Mitsubishi S6R Specifications
| Engine Model: Mitsubishi S6R |
| Engine Type: 4-cycle inline 6-cylinder turbocharged liquid-cooled diesel |
| Total Displacement: 1,495 cu.in (24.5 L) |
| Rated Engine Power: 603-925 Hp (450-690 kW) at 1800 rpm |
| Fuel System Type: Direct injection |
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The Mitsubishi S6R is a heavy-duty inline-six
diesel engine belonging to the Mitsubishi SR series engine family,
designed for continuous high-load operation in marine propulsion,
industrial power generation, and pumping applications. This powerplant
represents the largest displacement variant within the SR series,
engineered to deliver sustained power outputs from 450 kW (603 hp) to
690 kW (925 hp) for marine propulsion and generator set ratings from 600
kVA to 800 kVA. The S6R was developed to meet the demands of tugboats,
fishing vessels, landing craft, and stationary power installations where
reliability, fuel efficiency, and extended service intervals are
critical.
The engine’s architecture reflects Mitsubishi’s heavy-duty diesel
engineering philosophy, emphasizing robust construction and
field-serviceability. The cast iron cylinder block and cylinder head
provide the rigidity required for the elevated cylinder pressures
generated by turbocharged and aftercooled operation. The direct
injection fuel system with a mechanical inline pump delivers precise
fuel metering without electronic complexity.
The Mitsubishi S6R is offered in multiple configurations, including the
S6R-MPTK for marine propulsion and the S6R-PTA for industrial and
generator drive applications. The square bore and stroke dimensions -
170 mm x 180 mm - produce a displacement of 24.51 liters, favoring
torque production at moderate engine speeds of 1,600 rpm to 1,800 rpm.
The Mitsubishi S6R is a four-stroke, water-cooled, turbocharged diesel
engine configured with an intercooler or aftercooler depending on
application. The engine utilizes mechanical direct injection with an
inline injection pump.
Engine Type: Inline-6, 4-cycle, water-cooled diesel
Displacement: 24.51 L (24,510 cc / 1,495 cu.in)
Bore: 170.0 mm (6.69 in)
Stroke: 180.0 mm (7.09 in)
Compression Ratio: 14.0:1 to 14.5:1 depending on sub-model and
application
Firing Order: 1-5-3-6-2-4
Valvetrain: OHV (Overhead Valve), 12-valve (2 valves per cylinder)
Aspiration: Turbocharged with intercooler (aftercooler on select
variants)
Marine Propulsion Power: 450-690 kW (603-925 hp) at 1,600-1,800 rpm
Generator Drive Power: 600-800 kVA standby rating
Rated Speed: 1,600-1,800 rpm depending on application
Low Idle Speed: 450-550 rpm
Injection Timing: 16° to 22° before top dead center (pump-dependent)
The cylinder block is manufactured from high-strength cast iron using a
permanent mold casting process, selected for its dimensional stability,
wear resistance, and ability to withstand the elevated cylinder
pressures generated by turbocharged diesel operation. The block features
a deep-skirt design with the casting extending below the crankshaft
centerline, providing exceptional rigidity for the rotating assembly
under sustained high-load conditions.
The cylinder bores are machined directly into the iron casting or
utilize replaceable wet cylinder liners depending on the specific
variant. Wet liner construction permits liner replacement during
overhaul without reboring the block, reducing maintenance downtime and
costs. The block incorporates a siamesed bore configuration where
adjacent cylinders share common walls, increasing structural rigidity
and reducing overall engine length. Water jackets surround each cylinder
bore, with coolant flow directed from the water pump into the block
before rising into the cylinder head.
The crankcase incorporates seven main bearing supports with the bearing
webs integrated into the block casting. Main bearing caps are
manufactured from high-strength cast iron and secured with two bolts per
cap. The block includes mounting provisions for the inline injection
pump, gear-driven from the crankshaft, and the large-capacity oil filter
housing. A fabricated steel or cast aluminum oil pan is bolted to the
lower crankcase flange.
