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Sulzer

7RTA48T

Name: Sulzer 7RTA48T
Brand: Sulzer
SKU: OSE-38655

The Sulzer 7RTA48T is a medium-speed, two-stroke diesel main engine delivering 9 240 kW at 124 rpm, known for its conventional camshaft design and constant‑pressure turbocharging.

9240.0 kW

Power

Engine Specifications

Cylinders

480 mm

Bore

1900 mm

Stroke

9,240 kW

MCR Power

124.0 rpm

MCR RPM

2-stroke

Stroke Type

Family: Sulzer RTA · Tier: IMO Tier I · Fuel: HFO, MDO

Inspector Detail ✓ verified

▸

Designation decoded

7RTA48T – Sulzer 7-cylinder RTA series, 480 mm bore, tanker variant (T). Two-stroke crosshead engine with gear-driven camshaft, VIT, pulse lubrication and CLU.

Background

The 7RTA48T is a medium-sized two-stroke crosshead engine of the Sulzer RTA series with 480 mm bore and 1900 mm stroke, optimized for tanker service (T-variant). The 7-cylinder configuration is remarkable as it carries increased torsional vibration risk – odd cylinder numbers produce excitation orders that can lead to critical torsional vibrations in the shaft line. This requires special attention in vibration monitoring and torsional vibration damper. With a stroke-to-bore ratio of 3.96, this is a pronounced long-stroke engine for low speeds and direct propeller drive. The dimensions (480 mm bore) are moderate compared to the 840/960 mm variants, allowing maintenance work onboard without dry dock.

Calculated metrics

Stroke To Bore Ratio

3.958

Mean Effective Pressure Bar

18.5

Inspector checklist

Camshaft and gear drive

Inspect gear flanks for wear and pitting
Check camshaft bearing for clearance and condition
Examine cam profile for wear
Schmierölversorgung des Zahnradantriebs verifizieren

Torsional vibration and torsional vibration damper (7-cylinder!)

Inspect torsional vibration damper for function and condition – CRITICAL for 7-cylinder configuration
Check silicone oil fill level and viscosity of viscous damper
Perform torsional vibration measurement and compare with class requirements
Sperrbereiche der Drehzahl auf korrekte Einstellung im Steuerungssystem überprüfen
Inspect shaft line for torsion marks or fatigue indications

Cylinder liners and pistons

Laufbuchsenverschleiß mittels Innenmikrometer messen
Check piston rings for wear and gap
Check piston crown for thermal cracks and erosion
Laufflächenprofil über den gesamten Langhub beurteilen

VIT and injection system

VIT-Aktuator auf korrektes Ansprechen über den Lastbereich prüfen
Test injection nozzles for spray pattern and opening pressure
Kraftstoffhochdruckleitungen auf Ermüdungsrisse untersuchen
Ensure uniform injection across all 7 cylinders

Pulse lubrication and CLU

Calibrate CLU dosage uniformly for all 7 cylinders
Record and compare lubricating oil consumption per cylinder
BN-Management an die Betriebsbedingungen anpassen
Schmierquills auf Verstopfung prüfen

Crosshead and running gear

Kreuzkopflagerspiel messen
Check connecting rod bolts for preload
Inspect crosshead guides for wear
Examine piston rod for straightness and surface condition

Logbook reference values

Parameter	Expected	Deviation means
Maximaler Zünddruck (Pmax)	135–150 bar	Deviations between the 7 cylinders >5 bar indicate VIT misadjustment or fuel injection system irregularity
Exhaust gas temperature per cylinder	330–400 °C at rated load	Bei 7 Zylindern ist die gleichmäßige Temperaturverteilung besonders wichtig für den Schwingungsausgleich
Zylinderschmierölverbrauch	0,8–1,2 g/kWh	Deviations between the 7 cylinders indicate CLU imbalance or different wear condition
Torsionsschwingungsamplitude	Gemäß Torsionsschwingungsberechnung – Klassevorgaben einhalten	CRITICAL for 7-cylinder configuration: exceeding limit values can lead to shaft damage and coupling failure
Drehschwingungsdämpfer-Temperatur	max. 80 °C silicone oil temperature (depending on manufacturer)	Elevated temperature indicates degradation of damping medium or increased vibration excitation
Kompressionsdruck	105–125 bar	For long-stroke engine (S/B 3.96) compression pressure is performance-relevant – drop requires piston ring or valve inspection
Ladeluftdruck	2.2–3.0 bar abs. at rated load	Insufficient boost pressure impairs combustion and increases thermal stress
Kurbelwellendeflexion	max. ±0,05 mm/m	Bei 7-Zylinder-Anordnung ist die Deflexionsmessung an allen Lagerstellen besonders wichtig für die Erkennung von Torsionsschäden

