Timken78215/78551Single-Row Tapered Roller Bearing, Cone and Cup, 2-1/8 in Bore x 5.513 in OD

Product Description

What this part is

A Timken 78215/78551 single-row tapered roller bearing, supplied as both halves together: the 78215 cone with its rollers and cage, and the 78551 cup. Bore 2-1/8 in, outside diameter 5.513 in.

Quantity and configuration

1 Set — one cone and one matching cup, which is one complete bearing.

Decoding the designation

Timken writes a tapered roller bearing as cone number over cup number. 78215 is the cone and fixes the bore, the cone width and the raceway angle. 78551 is the cup and fixes the outside diameter and the matching outer raceway. Either half can be ordered on its own by its own number.

Brand marking

The bearing is marked Timken/Bower. Bower was a long-established American tapered roller bearing maker whose line came into Timken, and the Bower name continued on cartons and rings after that. It identifies the same part rather than a different one.

What these specs mean in practice

A 2-1/8 in bore inside a 5.513 in outside diameter is a heavy section for the shaft size, giving long rollers and a large raceway contact for the bore — the proportion used where load is high and speed moderate, such as pinion heads, mill drives and heavy wheel ends. Tapered roller geometry takes that radial load together with substantial thrust in one direction, so the type is fitted in pairs facing opposite ways to hold the shaft both ways.

Condition

New old stock with surface staining from storage. The raceways, rollers and ground faces are unused.

Fitting notes

Cup and cone are pressed home separately, each with force on its own back face and never through the rollers. Once both are seated, the bearing is set by moving one race axially against the other to establish the intended end play or preload, since a tapered roller bearing carries no built-in clearance.

Interchange guidance

78215 and 78551 are industry-standard numbers, so a cone marked 78215 and a cup marked 78551 from another tapered roller bearing maker interchange as the same specification. The 78250 and 78255 are different cones in the same family and are related sizes rather than substitutions.