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Project

Complete Overhaul of YANMAR 6EY26 Main Engines on Multi-Purpose Offshore Vessel in Qatar

Table of Contents

Background

Industry
Marine
Solution
Major Overhaul of
Main Engines
Make & Model
YANMAR 6EY26
Main Engine
Asset
Multi-purpose
Offshore Vessel

Summary About The Project

Neptunus carried out a complete overhaul of both PORT and STBD YANMAR 6EY26 main engines onboard a multipurpose offshore vessel operating in Qatar after extended running hours. The objective was to restore engine performance, ensure safe operation, and improve long-term reliability.

The job included full dismantling, inspection, cleaning, machining checks, component replacement, and reassembly as per OEM standards. Critical systems such as cylinder heads, piston assemblies, fuel injection systems, cooling systems, crankshaft bearings, and lubrication systems were serviced and calibrated.

After completion, both engines were successfully tested under no-load and full-load conditions during sea trials. All parameters including pressure, temperature, and exhaust values were found within acceptable limits, confirming successful overhaul and stable engine performance.

Planning

  • Team Composition: Team of 7 technicians led by Team Leader
  • Duration: 24 February 2025 to 16 April 2025
  • Work Scope:
    Complete overhaul of PORT and STBD main engines including dismantling, inspection, component renewal, calibration, reassembly, and sea trials

Procedure Carried Out

1. Cylinder Head System:
  • Cylinder heads dismantled, cleaned, and inspected
  • Dye penetrant testing performed on combustion surfaces and valves
  • Valve seats replaced and machined for proper sealing
  • Injector sleeves renewed with O-rings and torque tightening as per OEM
  • Valve guides reused, valve rotators and steam seals renewed
  • Selected intake and exhaust valves replaced and remaining valves ground
  • Hydro pressure test conducted at 5 kg/cm² with no leakage
  • Cylinder heads reassembled and mounted with new gaskets
2. Piston and Connecting Rod Assembly:
  • Pistons, connecting rods, and bearings removed and cleaned
  • Crack testing performed on piston crowns
  • Piston rings replaced with clearance checks
  • Big end bearings and bolts renewed
  • Small end bush measurements recorded and verified within limits
  • Assemblies reinstalled as per OEM procedure
3. Cylinder Liner and Block:
  • Cylinder liners dismantled, cleaned, and calibrated
  • Honing carried out and post-honing measurements recorded
  • New O-rings installed and liners refitted
  • Engine block and oil sump cleaned thoroughly
  • Liner condition verified within permissible limits
4. Crankshaft and Bearing System:
  • Main bearing inspection carried out on selected units
  • One set of main bearings replaced on port side
  • Crankshaft deflection measured before and after overhaul
  • Crank pin diameter inspected and found within limits
5. Camshaft and Valve Mechanism:
  • Camshaft cleaned and inspected for wear
  • Cam bearing clearance checked and found satisfactory
  • Rocker arms dismantled, cleaned, and calibrated
  • Swing arm assemblies inspected and reused
6. Fuel Injection System:
  • Fuel injectors dismantled, cleaned, and calibrated at 34 MPa
  • New nozzles, seals, and O-rings installed
  • Fuel injection pumps overhauled with selective replacement of plunger barrels and delivery valves
  • Pump timing checked and verified
  • Fuel injection unions cleaned and resealed
7. Cooling and Lubrication System:
  • HT freshwater pumps overhauled with new spares
  • Lubricating oil pumps dismantled and bearings replaced
  • Oil coolers and air coolers chemically cleaned and pressure tested
  • Choked tubes cleared and flow restored
  • Filters cleaned and reinstalled
8. Turbocharger System:
  • Turbochargers dismantled and overhauled by third-party service provider
8. Pre-Commissioning and Sea Trial :
  • Lube oil priming and circulation checks completed
  • Safety systems tested including overspeed trip and emergency stop
  • No-load and full-load trials conducted successfully
  • Engine parameters monitored and found stable under all loads

Scope for Improvement

  • Ensure onboard availability of special tools for liner and piston handling
  • Improve maintenance and storage of emergency spare parts onboard
  • Strengthen preventive maintenance planning as per OEM guidelines

Recommendations

  • Monitor engine closely during first 100 hours post-overhaul
  • Inspect lube oil filters after initial running period
  • Conduct lube oil analysis after 150 hours of operation
  • Maintain strict monitoring of temperature and pressure parameters
  • Replace critical consumables as per OEM schedule

Conclusion

Neptunus successfully completed the overhaul of both PORT and STBD YANMAR 6EY26 main engines on a multi purpose offshore vessel operating in Qatar with full restoration of performance and reliability. Through systematic execution, precise calibration, and adherence to OEM standards, both engines were returned to service with stable operational parameters.

This project highlights Neptunus capability in delivering high-quality marine engine overhaul services for offshore operations.

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