Mitsubishi S6K Specifications
| Engine Model: Mitsubishi S6K |
| Engine Type: 4-cycle 6-cylinder SOHC forced-feed lubrication liquid-cooled diesel |
| Total Displacement: 388.9 cu.in (6.37 L) |
| Rated Engine Power: 109-161 Hp (81-120 kW) at 2000 rpm |
| Fuel System Type: Direct fuel injection |
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The Mitsubishi S6K is a substantial
six-cylinder diesel engine engineered for demanding heavy-duty
industrial and construction applications where robust power, high
torque, and unwavering reliability are paramount. This 6.373-liter power
plant is manufactured in both naturally aspirated (S6K) and turbocharged
(S6K-DT) configurations, providing a flexible power solution for a broad
spectrum of load requirements. Employing a direct injection combustion
system, it prioritizes thermodynamic efficiency, fuel economy, and
strong low-speed torque delivery.
The six-cylinder inline configuration delivers exceptional smoothness
due to inherent primary and secondary balance, minimizing vibration - a
critical feature for both operator comfort and the longevity of mounted
equipment. Constructed with a massively reinforced cast iron block and a
gear-driven valve train, the S6K series is designed for extended service
life under continuous high-load conditions, establishing itself as a
cornerstone power source for large excavators, heavy-duty generators,
and industrial machinery.
Manufacturer: Mitsubishi Heavy Industries, Ltd.
Engine Model: S6K (Naturally Aspirated), S6K-DT (Turbocharged).
Engine Type: 4-cycle, water-cooled, vertical inline, direct injection
diesel.
Aspiration: Naturally aspirated or Turbocharged (DT model).
The turbocharged variant may include an aftercooler.
Emission Compliance: Manufactured in variants conforming to various
regional standards, often corresponding to US EPA Tier 1/Tier 2 and
equivalent stages.
Management System: Mechanical fuel injection with mechanical governor.
Some later variants may incorporate basic electronic governing.
Number of Cylinders: 6.
Bore: 102 mm (4.016 in).
Stroke: 130 mm (5.118 in).
Displacement: 6.373 L (6373 cc) (388.9 cu in).
Compression Ratio: 17:1.
Firing Order: 1-5-3-6-2-4.
Rotation Direction: Counter-clockwise when viewed from the flywheel
side.
Maximum Gross Power Output (Naturally Aspirated): 81-89 kW (109-119 hp)
at 1,500-2,000 rpm for prime power applications.
Maximum Gross Power Output (Turbocharged S6K-DT): Up to 120 kW (161 hp)
at 2,000 rpm.
Maximum Gross Torque (Turbocharged): 590 Nm (435 lb-ft) at 1,400 rpm.
Rated Speed: 1,500-2,000 rpm, depending on application (industrial or
generator).
Idle Speed: 650-750 rpm.
The cylinder block is an immensely rigid, heavily ribbed casting
manufactured from high-strength gray iron. It employs a deep-skirt
design that extends far below the crankshaft centerline, creating an
exceptionally robust foundation that resists flexing and effectively
damps vibration. The cylinder bores are precision-honed and fitted with
replaceable dry-type cylinder liners constructed from wear-resistant
cast iron. This liner design facilitates overhaul and extends block
life. The crankshaft is a forged steel component, supported by seven
main bearings.
This seven-main-bearing support system is critical for maintaining
precise alignment and minimizing deflection of the long crankshaft under
extreme torque loads, ensuring smooth operation and durability.
Connecting rods are forged steel, fitted with replaceable precision
bearing shells at the crankpin end. Pistons are aluminum alloy with a
toroidal combustion bowl optimized for direct injection. Each piston is
cooled by dedicated jet nozzles spraying oil onto its underside. The
piston ring pack consists of two chrome-plated compression rings and a
three-piece oil control ring.
A single-piece cast iron cylinder head is utilized for each bank,
secured with multiple high-tensile studs and nuts per cylinder. The head
is designed to accommodate two intake and two exhaust valves per
cylinder (four-valve design) in many variants, optimizing airflow for
improved breathing and efficiency. Valve seat inserts are manufactured
from hardened, heat-resistant alloy.
The valve train is actuated by a single overhead camshaft (SOHC) per
head, driven by a gear train from the crankshaft. The camshaft operates
the valves via roller rocker arms, a design that reduces friction
losses. Valve clearance is adjusted by means of screw-type adjusters and
locknuts on the rocker arms, requiring periodic manual inspection and
setting.
The engine employs a mechanical, inline pump-line-nozzle fuel injection
system, engineered for the high pressures required for direct injection.
