NA357

Common issues

• Compressor-side fouling (due to dirty intake air or oil carry-over)
• Turbine-side deposits (from poor fuel combustion or exhaust gas quality)
• Bearing wear (journal and thrust bearings, leading to increased clearances and vibration)
• Rotor vibration (imbalance due to fouling, damage, or bearing wear)
• Oil leakage (from bearing housings, often indicating worn seals or excessive pressure)
• Exhaust gas leakage (from casing joints, expansion bellows, or drain lines)
• Air filter clogging (restricting airflow, leading to reduced engine performance and surging)

Inspection checklist

• Visual inspection of compressor impeller and turbine wheel for damage, erosion, or heavy fouling.
• Check axial and radial bearing clearances (using a dial gauge) against manufacturer's limits.
• Inspect bearing housing for oil leaks and ensure oil drain lines are clear.
• Check exhaust gas casing and connections for signs of leakage (soot stains, hot spots).
• Inspect air intake filter elements for cleanliness and integrity.
• Verify security of mounting bolts and anti-vibration mounts.
• Check rotor free rotation by hand (when cold and safe to do so) for smoothness and absence of rubbing.
• Inspect cooling water connections (if applicable) for leaks and proper flow.
• Monitor turbocharger performance parameters (boost pressure, exhaust gas temperatures pre/post turbine, speed) for deviations.

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 cartridges (journal and thrust bearings)
• Oil seals and O-ring kits
• Gasket sets for casing joints and connections
• Air filter elements
• Impeller nut and locking washer
• Special tools for disassembly/assembly (e.g., rotor locking tool, bearing pullers)
• Nozzle ring segments (if applicable, though NA series often have fixed geometry)

Safety

• High surface temperatures (exhaust casing, turbine housing) – risk of burns. Ensure insulation is intact.
• High-speed rotating machinery – risk of injury from contact or uncontained failure. Always ensure rotor is stopped and locked before inspection/maintenance.
• High-pressure air and exhaust gases – ensure all connections are secure before operation.
• Noise levels – can exceed safe limits, require hearing protection in vicinity.
• Potential for uncontained blade liberation in case of catastrophic failure – ensure safety barriers/shielding are maintained.

Class survey

During annual class surveys, the surveyor will typically verify: evidence of routine maintenance (logbook entries, overhaul reports), external condition (absence of leaks, secure mounting), satisfactory operation (no unusual noise/vibration), and compliance with manufacturer's service bulletins. If the turbocharger is opened for inspection (e.g., during a major overhaul), bearing clearances and rotor condition will be checked and documented. The surveyor may also request to witness a turbocharger overspeed trip test if the system allows for it, or verify its last test date.