GE LM2500 Bearing System Technical Reference

Bearing Locations & Operating Roles

Bearing	Location	Function
3R	Compressor Rear (A-Sump)	Radial support for the rear of the High Pressure Compressor (HPC).
4R / 4B	TBE (B-Sump)	4R: Radial support for the High Pressure Turbine (HPT). 4B: Thrust bearing for the HPT rotor.
5R / 6R	TBE (B-Sump)	Radial support for the aft end of the HPT rotor.
7B / 7R	PT Front (D-Sump) PT Rear (D-Sump)	Radial support for the Power Turbine (PT) rotor inlet. 7B: Main thrust bearing for the PT. 7R: Final radial support at the output shaft.

Technical Specifications & Operating Conditions

Feature	Specification
Rotational Speed	Ng (GG): ~9,500–10,000 RPM
Lubrication	Under-race cooling and side-jet spray (MIL-PRF-23699)
Max Temperature	Stabilized oil discharge temp up to 300°F (149°C)
Sump Environment	Pressurized by 8

Materials & Coatings

Races & Rolling Elements: M50 Tool Steel
Chosen for its high ‘Hot Hardness’ (>58 HRC at operating temps).

Cages (Retainers): Silver-plated AMS 4616 (Silicon Bronze) or High-strength Steel
The silver plating acts as a sacrificial solid lubricant to prevent galling during transient cycles.

Coatings:

	Feature	What to Look For
Black Oxide	Applied to races	Improve oil retention and prevent “standstill” corrosion.
Tungsten Carbide	Outer diameter of race (housing intePrfarecvee)nt fretting at the housing interface.

Part Numbers (Reference Only)

Bearing	Typical Part Number
#3	1959M19P01
#4	1959M21P01 (Matched Set)
#5	1959M23P01
#6	1959M24P01
#7	1959M26P01

Failure Modes & Symptoms

Quick Decision Checklist

Before finalizing your choice, run through this:

Bearing Group	Typical Lifespan	Notes
GG Bearings (3R, 4R, 4B, 5R)	25,000 to 35,000 hours	Higher speeds and temperatures reduce service life.
PT Bearings (6R, 7B, 7R)	50,000+ hours	Lower speeds and cleaner environment extend lifespan.

This document is for technical reference purposes. Always consult official GE Aviation maintenance
manuals and engineering documentation for operational procedures.