Crankshaft: Forged steel crankshaft with induction-hardened bearing
surfaces. Seven main bearings with steel-backed copper-lead bearing
shells. Connecting Rods: Forged steel connecting rods with a
conventional cap attachment using through-bolts. Pistons: Cast aluminum
alloy or steel pistons depending on variant. The piston crown
incorporates a re-entrant combustion bowl optimized for direct
injection.
Block Material: High-strength cast iron
Bore Diameter: 170.0 mm (6.69 in)
Cylinder Configuration: Inline, siamesed bores
Main Bearing Quantity: 7
Main Bearing Cap Design: Cast iron, two-bolt attachment
Cylinder Liner Type: Replaceable wet liner (most variants)
Balance Shafts: Not equipped
The cylinder head is constructed from cast iron using a permanent mold
casting process, selected for its thermal stability and compatibility
with the cast iron cylinder block in heavy-duty diesel applications. The
cross-flow port configuration places intake ports on one side and
exhaust ports on the opposite side. The OHV valvetrain operates 12
valves - two per cylinder - via pushrods and rocker arms.
The camshaft is located within the cylinder block and driven by a gear
train from the crankshaft. Camshaft lobes actuate mechanical lifters
(tappets) that translate motion upward through pushrods to the rocker
arms mounted on a rocker shaft. Valve clearance adjustment is performed
manually using a screw-and-locknut adjuster at the rocker arm. The
combustion chambers are of a direct injection design with a centrally
located bowl machined into the piston crown.
The cylinder head incorporates pressed-in valve seat inserts, with
exhaust seats manufactured from a nickel-based alloy. Valve guides are
pressed into the head. The valve seat angles are 30 degrees or 45
degrees depending on the variant. The cylinder head is secured to the
block using multiple head bolts per cylinder arranged in a specific
tightening sequence.
Head Material: Cast iron
Valve Configuration: OHV, 12-valve (2 valves per cylinder)
Intake Valve Diameter: 65.0-70.0 mm (2.56-2.76 in) depending on variant
Exhaust Valve Diameter: 55.0-60.0 mm (2.17-2.36 in) depending on variant
Valve Stem Diameter: 12.0 mm (0.47 in)
Valve Seat Angle: 30° or 45° depending on variant
Camshaft Drive: Gear train from crankshaft
Valve Clearance (Cold, Intake): 0.40 mm (0.016 in)
Valve Clearance (Cold, Exhaust): 0.50 mm (0.020 in)
Interference Engine: No - valve-to-piston clearance maintained
The fuel system is a mechanically controlled direct injection design
utilizing an inline injection pump. The pump is a Bosch or Zexel inline
jerk-type pump with a mechanical or electronic governor depending on
variant, mounted on the side of the cylinder block and driven by a gear
train from the crankshaft.
The governor provides isochronous or droop speed control depending on
application. Generator drive variants require isochronous governors for
precise frequency regulation. A mechanical lift pump or electric priming
pump draws fuel from the tank through a primary water-separating filter
and delivers it to the injection pump. A secondary spin-on fuel filter
is mounted between the lift pump and the injection pump.
The injectors are of the multi-hole nozzle type, calibrated to open at
pressures between 20,000 kPa and 25,000 kPa (2,900-3,625 psi). Each
injector is retained in the cylinder head by a clamp. Injection timing
is set between 16° and 22° before top dead center depending on the
specific fuel pump and engine configuration.
Injection Type: Direct injection, mechanical inline jerk pump
Injection Pump Type: Inline 6-cylinder, mechanical or electronic
governor
Injector Opening Pressure: 20.0-25.0 MPa (2,900-3,625 psi)
Injection Timing: 16°-22° BTDC (pump-dependent)
Fuel Filtration: Primary water-separating filter plus secondary spin-on
filter
Fuel Requirement: Diesel fuel meeting ASTM D975 or EN 590; minimum
cetane 45
The lubrication system is a fully pressurized, wet-sump design with a
gear-type oil pump mounted internally within the timing gear case and
driven by the crankshaft. The oil pump utilizes a pair of meshing gears
to generate flow with positive displacement characteristics. The
lubrication system capacity is substantial to support extended operation
in marine and industrial applications.
