Main Engine 4-Stroke · Main Engines (4-Stroke)
The MAN 7LL21/31 is a 7‑cylinder medium‑speed main engine delivering up to 1 540 kW at 1000 rpm, featuring common‑rail fuel injection and flexible fuel capability (MGO, HFO, bio‑fuels, methanol retrofit).
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| Fuel Injector Overhaul | 3,000 - 6,000 hours (depending on fuel quality) |
|---|---|
| Exhaust Valve Overhaul | 6,000 - 12,000 hours |
| Piston Overhaul (inspection/ring replacement) | 12,000 - 18,000 hours |
| Cylinder Head Overhaul (complete) | 12,000 - 18,000 hours |
| Turbocharger Major Overhaul | 12,000 - 24,000 hours |
| Main & Big End Bearing Inspection | 18,000 - 24,000 hours |
| Major Engine Overhaul | 36,000 - 48,000 hours |
| Cylinder Liner Wear (max taper/ovality) | 0.6 - 0.8 mm |
|---|---|
| Piston Ring Groove Axial Clearance (max) | 0.15 - 0.25 mm |
| Crankshaft Deflection (max permissible across adjacent throws) | 0.05 - 0.08 mm |
| Main Bearing Clearance (max) | 0.20 - 0.30 mm |
| Big End Bearing Clearance (max) | 0.15 - 0.25 mm |
| Exhaust Valve Seat Recession (max) | 0.8 - 1.2 mm |
| Turbocharger Rotor Axial Play (max) | 0.15 - 0.25 mm (refer to specific TC manufacturer data) |
Ranges are typical for this design class. Always confirm against the manufacturer documentation for your serial number.
Class surveyors typically focus on: 1. Documentation Review: Engine logbooks, maintenance records, lube oil analysis reports, fuel oil bunkering records, and previous survey reports. 2. Safety Devices Functionality: Verification of overspeed trip, low lube oil pressure shutdown, high cooling water temperature shutdown, and crankcase oil mist detector alarm/shutdown. 3. Crankshaft Deflection Measurement: Often required at specific intervals (e.g., every 2-3 years or 10,000-15,000 hours) to assess bearing and frame condition. 4. Bearing Inspections: Opening of main and/or big end bearings as per planned maintenance system or class requirements (e.g., every 18,000-24,000 hours). 5. Cylinder Head/Piston Overhaul Status: Verification of last overhaul dates and condition reports. 6. Fuel System Integrity: Close inspection of high-pressure fuel pipes, leak-off arrangements, and shielding for fire prevention. 7. Exhaust System & Turbocharger: General condition, insulation, and integrity of expansion bellows. 8. General Condition: Visual inspection for leaks, corrosion, loose fastenings, abnormal vibrations or noises, and overall cleanliness of the engine and surrounding area.
Estimated lifetime: 36,000 - 48,000 hours before major overhaul; total engine life significantly longer with proper maintenance and overhauls.
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