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Mitsubishi

6UEC85LSII

Name: Mitsubishi 6UEC85LSII
Brand: Mitsubishi
SKU: OSE-38595

The Mitsubishi 6UEC85LSII is a six‑cylinder, low‑speed two‑stroke marine diesel engine delivering up to 22 680 kW at 76 rpm, designed for large cargo vessels and compliant with IMO Tier II emissions.

22680.0 kW

Power

1,050,000 kg

Weight

Engine Specifications

Cylinders

850 mm

Bore

3150 mm

Stroke

22,680 kW

MCR Power

76.0 rpm

MCR RPM

18.5 bar

MEP

2-stroke

Stroke Type

Family: Mitsubishi UEC (LS/LA/LSE/LSII) · Tier: IMO Tier II · Fuel: HFO, MDO

Inspector Detail ✓ verified

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Designation decoded

6-cylinder Mitsubishi UEC 85 cm bore, Long Stroke II (LSII) series. Large crosshead two-stroke engine with conventional camshaft control, 850 mm bore and 3150 mm stroke. Heavy-duty design for main propulsion of large merchant vessels.

Background

The 6UEC85LSII is one of the largest engines in the UEC series with 850 mm bore and impressive 3150 mm stroke, resulting in a very high stroke-to-bore ratio of 3.706. With a mean effective pressure of 18.5 bar, this machine delivers considerable power for VLCCs and large bulk carriers. The 850 mm bore class requires dry dock for major component work due to the enormous weight of individual parts.

Calculated metrics

Stroke To Bore Ratio

3.706

Mean Effective Pressure Bar

18.5

Inspector checklist

Zylinderinspektion (Schwerlastkomponenten)

Record cylinder liner wear at prescribed measuring points – with 850 mm bore, pay particular attention to ovality
Kolbenringe vermessen (Stoßspiel, Axialspiel) – schwere Ringe erfordern spezielle Handhabung
Check piston crown for cracks (penetrant dye or MPI method)
Examine exhaust ports and scavenge air passages for coke deposits and erosion
Laufbuchsen-Kühlwasserraum auf Kavitationsschäden inspizieren

Propulsion machinery and heavy-duty bearing

Check crosshead bearing at 850 mm bore particularly carefully for scoring marks and bearing shell condition
Control connecting rod bolts with ultrasonic testing for elongation – critical for these component sizes
Inspect piston rod surface and stuffing box
Measure crankshaft deflection – tight tolerances with large bore
Inspect main bearing and document oil clearance

Brennstoffeinspritzung

Test fuel injection valves on test stand – note high injection pressures at 18.5 bar MEP
Brennstoffpumpen-Verschleißzustand beurteilen
Measure camshaft timing and cam profiles
Check high-pressure lines for fatigue – vibration stress high on large engine

Abgassystem

Abgastemperaturen zwischen Zylindern vergleichen (340–420 °C, max. 30 °C Spreizung)
Exhaust valves to be checked for burn-through and corrosion – particularly stressed at high MEP
Turbolader-Zustand inspizieren (große Einheiten, schwere Rotoren)
Exhaust manifold and expansion joints to be checked

Trockendock-spezifische Prüfungen

Foundation bolts and engine installation to be inspected
Propellerwellen-Ausrichtung zur Kurbelwelle verifizieren
Seawater cooling system and sea chests to be inspected
Hull deformation and influence on deflection to be assessed

Sicherheitseinrichtungen

Oil mist detector to be calibrated and tested
Überdruckventile an allen Zylindern prüfen
Überdrehzahlschutz verifizieren
Notabstellvorrichtung auf Funktion testen

Logbook reference values

Parameter	Expected	Deviation means
Exhaust gas temperature per cylinder	340–420 °C	Elevated temperatures on one cylinder indicate fuel injection or compression problems
Pmax-Zylindergleichmäßigkeit	±3 bar zwischen Zylindern	Überschreitung zeigt unterschiedliche Verbrennung an – sofortige Ursachenanalyse erforderlich
Mittlerer effektiver Druck (MEP)	18.5 bar (Nennlast)	Deviation indicates power loss due to wear or adjustment problems
Spülluftdruck	2.0–3.5 bar (lastabhängig)	Low pressure indicates turbocharger or charge air cooler problem
Zylinderöl-Feedrate	0.7–1.2 g/kWh	Deviation significantly affects wear and operating costs at this engine size
Kühlwasser-Temperatur Austritt	80–85 °C	Exceeding limit may indicate gas blow-by or deposits
Kurbelwellendurchbiegung	According to manufacturer table, tight tolerances at 850 mm bore	Deviation indicates foundation settlement or hull deformation – particularly to be verified in dry dock
Systemöl-Druck	2.5–5.0 bar	Pressure drop requires immediate inspection of oil pump and filter