Core components include a mechanical fuel lift pump, a six-element
inline injection pump, high-pressure fuel lines, and multi-hole pintle
injectors. The injection pump is a large jerk-pump design, driven by the
engine's gear train. It supplies fuel at high pressure directly into the
main combustion chamber.
A mechanical centrifugal governor, integral to the injection pump,
regulates engine speed. The injection timing and fuel delivery curve are
mechanically calibrated. Fuel filtration is a multi-stage process,
involving a primary water-separating filter and a secondary fine filter,
both essential for protecting the precision injection components.
Lubrication is provided by a high-capacity, forced-feed, full-flow wet
sump system. A gear-type oil pump, driven directly from the crankshaft,
draws oil from the sump through a large pickup tube and screen.
Pressurized oil is routed through a full-flow, dual or large single
spin-on oil filter assembly.
After filtration, oil enters the main gallery, supplying the crankshaft
main and connecting rod bearings, the camshaft bearings, the valve
train, and the turbocharger (DT model). Dedicated piston cooling jets
are a critical component. The specified engine oil is API CF-4 or CG-4
grade. Total oil capacity is approximately 20 liters (21.1 US qt). The
oil pan is a heavy-duty stamped steel or cast iron component.
Cooling is managed by a high-capacity, pressurized, pump-circulated
liquid system. A centrifugal water pump, gear-driven from the front of
the engine, provides coolant circulation. System temperature is
regulated by a wax-pellet type thermostat. Heat rejection occurs via a
large tube-and-fin radiator; the cooling fan is V-belt or hydraulic
motor driven.
The turbocharged (DT) variant includes an air-to-air or air-to-water
aftercooler (ATAAC or ATAWC) for intake charge cooling. The cooling
system requires a 50/50 mixture of ethylene-glycol antifreeze and
deionized water. Total system capacity is 25 liters (26.4 US qt),
excluding machine-side radiators.
| Intake and Exhaust Systems |
Intake System: Consists of an air cleaner. The S6K-DT model adds a
turbocharger, intake piping, and an aftercooler. Exhaust System:
Comprises an exhaust manifold. On the turbocharged model, the manifold
feeds the turbocharger turbine, exiting via a downpipe.
Electrical System: Operates on a 24V system for starting. A 24V starter
motor and a 24V alternator are standard. A comprehensive sensor suite
(coolant temp, oil pressure) provides gauges and shutdown protection. An
electric stop solenoid acts on the injection pump rack.
Length (Front Face of Vibration Damper to Flywheel Housing): 1,185 mm
(46.65 in).
Width (Overall, at widest point): 740 mm (29.13 in).
Height (Overall, from sump to valve cover): 1,015 mm (39.96 in).
Dry Weight (turbocharged model with accessories): 475 kg (1,047 lb).
Engine Oil Change: Every 250 operating hours. Oil Filter Replacement:
Every oil change. Fuel Filter Replacement: Replace primary and secondary
filters every 500 hours. Air Cleaner Element Service: Clean or replace
based on restriction indicator; inspect daily in dusty environments.
Valve Clearance Adjustment: Check and adjust every 1,000 operating
hours.
Coolant Replacement: Drain, flush, and refill every 2,000 hours or two
years. Fan Belt Tension Check/Adjustment: Inspect and adjust every 500
hours. Fuel Injection System Inspection: Have injection pressure and
timing checked every 3,000 hours.
Cylinder Head Bolts: Tighten in a multi-step angular sequence: initial
torque to 110 Nm (81 lb-ft), followed by a final 90-degree turn.
Main Bearing Cap Bolts: 140 Nm (103 lb-ft) plus a 60-degree additional
turn.
Connecting Rod Cap Bolts: 120 Nm (89 lb-ft) plus a 60-degree turn.
Flywheel to Crankshaft Bolts: 200 Nm (148 lb-ft).
Fuel Injector Hold-down Clamp: 25 Nm (18 lb-ft).
Oil Pan Drain Plug: 59 Nm (44 lb-ft).
The Mitsubishi S6K engine is a prevalent power source in heavy-duty
machinery known for its durability and high torque. Hydraulic
Excavators: Komatsu PC200-3, PC200LC-3, PC220-3; Hitachi EX200;
Caterpillar 215, 225. Wheel Loaders: Medium to large wheel loaders from
various manufacturers. Generator Sets: Prime and standby power
generators in the 100-150 kVA range.
Industrial Pumps: Large-capacity water pumps for mining, irrigation, and
flood control. Compressors: Large industrial air compressors. Marine
Applications: Propulsion and auxiliary power for small ships, tugs, and
fishing vessels. Cranes: Mobile and crawler cranes in the 50-100 ton
capacity range.
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