TimkenNA78250Tapered Roller Bearing Cone 2-1/2″ Bore, Inch Series, TDO Two-Row Component, Cone Only

Product Description

What this part is
A Timken NA78250 single-row tapered roller bearing cone: the inner ring with its tapered rollers and cage retained as one unit. Inch (imperial) series, 2.5000 in bore. Cone only. The matching double cup is the Timken 78549D, which takes two of these cones.

Designation breakdown
78250 is the cone number. The NA prefix marks a cone furnished as a component of a two-row matched assembly rather than as one half of a standalone single-row bearing. 78549D is the cup number, and the D suffix on that cup identifies it as a double cup, one outer ring with two raceways. Written 78250/78549D, the pair describes a TDO assembly: Tapered Double Outer, two cone rows back to back inside a single cup.

Specifications
Manufacturer: The Timken Company. Part Number: NA78250. Base Number: 78250. Cone Part Number: 78250. Cup Part Number: 78549D. Bearing Type: tapered roller bearing cone, single row, inch, TDO component. Series: 78000. Bore (d): 2.5000 in / 63.500 mm. Cone Width (B): 1.3085 in / 33.236 mm. Raceways On This Ring: 1. Rolling Elements: tapered rollers. Cage Type: stamped one-piece roller cage. Cage Material: stamped steel. Bearing Material: case-carburized alloy steel. Closure Type: open. Mounting Arrangement: TDO, Tapered Double Outer, two cone rows back to back in one double cup. Cone Backface To Clear Radius (R): 0.09 in / 2.300 mm. Cone Backface Backing Diameter (db): 3.35 in / 85 mm. Cage-Cone Backface Clearance (Aa): 0.24 in / 6.1 mm. Design Units: inch (imperial). Harmonization Code: 8482.20.00. Country of Origin: United States.

Assembly data, 78250 cones with the 78549D double cup
These figures are published by Timken for the complete two-row 78250/78549D assembly, not for a single cone. Cup Outside Diameter (D): 5.5000 in / 139.700 mm. Double Cup Width (C): 2.0395 in / 51.803 mm. Bearing Width Across Cones (T): 3.0625 in / 77.788 mm. Cup Backface To Clear Radius (r): 0.06 in / 1.5 mm. Cup Frontface Backing Diameter (Da): 5.19 in / 131.83 mm. Effective Center Location (a): 0.31 in / 7.9 mm. Dynamic Radial Rating, one row, 90M revs (C90): 11,800 lbf / 52,600 N. Dynamic Radial Rating, two row, 1M revs (C1): 79,300 lbf / 353,000 N. Dynamic Radial Rating, two row, 90M revs (C90(2)): 20,600 lbf / 91,500 N. Dynamic Thrust Rating, 90M revs (Ca90): 17,500 lbf / 77,900 N. K Factor: 0.67. e Factor: 0.87. Y1: 0.78. Y2: 1.16. Geometry Factor (Cg): 0.0884. Related Timken assembly numbers: 78250-90022, 78250-90023, 78250-90024, 78250-90061, 78250-90085, 78250-90095, 78250-902A2.

What these specifications mean in practice
Two cone rows seated back to back in one double cup carry thrust in both directions and give a wide effective bearing spread, which resists overturning moment from a short shaft section. That spread is why the arrangement appears in wheel hubs, crane sheaves and roll necks. TDO bearings run in fixed positions or float in the housing bore. As a single cone, this part is one of the two inner rings in that assembly.

Set composition
One cone assembly: inner ring, rollers and cage. The double cup and any spacer are separate components, and a complete TDO uses two cones.

Interchange
78250 is the industry cone number and carries unchanged across the inch tapered interchange. Cones 78214, 78215C and 78255X also run against the 78549D double cup, each at a different bore. A cone with no NA prefix carries the same raceway geometry.