Oil is drawn from the fabricated steel or cast aluminum oil pan through
a mesh strainer positioned at the sump’s lowest point. Pressurized oil
passes through a full-flow, replaceable oil filter mounted externally on
the cylinder block. The filter incorporates a bypass valve that permits
oil flow to continue if the filter element becomes restricted. From the
filter, oil enters the main oil gallery cast longitudinally through the
cylinder block, supplying the crankshaft main bearings, connecting rod
bearings, camshaft bearings, rocker arm assemblies, and turbocharger
bearings.
A pressure relief valve bypasses excess oil flow back to the oil pan
when system pressure exceeds the calibrated limit. An oil pressure gauge
sender provides analog pressure indication at the helm or control panel.
The lubrication system includes an oil cooler - a water-to-oil heat
exchanger - to maintain lubricant temperature under sustained high-load
operation.
Oil Type: Diesel engine oil meeting API CD, CE, or CF; SAE 30 or 40
viscosity
Oil Capacity: 80-100 L (21-26 US gal) depending on oil pan type
Oil Pressure (at idle, warm): 150-250 kPa (22-36 psi)
Oil Pressure (at rated speed): 400-600 kPa (58-87 psi)
Oil Pump Type: Gear-type, crankshaft-driven
Oil Cooler: Water-to-oil heat exchanger
The cooling system is a pressurized, liquid-cooled design with a
belt-driven or gear-driven centrifugal water pump mounted on the front
of the cylinder block. The water pump impeller circulates coolant
through the cylinder block water jackets, cylinder head passages, oil
cooler, aftercooler (where fitted), and radiator or keel cooler
depending on installation.
A wax-pellet thermostat mounted in a housing on the cylinder head outlet
regulates coolant flow to the radiator or heat exchanger. The thermostat
begins opening at a calibrated temperature and achieves full opening
within a defined temperature range. A bypass circuit permits coolant
circulation within the engine during warm-up.
Marine installations utilize either a keel cooler (coolant circulated
through pipes mounted on the vessel’s hull) or a heat exchanger with a
seawater circuit. Stationary power installations use a radiator with an
engine-driven or electric fan. The cooling system incorporates an
expansion tank with a pressure-rated cap.
Coolant Type: Ethylene-glycol based antifreeze meeting Mitsubishi
specification
Coolant Capacity (engine only): 40-60 L (10.6-15.9 US gal) depending on
configuration
Thermostat Opening Temperature: 76-82 °C (169-180 °F)
Thermostat Full Opening Temperature: 90-95 °C (194-203 °F)
Radiator Cap Pressure: 70-100 kPa (10-15 psi)
Water Pump Type: Centrifugal, belt-driven or gear-driven
| Intake and Exhaust Systems |
Intake System: The intake system incorporates a dry-type paper-element
air cleaner with a restriction indicator. Filtered air enters the
turbocharger compressor, then passes through an intercooler (air-to-air)
or aftercooler (air-to-water) before entering the intake manifold. The
aftercooler reduces intake air temperature, improving volumetric
efficiency and reducing exhaust emissions.
Exhaust System: The exhaust manifold is a cast iron single-piece design
collecting exhaust gases from all six cylinders. The turbocharger
discharges into a water-cooled exhaust elbow on marine installations or
a dry exhaust stack on stationary applications. Marine configurations
inject cooling water into the exhaust stream before discharge overboard.
Governor: Mechanical or electronic governor depending on variant.
Electronic governors provide isochronous speed control for generator
sets, maintaining frequency within ±0.25% under varying loads.
Mechanical governors utilize flyweights and spring mechanisms for speed
sensing and fuel rack control.
Starting System: The engine is equipped with a 24-volt electric starting
system. A gear-reduction starter motor engages with the flywheel ring
gear. An air starting system is available as an option for applications
where large starting batteries are impractical. Glow plugs or intake air
grid heaters provide cold-start assistance.
