7L51/60G

Common issues

• Ignition system failures (spark plug fouling/wear, ignition coil breakdown, pre-chamber issues) leading to misfires or unstable combustion.
• Gas admission valve leakage or sticking, affecting fuel distribution and combustion efficiency, potentially causing high exhaust temperatures or knocking.
• Turbocharger fouling (compressor/turbine side) or bearing wear, leading to reduced boost pressure, surging, or high exhaust back pressure.
• Cylinder liner wear or scuffing, though generally lower than HFO engines, can occur due to poor lubrication, combustion issues, or abrasive particles.
• Exhaust valve seat wear, burning, or leakage, resulting in loss of compression and increased exhaust gas temperatures.
• Piston ring sticking or breakage, leading to increased lube oil consumption, blow-by, and reduced power output.
• Engine Control System (ECS) sensor malfunctions (e.g., knock sensors, pressure/temperature transducers) causing false alarms or derating.
• Combustion instability (e.g., misfires, pre-ignition, knocking) often linked to gas quality, air-fuel ratio control, or ignition system performance.

Inspection checklist

• Visual inspection for gas, lube oil, and cooling water leaks around the engine, fuel gas train, and associated piping.
• Check the integrity of the fuel gas supply system, including double-walled piping, ventilation, gas detectors, and emergency shutdown valves.
• Inspect the ignition system components (spark plug leads, ignition coils, pre-chambers if accessible) for signs of damage, arcing, or corrosion.
• Monitor exhaust gas temperatures (EGTs) for individual cylinders; significant deviations indicate combustion issues (e.g., misfire, poor injection).
• Check turbocharger condition: inspect compressor and turbine blades for fouling or damage, listen for abnormal bearing noise, and verify boost pressure.
• Verify crankcase pressure and oil mist detector (OMD) functionality; check for abnormal crankcase breathing.
• Inspect valve gear (rocker arms, pushrods) for proper lubrication and excessive clearances; listen for abnormal knocking or tapping sounds.
• Review engine control system (ECS) alarms, event logs, and performance data for any recurring faults or operational anomalies.
• Check cooling water system pressures, temperatures, and expansion tank levels; inspect heat exchangers for signs of leakage or fouling.
• Assess engine room ventilation and gas detection system status, ensuring proper operation and calibration.

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 spark plugs and ignition coils (at least for one cylinder, preferably more).
• Gas admission valve complete unit or repair kit (seals, springs).
• Fuel gas filter elements (various stages).
• Piston rings (complete set for at least one cylinder).
• Exhaust valve and inlet valve (at least one of each, with springs and rotators).
• Turbocharger bearing cartridge or complete rotor assembly.
• Critical engine control system (ECS) sensors (e.g., knock sensor, speed sensor, pressure/temperature transducers).
• High-pressure fuel gas pump seals/repair kit (if applicable to specific gas train design).

Safety

• Gas leakage and explosion risk: Methane is lighter than air; ensure proper ventilation, gas detection, and emergency shutdown systems are functional.
• High voltage from ignition system: Exercise extreme caution when working near spark plugs and ignition coils, especially when the engine is running or recently stopped.
• Fire hazard: Presence of flammable gas requires strict adherence to hot work permits and fire prevention measures.
• Asphyxiation risk: Potential for inert gas purging in gas lines or CO2 release from fire fighting systems; ensure proper ventilation and personal protective equipment.
• Crankcase explosion risk: Although less common than with HFO, proper functioning of oil mist detectors and crankcase relief valves is vital.

Class survey

Class surveyors will meticulously check the entire fuel gas system, including double-walled piping integrity, ventilation systems for gas-safe areas, gas detection system calibration and alarm functionality, and emergency shutdown sequences. They will review engine running hours, maintenance records, lube oil analysis reports, and gas consumption data. Emphasis will be placed on the condition of safety devices such as oil mist detectors, crankcase relief valves, and overspeed trip. Performance parameters like exhaust gas temperatures, pressures, and power output will be scrutinized. Any overhauling records for cylinder heads, pistons, and turbochargers will be verified, along with the onboard spare parts inventory for critical gas engine components. Visual inspection for leaks, abnormal wear, and general cleanliness of the engine and surrounding spaces is standard.

Estimated lifetime: 80,000 - 100,000 running hours before major refurbishment or replacement of major components (e.g., crankshaft, engine block), assuming diligent maintenance.