AT25

Common issues

• Compressor wheel fouling or damage (e.g., from foreign object ingestion, erosion)
• Turbine wheel fouling, erosion, or thermal cracking (especially at blade roots)
• Bearing distress (journal and thrust bearings) leading to increased clearances, noise, or failure
• Oil leakage from bearing housing seals, oil lines, or casing joints
• Rotor imbalance or excessive vibration due to fouling, damage, or bearing wear
• Exhaust gas leakage from turbine casing joints, expansion bellows, or manifold connections
• Air filter blockage leading to reduced compressor efficiency and surging
• Surging during engine load changes, often indicative of fouling or engine issues

Inspection checklist

• Visual check for oil leaks around bearing housing, oil lines, and casing joints.
• Visual check for exhaust gas leaks around turbine casing, expansion joint, and exhaust manifold.
• Inspect air filter element for cleanliness, damage, and proper seating.
• Manually check rotor for free rotation and excessive axial/radial play (engine stopped, cold). Typical axial play for AT25: 0.10-0.25mm new, max 0.35-0.45mm worn.
• Borescope inspection of compressor and turbine blades for fouling, erosion, cracks, or foreign object damage (if not opened for overhaul).
• Monitor turbocharger speed, boost pressure, and exhaust gas temperatures (inlet/outlet turbine) during engine operation.
• Listen for abnormal noises (e.g., whining, grinding, rubbing) and observe for excessive vibration during operation.
• Verify cooling water flow and temperature (if water-cooled bearing housing/pedestal) and check for leaks.
• Check condition of flexible mounts and securing bolts for tightness.

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 set of journal bearings (typically 2 pcs)
• Complete set of thrust bearings (typically 1 pc)
• Gasket and O-ring set for routine overhaul (e.g., bearing housing, casing joints)
• Sealing rings (compressor and turbine side)
• Air filter element
• Oil filter element (if internal oil system or external pump)
• High-speed balancing kit (if workshop overhaul is performed onboard and personnel are trained)

Safety

• Extreme temperatures: Exhaust gas and turbine casing can reach 400-600°C. Risk of severe burns. Always allow adequate cooling time before inspection/maintenance.
• High rotational speed: Rotor operates at 20,000-60,000+ RPM. Never attempt to work on a running turbocharger. Ensure engine is stopped and locked out.
• High pressure: Boost air pressure (2-4 bar) and exhaust gas pressure. Ensure systems are depressurized before opening any casings or lines.
• Oil mist/leakage: Potential fire hazard if lubricating oil leaks onto hot surfaces. Ensure proper sealing and clean up any spills immediately.
• Noise: High noise levels during operation require mandatory hearing protection.

Class survey

Class surveyors typically verify maintenance records (logbook entries, overhaul reports), conduct a visual inspection for leaks, damage, and proper securing. They will check operational performance parameters (boost pressure, exhaust temperatures, speed) against design values. If the turbocharger has been opened for maintenance, the surveyor may inspect the rotor, bearings, nozzle ring, and diffuser for condition and clearances. Confirmation of critical spare parts availability and condition of safety devices (e.g., overspeed trip, if fitted) is also common.