Common Failure Modes

Cylinder liner cracks due to thermal stress

Symptoms: ['Kühlwasserverlust', 'Wassereinbruch in Spülluftkasten', 'Druckverlust im Zylinder']

Causes: Extreme thermal cyclic stress at 850 mm bore, Kavitation auf der Kühlwasserseite, Unzureichende Kühlwasserbehandlung, Material defect at this component size

Preventive: Cooling water chemistry to be strictly monitored, cylinder liner to be inspected for cracks at every piston removal (dye penetrant), cavitation protection anodes to be checked

Kreuzkopflager-Fressschaden

Symptoms: ['Stark erhöhte Lagertemperatur', 'Metallabrieb im Schmieröl', 'Klopfgeräusche']

Causes: Oil film rupture due to high specific bearing load at 18.5 bar MEP, Schmierölverunreinigung, Misalignment due to foundation deformation

Preventive: Lubricating oil pressure and temperature to be continuously monitored, oil analyses at shortened intervals, bearing clearance to be measured at every major overhaul

Kolbenkronen-Rissbildung

Symptoms: ['Gasübertritt', 'Erhöhte Abgastemperatur', 'Druckverlust']

Causes: Thermal fatigue at high combustion pressures, Hot corrosion due to vanadium, Unzureichende Kolbenkühlung

Preventive: Piston crowns to be inspected by NDT (dye penetrant, MPI) at every removal, piston cooling oil flow and temperature differential to be monitored

Foundation deformation and alignment problems

Symptoms: ['Veränderte Deflection-Werte', 'Erhöhte Lagertemperaturen', 'Ungewöhnliche Vibrationen']

Causes: Hull deformation due to cargo loading, Korrosion der Doppelboden-Struktur, Ungleichmäßige Ballastierung

Preventive: Deflection values to be measured at various loading conditions, dry dock alignment to be performed using optical or laser methods

Turbocharger bearing damage in large units

Symptoms: ['Vibrationen am Turbolader', 'Erhöhte Lagertemperatur', 'Rauchentwicklung am Turbolader']

Causes: High rotor mass in large turbochargers, Ölverunreinigung, Blade fracture due to foreign objects

Preventive: Turbolader-Lagerung gemäß Herstellerintervall inspizieren, Ölfilter vor Turbolader regelmäßig wechseln, Ansaugfilter kontrollieren

Expert tips

💡 At 850 mm bore, component handling is a safety issue – lift capacity and sling certification must be verified before each piston pull; these operations typically require dry dock or specialized port facilities.
💡 The high MEP of 18.5 bar places significant stress on engine components – ultrasonic measurement of connecting rod bolts at every overhaul is not an option but mandatory.
💡 At 6-cylinder configuration with 850 mm bore, pay particular attention to vibration characteristics – inspect torsional damper and thrust bearing at shortened intervals.

Related components

Turbocharger (large units, special maintenance) Ladeluftkühler (großflächig, Korrosionsanfällig) Nockenwellenantriebskette (hohe Lasten) Main bearing and thrust bearing Foundation bolts and engine installation Piston cooling oil system and telescopic pipes Fuel pumps and fuel injection valves Reversing clutch and control air distributor Vibration damper and flywheel Exhaust gas boiler and soot blowing device

Classification & regulatory

MARPOL Annex VI, NOx Tier II/III depending on year of build and trading area. At 850 mm bore, class surveys are often coupled with dry dock intervals. Pmax and MEP must be documented in the Engine Technical File – deviations from 18.5 bar MEP require class notification. Heavy components require special inspection of lifting equipment certificates. J-ENG (from 2018) as successor builder to be noted.

Reference content for inspector orientation. Always verify against manufacturer's manual, latest service letters and class society requirements.