Mitsubishi S6U GenSet

Common issues

• Exhaust valve seat recession and burning, especially with HFO operation and poor fuel quality/treatment.
• Fuel injector nozzle fouling and carbon trumpet formation leading to poor atomization and combustion.
• Turbocharger compressor and turbine side fouling, reducing efficiency and increasing exhaust temperatures.
• Lube oil degradation and contamination (e.g., fuel dilution, water ingress, TBN depletion) due to HFO combustion byproducts.
• Cooling water system scaling or corrosion, leading to reduced heat transfer and localized overheating.
• High-pressure fuel pump element wear, causing reduced injection pressure and timing issues.
• Bearing wear (main and connecting rod) indicated by increased lube oil consumption or metal particle analysis.
• Cylinder liner wear and scuffing, often linked to poor lubrication or combustion.

Inspection checklist

• **Exhaust System:** Check for exhaust gas leaks from manifold joints, turbocharger casing, and expansion bellows. Monitor exhaust gas temperatures (individual cylinder and turbine inlet/outlet) for deviations. Listen for abnormal turbocharger noise/vibration.
• **Fuel System:** Inspect for fuel leaks (especially high-pressure lines), check fuel filter differential pressure, and verify fuel pressure/temperature at engine inlet. Visually inspect fuel pump racks for free movement.
• **Lube Oil System:** Check lube oil pressure (main and turbocharger), temperature, and level. Inspect for external leaks. Note any unusual color or smell of the oil. Review recent lube oil analysis reports.
• **Cooling System:** Inspect for cooling water leaks (fresh and seawater sides). Check cooling water temperatures and pressures. Verify proper operation of thermostatic valves. Inspect expansion tank level and condition.
• **Crankcase:** Listen for abnormal knocking or rumbling sounds. Check crankcase pressure/vacuum. Inspect crankcase relief valves for signs of leakage or damage. Perform a visual check for oil mist detector alarms.
• **General Engine Condition:** Look for signs of excessive vibration, loose fastenings, corrosion, or cleanliness issues. Check condition of engine mounts. Verify proper operation of local gauges and monitoring panel.
• **Safety Devices:** Confirm functionality of overspeed trip, low lube oil pressure shutdown, high cooling water temperature shutdown, and emergency stop buttons (if accessible for functional test).
• **Performance Data:** Review engine logbook for recent running parameters (load, speed, fuel consumption, exhaust temperatures, pressures) and compare against baseline or previous readings for trends.

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 Fuel Injector Assemblies (or Nozzles + Spindle Guides)
• Exhaust Valve Spindles and Seats (or complete valve cages)
• Turbocharger Bearing Cartridge and Seal Rings
• Full set of Engine Filters (Fuel, Lube Oil, Air)
• High-Pressure Fuel Pump Elements and Delivery Valves
• Starting Air Valve (complete unit or repair kit)
• Gasket and O-ring Kits for Cylinder Head and Fuel System
• Selected Sensors (e.g., exhaust temperature, pressure transducers)

Safety

• **High Temperatures:** Exhaust manifold, turbocharger, and engine surfaces operate at high temperatures, posing burn hazards. Ensure insulation is intact.
• **High Pressures:** Fuel injection system (up to 1500+ bar), starting air system (30 bar), and cooling water systems are under high pressure. Leaks can cause serious injury or fire.
• **Rotating Machinery:** Exposed rotating components like the flywheel, coupling, and turbocharger rotor present entanglement hazards. Ensure guards are in place.
• **Fire Hazard:** Leaks of hot fuel or lube oil onto hot surfaces can ignite, leading to engine room fires. Regular inspection for leaks and proper shielding is critical.
• **Noise Levels:** Engine room noise levels can exceed safe limits, requiring hearing protection during operation.

Class survey

A class surveyor will typically focus on the engine's overall condition, safety systems, and compliance with statutory regulations. Key checks include: verification of engine overspeed trip and other safety shutdowns (low lube oil pressure, high cooling water temp); integrity of fuel oil system (leakage, shielding of high-pressure lines, fire-resistant hoses); condition of exhaust gas piping and insulation; functionality of crankcase relief valves; security of engine foundation bolts; visual inspection for oil/water leaks, corrosion, and general cleanliness; review of engine logbooks, maintenance records, lube oil analysis reports, and performance data. They may request a load test to confirm satisfactory operation under load, especially during renewal surveys. Special attention will be paid to any modifications or repairs to ensure they meet class requirements.