Outline the significance of journal bearings in the oil system and how wear is assessed during overhaul.

• A. They store fuel and oxygen.
• B. They act as heat exchangers in the exhaust system.
• C. They control airflow in the compressor stage.
• D. Provide rotor support with an oil film; wear assessed by bore measurements, surface finish checks, play/endplay, and oil clearance per OEM.

Answer: (D)

Journal bearings support the rotor by forming a thin oil film that carries the loads and keeps the shaft centered. In the oil system, this film provides hydrodynamic lubrication, reducing friction and wear while allowing smooth rotation. Over time, wearing of the bearing journal or bearing surface, or an increase in clearance, alters the film thickness and rotor alignment, which can lead to rubbing, overheating, and reduced efficiency.

During overhaul, wear is checked by measuring how much the bearing bore and the journal have worn, inspecting the bearing surfaces for scoring or pitting, and assessing the rotor’s clearance and movement. The bore and journal sizes are measured with precision instruments to determine wear and dimensional changes; surface finish is checked to ensure the surfaces remain smooth and free from damage; the rotor’s play (radial and axial) is measured to detect excessive endplay or misalignment; and oil clearance is verified against OEM specifications, since the correct film thickness depends on those limits. If the measurements fall outside the approved limits, bearings are replaced or reworked to restore proper oil film behavior and rotor alignment.