SERVICE INTERVALS
When each part
is due.
Marine main engines are maintained on running-hours, not calendar dates. Wear parts are checked through the scavenge ports at short intervals, pulled for a top overhaul in the 12,000–18,000 hour band, and the running gear and bearings are renewed at a major overhaul closer to 60,000–100,000 hours. The ranges below are representative windows for large slow-speed two-stroke and medium-speed four-stroke engines — use them to plan spares lead time, not as a substitute for your engine's own maintenance manual.
| Component | Inspection | Top overhaul | Major overhaul | Typical wear limit |
|---|---|---|---|---|
| Cylinder liner | Scavenge-port wear check every 4,000–8,000 h | Hone / de-glaze when piston is drawn (~12,000–16,000 h) | Renew at ~60,000–100,000 h | Bore wear ~0.6–0.8% of diameter (max) |
| Piston & crown | Ring-zone and crown check at scavenge inspection (4,000–8,000 h) | Draw, clean, re-ring at ~12,000–18,000 h | Crown re-weld / renewal at ~30,000–48,000 h | Crown burn-down or groove wear beyond OEM limit |
| Piston rings | Butt-gap and face check at 4,000–8,000 h | Renew ring set at piston overhaul (~12,000–18,000 h) | Consumable — renewed each top overhaul | Radial thickness / butt clearance at maker limit |
| Cylinder cover & exhaust valve | Port inspection every ~6,000–8,000 h | Valve grind / seat re-face at ~12,000–16,000 h | Spindle & seat ring renewal at ~32,000–48,000 h | Seat burn or spindle recession beyond limit |
| Fuel valve / injector | Function / pop-test every ~2,000–4,000 h | Nozzle renewal & overhaul at ~4,000–8,000 h | Consumable — nozzles renewed each cycle | Opening-pressure drop or distorted spray pattern |
| Main & crankpin bearings | Clearance / crankshaft deflection check every 12,000–24,000 h | Open-up inspection (typically one unit per year) | Renew shells at ~60,000–90,000 h | White-metal wear-down or clearance above limit |
| Turbocharger | Routine water-wash; boroscope / bearing check at 8,000–16,000 h | Bearing renewal at ~16,000–24,000 h | Full rotor overhaul at ~24,000–40,000 h | Bearing clearance or rotor vibration at limit |
| Cylinder lubrication | Feed-rate and liner iron-content check (continuous / each inspection) | Lubricator / quill overhaul at ~16,000–24,000 h | System renewal with liner change | Feed rate held to guide value (~0.6–1.2 g/kWh) |
