Home » Projects » On-Time Completion of Major Overhaul of Niigata 6MG-L-28-AHX Main Engines Onboard an Offshore Support Vessel in Abu Dhabi
Table of Contents
Project
On-Time Completion of Major Overhaul of Niigata 6MG-L-28-AHX Main Engines Onboard an Offshore Support Vessel in Abu Dhabi
Table of Contents
Background
Industry
Oil & Gas
Solution
Major Overhaul
(MOH)
Make & Model
Niigata 6MG(L)28AHX
Main Engines
Asset
Offshore Support
Vessel (OSV)
The project involved a major overhaul of both main propulsion engines onboard Crest Argus 5, an Offshore Support Vessel operated by OFCO. The vessel was equipped with two NIIGATA 6MG-[L]-28-AHX main engines (800 RPM / 2220 kW), with the STBD engine at 9312 hours and the PORT engine at 9249 hours. Given the criticality of offshore operations, the engines required a comprehensive 24k major overhauling to ensure operational safety, reliability, and extended service life.
Summary About The Project
Neptunus undertook the end-to-end overhaul of both engines covering cylinder heads, liners, pistons, bearings, valve systems, injectors, fuel pumps, camshaft, governor, and associated assemblies. After meticulous reassembly and testing, both engines were restored to full operational readiness. The project was completed within the stipulated timeline, followed by successful no-load and sea trials, ensuring the vessel was fit for continued service.
Planning
Team Composition: A team of 6 engineers guided by experienced Team Leader
Duration: 26 July – 10 September 2025 (approx. 45 days).
Work Scope: Comprehensive 24k overhaul of two Niigata 6MG(L)28AHX Engines, including dismantling, inspection, servicing, replacement of critical parts, reassembly, and trials.
Procedure Carried Out
1. Cylinder Heads: - Removed and sent to workshop for dismantling, decarbonizing, dye penetrant testing, and hydro testing. - Replaced valve seats, guides, rotators, springs, O-rings, and reassembled with new gaskets.
2. Valves & Fuel Injectors: - Renewed all intake/exhaust valves and valve seats. - Overhauled injectors with pressure testing (50 MPa). One faulty nozzle replaced.
3. Fuel Injection Pumps: - Dismantled, cleaned, and rebuilt using new delivery valve assemblies, plungers, and seals.
4. Pistons & Connecting Rods: - Cleaned and tested piston crowns. - Replaced piston rings, snap rings, and big-end bearings. - Conducted torque and angle tightening as per OEM guidelines.
5. Cylinder Liners & Block: - Removed liners for cleaning and honing. - Renewed O-rings and seals, calibrated bores, and reinstalled. - Cleaned engine block surfaces, cam galleries, and exhaust systems.
6. Bearings & Crankshaft: - Replaced all main bearings; thrust bearings reused (within limits). - Conducted crankpin diameter and crank web deflection checks (all within tolerance).
7. Valve Gear, Camshaft & Layshaft: - Inspected valve gear assemblies and replaced worn parts. - Checked camshaft clearances (satisfactory). - Renewed layshaft bearings, spring pins, and linkage ball bearings.
8. Governor & Drive: - Governor overhauled at Goltens Workshop, reinstalled after completion. - Checked gear backlash and replaced bearings.
9. Pumps & Auxiliary Systems: - Oil pumps dismantled, inspected, and reused (good condition). - Water pump service deferred as per customer’s instruction (to be addressed in next maintenance).
10. Pre-Commissioning & Trials: - Verified lubrication, cooling, and fuel systems integrity. - Conducted no-load trials at 400 and 800 RPM – parameters found normal. - Final sea and load trials completed successfully, confirming restored performance.
Result
Both Niigata 6MG(L)28AHX Engines were restored to reliable operating condition with all parameters stable during trials. The vessel was handed over to the customer on 10 September 2025. The overhaul improved operational readiness, extended engine life, and assured performance for the next maintenance cycle.
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