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Project

Top Overhauling of NIIGATA 8L-28HX Main Engines on Harbour Tug in India

Table of Contents

Background

Industry
Marine
Solution
Top Overhaul (ToH)
of Main Engine
Make & Model
NIIGATA 8L-28HX
Main Engines
Asset
Harbour Tug

Summary About The Project

Neptunus successfully completed the top overhauling of twin NIIGATA 8L-28HX main engines onboard a harbour tug operating in India. The maintenance was carried out after both engines accumulated approximately 45,563 running hours to restore engine reliability, improve operational performance, and ensure safe continued operation.

The scope included complete dismantling, inspection, cleaning, calibration, servicing, testing, renewal, and reassembly of major engine systems in accordance with OEM recommendations. Critical systems including cylinder heads, fuel injection equipment, piston assemblies, cylinder liners, camshaft assemblies, air starting systems, cooling systems, crankshaft components, and safety systems were overhauled and inspected.

Following completion of the overhaul, successful load trials were conducted at 75% and 100% engine load. All engine operating parameters including engine speed, lubrication pressure, cooling water pressure, exhaust temperatures, peak cylinder pressures, and fuel injection settings were found within acceptable operating limits, confirming stable engine performance.

Planning

  • Team Composition: Neptunus team of 5, led by the Team Leader
  • Duration: 29 August 2025 to 13 September 2025
  • Work Scope:
    Complete top overhauling including dismantling, inspection, cleaning, calibration, component renewal, reassembly, testing, and load trials.

Procedure Carried Out

1. Cylinder Heads:
  • All cylinder heads removed from both port and starboard engines
  • Cylinder heads dismantled, cleaned, and inspected
  • Carbon deposits removed from combustion surfaces
  • Dye penetrant testing carried out on cylinder heads, inlet valves, and exhaust valves
  • Cracks detected on starboard engine exhaust valve seats of Units 1 and 8
  • Defective exhaust valve seats renewed with new components
  • Hydro pressure testing carried out at 6 kg/cm² for 15 to 20 minutes
  • Valve guide O-rings and cotters renewed
  • Valve springs, valve guides, valve rotators, and valve seats reused after inspection
  • Cylinder heads assembled with new gaskets
  • Cylinder heads installed and tightened as per OEM recommendations
  • Valve lash adjusted to OEM specifications
2. Rocker Arm and Valve Mechanism:
  • Rocker arm assemblies dismantled and cleaned
  • Rocker arm shaft and bushings measured
  • All measurements found within OEM limits
  • Rocker arm assemblies reused after inspection
  • Valve clearances adjusted to 0.50 mm for inlet and exhaust valves
3. Fuel Injection System:
  • All fuel injectors dismantled, cleaned, and inspected
  • Injector nozzles and O-rings renewed
  • Injector bodies lapped before assembly
  • Injector opening pressure calibrated to 33 MPa
  • Spray pattern, pressure holding, and leakage tests completed
  • Fuel injection pumps dismantled and overhauled
  • Delivery valves, barrels, plungers, O-rings, backup rings, and gaskets renewed
  • Fuel injection timing verified before and after overhaul
  • Fuel injection pumps installed and tightened according to OEM recommendations
4. Air Starting System:
  • Air starting valves dismantled, cleaned, and inspected
  • Valve seats lapped
  • Functionality of all valves verified
  • O-rings and gaskets renewed
  • Starting air distributors cleaned and inspected
  • Fresh grease applied before installation
5. Piston and Connecting Rod Assembly:
  • Piston and connecting rod assemblies removed
  • Pistons and connecting rods dismantled and cleaned
  • Piston crowns dye penetrant tested
  • Connecting rods and big end cap serrations dye penetrant tested
  • Piston pin diameters measured
  • Small end bushings inspected
  • Big end bore measurements recorded
  • All readings found within OEM limits
  • All piston rings renewed
  • Big end bearings reused except Port Engine Unit 1
  • New big end bearings installed on Port Engine Unit 1
  • Piston ring groove clearances checked
  • Piston ring end gaps measured
  • Assemblies installed and tightened according to OEM recommendations
6. Cylinder Liners:
  • All cylinder liners cleaned
  • Cylinder liners honed
  • Measurements recorded before and after honing
  • All liner dimensions found within OEM limits
  • New liner O-rings installed during assembly
7. Cylinder Block :
  • Cylinder blocks cleaned thoroughly
  • Cylinder head mounting surfaces cleaned
  • Cooling water jacket areas cleaned
  • Cooling water joint pipe seals renewed
  • Rubber joints renewed
  • O-rings renewed before assembly
8. Camshaft and Valve Train:
  • Camshafts cleaned and inspected
  • Cam galleries cleaned
  • Cam bearing clearances measured
  • Cam bearing clearances found within limits
  • Camcase covers cleaned
  • New camcase gaskets installed
  • Tappet rollers dismantled, cleaned, and inspected
  • Tappet roller assemblies reinstalled
9. Main Bearings and Crankshaft:
  • Main bearings of selected units removed for inspection
  • Upper and lower bearing shells visually inspected
  • Bearing condition found satisfactory
  • Crankshaft web deflection measured
  • All deflection readings found within OEM permissible limits
10. Cooling System:
  • Jacket cooling water pumps overhauled
  • Mechanical seals renewed
  • Bearings renewed
  • Oil seals renewed
  • O-rings renewed
  • Gasket kits renewed
  • Sea water pumps replaced with new units
  • Cooling water passages cleaned and inspected
11. Exhaust and Air Intake System:
  • Exhaust manifold expansion joints visually inspected
  • Exhaust manifold gasket surfaces cleaned
  • New exhaust manifold gaskets installed
  • Inlet manifolds cleaned and inspected
  • Inlet manifold gaskets renewed
  • Fuel injection unions cleaned
  • Fuel injection pipes internally inspected
  • Fuel system sealing O-rings renewed
12. Crankcase and Safety System:
  • Crankcases cleaned thoroughly
  • Oil sumps cleaned
  • Internal inspection carried out jointly with customer representatives
  • Overspeed trip air cylinders function tested
  • Engine safety system verified
13. Pre-Commissioning and Load Trials:
  • Pre-commissioning inspections completed
  • Load trials conducted at 75% and 100% engine load
  • Engine operation verified at 600 RPM and 750 RPM
  • Lube oil pressure monitored
  • Cooling water pressure monitored
  • Fuel oil pressure monitored
  • Turbocharger lubrication pressure monitored
  • Cooling water temperatures recorded
  • Peak cylinder pressures recorded
  • Exhaust gas temperatures monitored
  • Fuel injection rack settings verified
  • All engine operating parameters confirmed within acceptable OEM operating limits

