cup width for this assembly as 1.9375 in; that figure is a distributor value, not a manufacturer one, and is offered here as an indication only.

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 genuine combined-load bearing rather than a radial-only one, which is exactly why it is offered in a two-row double-cup form — the arrangement exists to exploit thrust capacity in both directions. 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 comes into play.

Fitting notes

Setting a TDO is different from setting two single-row bearings, and getting it wrong is the usual cause of early failure. The internal endplay of a TDO assembly is built in at the factory by grinding the cone backfaces to a controlled stack height — the two cones are clamped solidly together on the shaft and the resulting clearance is whatever the assembly was ground for. You do not shim it, and you must not mix cones between assemblies, because doing so destroys the ground endplay.

Clamp the cones firmly against each other and against the shaft shoulder. Respect the 0.06 in maximum shaft and housing fillet radii. Drive the double cup into the housing square, bearing on the cup face and never on a raceway.

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, forty pieces, if you only need to replace a cone and your double cup is still serviceable.