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Table of Contents

Project

Major Overhaul of Niigata 6L28AHX Main Engines on Offshore Support Vessel

Table of Contents

Background

Industry
Oil & Gas
Solution
Major Overhaul (MOH) of Main Engines
Make & Model
Niigata
6L28AHX
Asset
Offshore Support
Vessel (OSV)
The vessel was due for a scheduled major overhaul of both Niigata main engines. The overhaul was required to restore performance, ensure reliability, and minimize the risk of unplanned breakdowns during critical operations.

Summary About The Project

The Neptunus team successfully completed a comprehensive Niigata Engine Overhaul and Repair onboard an offshore support vessel. The scope involved extensive inspection, reconditioning, and replacement of key engine components, including cylinder heads, valve assemblies, piston-connecting rod units, fuel systems, and cooling systems. The engines were reassembled and tested as per OEM standards. Post-sea trial performance confirmed the engines were operating in optimal condition.

Planning

Planned Duration: 30 Days

Work Overview:

  • Dismantling, inspection, and cleaning of major engine components
  • Replacement and calibration of worn-out parts
  • Reassembly as per OEM guidelines
  • Engine testing and trial operations

Procedure Carried Out

  • 1. Cylinder Heads: Cylinder heads were dismounted, dismantled, cleaned, and inspected. Dye penetrant and hydro pressure tests showed satisfactory results. New exhaust valve seats were installed on the starboard engine, while the port side seats were re-machined at the MAN workshop. All valve rotators and springs were replaced, followed by final cleaning, tappet settings, and mounting.
  • 2. Inlet & Exhaust Valves: Valves were selectively replaced and lapped. Port side valves were ground at the MAN workshop.
  • 3. Valve Guides & O-rings: All valve guides were inspected and calibrated in good condition; O-rings were renewed.
  • 4. Rocker Arms: Rocker arms were cleaned, calibrated, fitted with new O-rings, and reassembled.
  • 5. Pistons & Connecting Rods: Pistons and connecting rods were dismantled, cleaned, tested, and reassembled with new piston rings, big-end bearings, bolts, and studs.
  • 6. Cylinder Liners & Block: Liners were cleaned, honed by a third party, and reinstalled with new O-rings and fire rings. The cylinder block and oil sump were also cleaned.
  • 7. Crankshaft & Main Bearings: Crankshaft and main bearings were visually inspected and found in good condition. Minor scratches on STBD pins 1 and 6 were polished. Crankshaft deflection results were satisfactory.
  • 8. Cam Case & Valve Gear: The camshaft and valve gear were cleaned and inspected. New cam case gaskets were installed.
  • 9. Fuel Injection System: Injectors were cleaned, tested, and calibrated. FIPs (units 1, 3, 5) on both engines were overhauled with new components. Timing and fuel injection unions were checked, and O-rings were replaced.
  • 10. Governors & Drives: Both governors and housings were cleaned and reinstalled with new bearings. A new governor was fitted on the port engine, and the Halul 90 unit was used on the starboard engine.
  • 11. Turbochargers: Overhauled by a third party and installed by NPPS.
  • 12. Air Bypass & Wastegate: Linkage and bearings were checked; new bellows, clamps, and gaskets were installed.
  • 13. Geislinger Coupling: The port engine coupling was overhauled with new O-rings and reassembled as per OEM.
  • 14. Pumps & Coolers:
    - Fuel Oil Feed Pump (Port): Replaced with a new unit.
    - Sea Water Pump (STBD): Overhauled with new bearings and seals.
    - Freshwater Pumps: Overhauled on both engines with new spares.
    - Aftercoolers, Water Coolers, Oil Coolers: Cleaned and pressure-tested by the customer and reinstalled.
    - Oil Filters: Cleaned and reassembled by the customer.

Gallery

Block Before Cleaning
Block Before Cleaning
Block After Cleaning
Block After Cleaning
Centrifugal Filter Before Cleaning
Centrifugal Filter Before Cleaning
Centrifugal Filter After Cleaning
Centrifugal Filter After Cleaning
Cylinder Liner Before Honing Calibration
Cylinder Liner Before Honing Calibration
Cylinder Liner After Honing Calibration
Cylinder Liner After Honing Calibration
Cr Big End Calibration
Cr Big End Calibration
Cr Small End Calibration
Cr Small End Calibration
Cylinder Head Before Cleaning
Cylinder Head Before Cleaning
Cylinder Head After Cleaning
Cylinder Head After Cleaning
Cylinder Liner Ring Before
Cylinder Liner Ring Before
Cylinder Liner Ring After
Cylinder Liner Ring After
Geislinger Coupling Before Cleaning
Geislinger Coupling Before Cleaning
Geislinger Coupling After Cleaning
Geislinger Coupling After Cleaning
Piston Before Cleaning
Piston Before Cleaning
Piston Final Cleaned And Installation
Piston Final Cleaned And Installation
Peak Pressure Measurement
Peak Pressure Measurement

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