Description

1. TASK 72-43-00-990-501 Description and Operation of the No. 4 Bearing and Rear Compartment

   1. Description

      1. The primary parts of the No. 4 bearing and rear compartment assembly, refer to Figure, are:

         1. No. 4 Bearing

         2. No. 4 Bearing Seal Spacer

         3. No. 4 Bearing Front and Rear Seal Seats

         4. Rear Bearing Compartment

         5. No. 4 Bearing Rear Seal Assembly

      2. The related parts of the No. 4 Bearing Front Compartment are:

         1. No. 4 Bearing Support Assembly

         2. No. 4 Bearing Front Compartment

         3. No. 4 Bearing Front Seal Assembly

      3. The No. 4 bearing and rear compartment, when assembled with the No. 4 bearing front compartment, completes the assembly of the No. 4 bearing within an insulated and sealed area.

      4. The No. 4 bearing is a cylindrical roller bearing. The inner race has shoulders which guide the rollers in the race. The outer race, installed in the No. 4 bearing support assembly, is machined elliptical so that the bearing rollers cannot skid. The outer race is held in the No. 4 bearing support assembly by a nut and key washer.

      5. The front and rear bearing compartments are made of three separate walls. The walls form insulation chambers. The inner wall of each compartment forms a chamber with the middle wall, and carries cool air around the bearing area.

      6. Oil for lubrication of the No. 4 bearing and the front and rear seals is supplied through a diffuser case internal tube which is attached to the No. 4 bearing front compartment.

   2. Operation

      1. Cool air comes from the HP compressor, and is carried into the No. 4 bearing front compartment through three diffuser case internal tubes. The outer wall of each bearing compartment, separated from the middle wall by an air space, forms a heatshield around each bearing compartment.

         The cool air, carried to the No. 4 bearing front and rear compartment, also causes higher pressure in the compartment to keep out hot combustion chamber gases.

      2. Passages in the compartment send oil into the bearing compartment. The oil is then sent to the No. 4 bearing and the carbon seal faces. Scavenge oil is carried away through another diffuser case internal tube.

      3. The front and rear seal seats have oil-wetted surfaces for the front and rear carbon seals to seat against. The seal assemblies make a low-friction seal against the rotating seal seats. The seal effect is maintained by the pressure differential and the spring-loaded carbon seals.

      4. The bearing forces are carried to the diffuser case through the No. 4 bearing support assembly.

      5. The No. 4 bearing seal spacer holds the bearing in the correct axial location when installed on the HPC drive shaft.

      6. In this way, the No. 4 bearing is provided with lubrication, support and protection from high temperatures.

   3. Module Sub-Assemblies

      Listed below is the breakdown of sub-assemblies within the module:

      SNS		Part
      Location		No. 4 Bearing And Rear Compartment Assembly Nomenclature
      72-43-11		No. 4 bearing front seal seat
      72-43-12		No. 4 bearing seal spacer
      72-43-13		No. 4 bearing
      72-43-14		No. 4 bearing rear seal seat
      72-43-20		No. 4 bearing rear seal assembly
      72-43-30		No. 4 bearing rear cooling duct and heatshield

Figure: No. 4 bearing and rear compartment

No. 4 bearing and rear compartment