⚓ Working on this equipment?

Ask the AI troubleshooter, log your hours on board and turn them into invoice-ready service reports — for this exact model.

Start free — 14 days →

No credit card required

🔧 32 verified suppliers & service companies for Mitsubishi in the Maritime Network Find suppliers →

Is Mitsubishi your company? Claim this page

Mitsubishi

8UEC85LSII

Name: Mitsubishi 8UEC85LSII
Brand: Mitsubishi
SKU: OSE-38616

The Mitsubishi 8UEC85LSII is an eight‑cylinder low‑speed two‑stroke marine diesel engine delivering up to 46 400 kW at 76 rpm, designed for main propulsion on large commercial vessels.

46400.0 kW

Power

Engine Specifications

Cylinders

850 mm

Bore

2800 mm

Stroke

46,400 kW

MCR Power

76.0 rpm

MCR RPM

2-stroke

Stroke Type

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

Inspector Detail ✓ verified

▸

Designation decoded

8UEC85LSII – Mitsubishi 8-Zylinder, Unified Exhaust-valve Crosshead, 850 mm Bohrung, Langhub, Super-Mark-II-Ausführung (LSII). Größter Zweitakt-Kreuzkopfmotor der UEC85-Baureihe, Dry-Dock-Klasse.

Background

The UEC85LSII is the largest engine in the UEC series with 850 mm bore and 2800 mm stroke. With a stroke-to-bore ratio of 3.29, this is an ultra-long-stroke engine for the largest merchant ships such as VLCCs and Capesize bulk carriers. The 850 mm bore classifies this engine as a dry-dock machine – piston withdrawal and major overhauls require dry-dock stay due to component weights.

Calculated metrics

Stroke To Bore Ratio

3.29

Inspector checklist

Cylinder liner and piston (dry-dock work)

Measure liner wear in four planes and two axes – document for trend analysis
Renew piston rings completely or measure wear in detail
Kolbenkrone mittels NDT (UT/MT) auf Ermüdungsrisse prüfen
Kolbenkühlräume endoskopisch auf Ablagerungen inspizieren
Bei Kolbenziehung Gewicht beachten – Krankapazität im Trockendock sicherstellen

Auslassventil

Inspect valve seat and spindle for vanadium corrosion and erosion
Stellite-Panzerung auf Restdicke messen
Ventildrehvorrichtung auf korrekte Funktion testen
Hydraulischen Antrieb komplett überholen

Crosshead and running gear

Crosshead bearing clearance to be measured and documented
Kreuzkopfbolzen mittels UT auf Ermüdungsrisse prüfen
Check connecting rod stud bolts for preload and condition
Document crosshead shoe wear and surface quality

Crankshaft and main bearing

Kurbelwellen-Deflexion an allen Kröpfungen messen
Hauptlager-Spiel kontrollieren
Inspect bearing shells for fatigue and cavitation
Check foundation and engine frame for crack formation

Fuel and injection system

Einspritzpumpen komplett überholen
Renew high-pressure lines or inspect for cracks
Test fuel valves for seating and spray pattern

Turbocharger and charge air system

Turbocharger general overhaul at class survey
Inspect charge air cooler tube bundle for corrosion and leakage
Thoroughly clean and inspect scavenge air box

Logbook reference values

Parameter	Expected	Deviation means
Exhaust gas temperature per cylinder	340–420 °C	Zylinderweise Abweichung >30 °C deutet auf schwere Verbrennungsstörung hin
Pmax (Zünddruck)	±3 bar vom Sollwert	Signifikante Abweichung erfordert sofortige Einspritzsystem-Überprüfung
Spülluftdruck	2,5–4,0 bar	Low pressure at full load indicates turbocharger degradation
Kolbenkühlöl-Rücklauftemperatur	Max. 45 °C über Vorlauf	Increased difference is critical at 850 mm piston – immediate investigation required
Kurbelwellen-Deflexion	Gemäß Mitsubishi-Tabelle für 850mm-Klasse	Exceeding limit values is particularly serious at this engine size – check foundation deformation
Zylinderöl-Feedrate	0,6–1,0 g/kWh	Increased consumption at 850 mm bore means significant cost impact
Schmieröltemperatur vor Motor	40–47 °C	Elevated temperature can indicate bearing wear in the heavily loaded bearings
Scavenge air temperature after cooler	35–50 °C	Überhöhte Temperatur verschlechtert Ladungswechsel signifikant

Common Failure Modes

Kolbenkronen-Thermische-Ermüdung

Symptoms: ['Erhöhte Kolbenkühlöl-Temperatur', 'Blow-by im Spülluftkasten', 'Visible cracks at NDT inspection']

Causes: Extreme thermal stress at 850 mm piston diameter, Häufige Laständerungen, Insufficient piston cooling due to deposits

Preventive: Check piston crown at each drydock overhaul by means of UT; clean cooling spaces; limit load change gradient

Hauptlager-Ermüdung

Symptoms: ['Erhöhte Lagertemperatur', 'Metallpartikel im Schmieröl', 'Deflexionswerte außerhalb Toleranz']

Causes: High bearing load in 850 mm class, Foundation deformation due to hull girder bending, Ölverunreinigung

Preventive: Inspect main bearing at each drydock visit; check foundation for cracks; deflection measurements every 6 months

Stuffing box wear (intensified)

Symptoms: ['Ölverlust an der Stopfbuchse', 'Verschmutzung des Spülluftbereichs', 'Erhöhter Schmierölverbrauch']

Causes: Große Kolbenstangen-Oberfläche beschleunigt Dichtungsverschleiß, Kolbenstangen-Oberflächenschaden, Thermische Verformung

Preventive: Replace stuffing box rings at shortened intervals; inspect piston rod surface at every opportunity

Kurbelgehäuse-Explosion (Risikoerhöhung)

Symptoms: ['Ölnebeldetektor-Alarm', 'Hot-Spot an Lagerstellen', 'Erhöhte Kurbelgehäuse-Temperatur']

Causes: Hot running at bearings or guide surfaces, Unzureichende Ölnebeldetektierung, Schmierölmangel

Preventive: Calibrate oil mist detectors monthly; check crankcase safety valves semi-annually; implement bearing wear monitoring

Expert tips

💡 The 850 mm bore makes this engine a drydock machine – piston weights exceeding 3 tonnes require crane capacity not available on board. Plan all major overhauls in drydock and provide spare parts in good time.
💡 For this engine size, pay special attention to foundation stiffness – deformations of the hull girder are transmitted directly to main bearing load and crankshaft deflection. Document tank loading conditions during deflection measurements.
💡 The 8-cylinder arrangement offers the best mass balancing, but the enormous engine length requires special attention to thermal expansion and engine mounting – check fixed bearing and sliding bearing positions at each survey.

Related components

Torsionsschwingungsdämpfer (große Ausführung) Axialdrucklager Elastic engine mounting and foundation bolts Kurbelgehäuse-Sicherheitsventile Oil mist detectors (all sections) Kolbenkühlöl-Teleskoprohre Kolbenabzugsvorrichtung (Trockendock-Ausrüstung) Nockenwellen-Antriebssystem Starting air distributor and valves Spülluftkasten-Rückschlagklappen

Classification & regulatory

IMO Tier II NOx limits. MARPOL Annex VI SOx compliance. IACS UR Z10.5 crankshaft deflection with special attention for 850 mm class. Drydock intervals according to classification society – coordinate engine overhaul with regular docking. Observe SOLAS requirements for engine room fire protection for engines of this size. Document special lifting requirements for components >2 t.

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