Turbocharger: Single or twin turbochargers depending on power rating.
Turbochargers are water-cooled on marine configurations to prevent
coking of lubricating oil during low-load operation.
Timing Drive: The camshaft, injection pump, and accessory drives are
driven by a gear train from the crankshaft. This gear-driven system
requires no periodic replacement and provides precise synchronization
throughout the engine’s service life.
Overall Length: 2,500 mm (98.4 in)
Overall Width: 1,300 mm (51.2 in)
Overall Height: 1,800 mm (70.9 in)
Dry Weight (engine only): 2,650-2,950 kg (5,842-6,504 lb)
Engine Oil Change: 250-500 operating hours depending on oil analysis.
Engine Oil Filter Change: At every oil change.
Fuel Filter Replacement: 500 operating hours or annually.
Air Filter Element Replacement: When restriction indicator shows or
1,000 hours.
Coolant Replacement: 2,000 operating hours or 2 years.
Valve Clearance Inspection: 500 operating hours; adjust as required.
Injector Service: 1,000-1,500 operating hours inspection and
calibration.
Injection Pump Timing: Inspect following any pump removal or drive gear
disturbance.
Drive Belt (Accessory) Inspection: 250 operating hours.
Turbocharger Inspection: 2,000 operating hours.
Oil Analysis: Recommended every 250 operating hours for condition
monitoring.
Cylinder Head Bolts, 1st pass: 200-250 Nm (148-184 lb-ft)
Cylinder Head Bolts, Final pass: 490-539 Nm (361-398 lb-ft)
Main Bearing Cap Bolts, 1st pass: 300-350 Nm (221-258 lb-ft)
Main Bearing Cap Bolts, Final pass: 686-735 Nm (506-542 lb-ft)
Connecting Rod Cap Bolts, 1st pass: 200-250 Nm (148-184 lb-ft)
Connecting Rod Cap Bolts, Final pass: 441-490 Nm (325-361 lb-ft)
Flywheel Bolts: 441-490 Nm (325-361 lb-ft)
Crankshaft Pulley Bolt: 1,000-1,200 Nm (738-885 lb-ft)
Rocker Arm Shaft Bolts: 100-120 Nm (74-89 lb-ft)
Intake Manifold Bolts: 50-60 Nm (37-44 lb-ft)
Exhaust Manifold Nuts: 60-70 Nm (44-52 lb-ft)
Injection Pump Mounting Nuts: 50-60 Nm (37-44 lb-ft)
Fuel Injector Holders: 120-150 Nm (89-111 lb-ft)
High-Pressure Fuel Line Fittings: 30-35 Nm (22-26 lb-ft)
Oil Pan Bolts: 40-50 Nm (30-37 lb-ft)
Water Pump Bolts: 50-60 Nm (37-44 lb-ft)
Thermostat Housing Bolts: 30-35 Nm (22-26 lb-ft)
The Mitsubishi S6R engine was deployed across marine propulsion,
industrial power generation, and pumping applications.
Marine Propulsion:
Tugboats: The S6R-MPTK is installed in harbor and coastal tugboats
requiring sustained bollard pull. The engine’s torque characteristics
suit the variable load conditions of pushing and towing operations.
Fishing Vessels: Trawlers, seiners, and longliners utilize the S6R for
main propulsion, where fuel efficiency and reliability are critical for
extended voyages.
Landing Craft and Workboats: Military and commercial landing craft, crew
transfer vessels, and supply boats receive the S6R as a propulsion
engine.
Generator Sets:
Standby Power: The S6R-PTA is installed in generator sets for standby
power at data centers, hospitals, and industrial facilities, providing
600-800 kVA ratings.
Prime Power: Continuous power generation for remote communities, mining
operations, and construction sites without grid access.
Industrial Pumping:
Irrigation and Flood Control: Large-capacity water pumps for
agricultural irrigation and flood control systems use the S6R as a power
unit.
Fire Pump Systems: Stationary fire protection systems requiring reliable
starting and sustained operation under emergency conditions.
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