Scope for Improvement

  • Maintain lube oil quality through regular filtration and oil condition monitoring
  • Repair and maintain special maintenance tools required for major engine overhauls
  • Continue maintaining adequate onboard emergency spare parts inventory

Recommendations

  • Closely monitor both engines during the first 100 running hours after overhaul
  • Investigate any abnormal vibration, unusual noise, leakage, or operating parameter fluctuation immediately
  • Replace and inspect lube oil filters after the first 100 operating hours
  • Conduct lube oil analysis after the first 100 running hours
  • Regularly monitor lube oil pressure, cooling water temperature, exhaust temperatures, and fuel system performance
  • Check fuel condition periodically for contamination or fuel dilution
  • Follow OEM starting, stopping, inspection, and preventive maintenance procedures
  • Use 100% cotton cleaning rags during future overhaul activities
  • Plan the next major overhaul according to OEM recommended maintenance intervals

Conclusion

Neptunus successfully completed the top overhauling of twin NIIGATA 8L-28HX main engines onboard a harbour tug in India through systematic dismantling, inspection, cleaning, calibration, component renewal, testing, and reassembly in accordance with OEM procedures.

The overhaul included renewal of defective exhaust valve seats, piston rings, fuel injection pump components, injector parts, cooling system seals, and various engine gaskets while confirming all critical calibration measurements remained within OEM limits.

Following successful load trials, engine speed, lubrication pressure, cooling system performance, fuel injection settings, cylinder peak pressures, and exhaust temperatures were verified within acceptable operating limits, confirming reliable engine operation.

This project demonstrates Neptunus expertise in delivering comprehensive top overhauling services for NIIGATA marine main engines, ensuring improved reliability, operational efficiency, and long-term performance for harbour and marine applications.

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