Common Failure Modes

Torsionsschwingungsschaden an Wellenleitung

Symptoms: ['Erhöhte Schwingungswerte im Torsionsschwingungsmesssystem', 'Cracking at shaft flange or coupling bolt', 'Unusual noise or vibration from running gear', 'Drehschwingungsdämpfer-Überhitzung']

Causes: 7-Zylinder-Konfiguration erzeugt ungünstige Torsionsanregung, Defective or degraded torsional vibration damper, Betrieb in gesperrtem Drehzahlbereich, Change in system stiffness due to bearing wear

Preventive: Conduct torsional vibration measurement regularly and compare with design calculation, maintain and replace torsional vibration damper according to manufacturer specification, strictly adhere to barred speed ranges and program them correctly in control system

Piston rod fatigue in long-stroke engine

Symptoms: ['Oberflächenrisse an der Kolbenstange', 'Zunehmende Stopfbuchsenleckage', 'Veränderung der Kolbenstangenoberfläche']

Causes: Cyclic bending stress at S/B ratio of 3.96, Korrosionsinitiierte Rissbildung, Überschreitung der Ermüdungslebensdauer

Preventive: Non-destructive testing (MPI) of piston rod at every piston removal, ensure surface protection and polishing of running surface, observe operating hour limit

Ungleichmäßige Zylinderleistung (7-Zylinder)

Symptoms: ['Streuung der Abgastemperaturen >30 K', 'Unterschiedliche Zylinderdrücke', 'Vibration increase at certain load points']

Causes: Ungleichmäßige VIT-Einstellung über 7 Zylinder, Unterschiedlicher Einspritzdüsenzustand, CLU-Dosierungsungleichgewicht, Different running gear bore or piston ring condition

Preventive: Regelmäßige Leistungsgleichstellung aller 7 Zylinder, VIT-Kalibrierung über den gesamten Lastbereich, Einspritzdüsen als Satz austauschen, CLU-Gleichverteilung sicherstellen

Camshaft bearing wear

Symptoms: ['Veränderte Steuerzeiten', 'Geräuschentwicklung im Nockenwellenbereich', 'Erhöhte Öltemperatur am Nockenwellenlager', 'Metallpartikel im Schmieröl']

Causes: Mangelhafte Schmierung, Fluchtungsfehler, Ermüdung des Lagermaterials, Verunreinigung des Schmieröls

Preventive: Check lubricating oil quality and filtration regularly, measure bearing clearance during class survey, perform oil analysis for metal particles

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Related components

T o r s i o n a l v i b r a t i o n d a m p e r ( H I G H E S T P R I O R I T Y f o r 7 c y l i n d e r s ) , t u r b o c h a r g e r a n d c h a r g e a i r c o o l e r , p r o p e l l e r s h a f t a n d s h a f t c o u p l i n g s , c r a n k s h a f t a n d m a i n b e a r i n g s , t h r u s t b e a r i n g , f u e l t r e a t m e n t p l a n t , e x h a u s t v a l v e s a n d a c t u a t i o n , s t a r t i n g a i r s y s t e m , v i b r a t i o n m o n i t o r i n g s e n s o r s , c o n t r o l s y s t e m ( b a r r e d s p e e d r a n g e p r o g r a m m i n g )

Classification & regulatory

For 7-cylinder configuration, classification societies require detailed torsional vibration calculation and regular inspection of torsional vibration damper. Strictly observe IACS UR M68 (torsional vibrations). Compliance with barred speed ranges is prescribed by class. Document NOx emissions in accordance with MARPOL Annex VI. Observe torsional vibration damper replacement intervals according to manufacturer specification and class requirement. Observe tanker-specific requirements under SOLAS Chapter II-1 regarding machinery redundancy.

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

Other Cylinder Configurations 50

Components & Design

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Technical Data

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Manuals

operating
Sulzer RTA Operating Manual
Wärtsilä Switzerland (historical Sulzer)
maintenance
Sulzer RTA Maintenance Manual
Wärtsilä Switzerland (historical Sulzer)
spare_parts
Sulzer RTA Spare Parts Catalogue
Wärtsilä Switzerland (historical Sulzer)

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Equipment Model #38655 · ✓ still in production