NA357 357S

Common issues

• Bearing wear (thrust and journal plain bearings) leading to increased rotor clearances and vibration.
• Compressor fouling due to intake air quality, oil carry-over from engine or turbocharger seals, reducing efficiency and air flow.
• Turbine fouling and/or erosion due to exhaust gas quality (e.g., high sulfur fuels, unburnt fuel particles), affecting turbine efficiency and potentially causing blade damage.
• Oil leakage from bearing housing seals (labyrinth or piston ring type) leading to oil consumption and potential contamination of compressor/turbine sides.
• Rotor imbalance and excessive vibration due to fouling, blade damage, or bearing wear, potentially leading to catastrophic failure.
• Nozzle ring distortion, cracking, or erosion, impacting turbine performance and exhaust gas flow.
• Diffuser damage or fouling, affecting compressor efficiency and air delivery.
• Turbocharger surging, often related to engine load changes, fouling, or issues with engine control systems.

Inspection checklist

• Check for any visible oil leaks from bearing casing drains, seals, and lubrication oil connections.
• Monitor and trend bearing temperatures (if sensors fitted) and lubrication oil pressure/flow to the turbocharger.
• Visually inspect compressor impeller for fouling, erosion, or foreign object damage (FOD) through the air intake.
• Visually inspect turbine blades and nozzle ring for fouling, erosion, cracks, or signs of impact damage through exhaust gas ports/inspection covers.
• Check rotor axial and radial clearances (if accessible via inspection ports or during planned maintenance) against manufacturer's limits.
• Listen for abnormal noises (e.g., whining, rubbing, grinding) and feel for excessive vibration during engine operation.
• Inspect the condition of the air filter elements (if external to the turbocharger) and ensure proper air intake.
• Verify the proper functioning and cleanliness of compressor and turbine wash systems (nozzles, drains).
• Check the security of all mounting bolts, exhaust gas, and air duct connections.

Service intervals

Typical wear limits

Ranges are typical for this design class. Always confirm against the manufacturer documentation for your serial number.

Critical spares

• Complete bearing cartridge assembly (journal and thrust bearings, often supplied as a single unit for plain bearing designs).
• Oil sealing rings / labyrinth seals (for both compressor and turbine sides).
• Full set of O-rings and gaskets for common access covers and connections.
• Compressor wash nozzles.
• Nozzle ring segments (if modular design).
• Diffuser segments.
• Lube oil filter elements (if integral to the turbocharger lubrication system).

Safety

• Extremely high surface temperatures of exhaust gas casing and turbine components (severe burn hazard).
• High rotational speeds of the rotor (risk of catastrophic failure if imbalance or bearing failure occurs, leading to flying debris).
• Pressurized air and exhaust gas systems (potential for blow-outs if covers or connections are improperly secured during maintenance).
• Hot lubrication oil under pressure in the bearing system.
• Risk of inhaling exhaust gases or cleaning chemicals during maintenance procedures.

Class survey

Class surveyors typically check for overall external condition, absence of oil/exhaust gas leaks, and general cleanliness. They will review maintenance records, including running hours, bearing temperature trends, and records of compressor/turbine washing. During special surveys (e.g., 2nd or 3rd), an internal inspection of the compressor and turbine sides may be required, especially if performance issues or high running hours are noted. Verification of mounting security and the presence of critical spare parts are also common checks. Functionality of safety devices (e.g., overspeed trip, if fitted) and compliance with manufacturer's maintenance guidelines are also assessed.

Estimated lifetime: 16,000 - 24,000 hours (interval for major overhaul before significant component replacement or reconditioning is typically required)