Mitsubishi S4K-T Specifications
| Engine Model: Mitsubishi S4K-T |
| Engine Type: 4-cycle inline 4-cylinder turbocharged liquid-cooled diesel |
| Total Displacement: 259.3 cu.in (4.25 L) |
| Rated Engine Power: 93-106 Hp (70-79 kW) at 2200 rpm |
| Fuel System Type: Direct injection |
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The Mitsubishi S4KT is a 4-cylinder,
turbocharged, direct-injection diesel engine from the S4K series.
Developed as a high-performance variant specifically engineered for
heavy construction machinery, industrial equipment, and power generation
applications, this engine combines a robust cast iron construction with
forced induction to deliver increased power output within a compact
displacement.
The S4K-T is widely recognized for its durability under sustained
high-load conditions, serving in excavators, generator sets, forklifts,
and wheel loaders across global markets. The "T" designation indicates
turbocharged aspiration, distinguishing it from naturally aspirated S4K
variants.
The Mitsubishi S4KT represents a purpose-built industrial diesel
architecture prioritizing torque characteristics suitable for
construction and power generation duty cycles. Its inline 4-cylinder
configuration with a long stroke of 130 mm provides favorable low-speed
torque output, essential for excavator digging operations and generator
load acceptance. The cast iron cylinder block with a parent-bore design
offers durability without the complexity of replaceable liners.
The overhead valve (OHV) valvetrain with eight valves provides a simple,
serviceable layout accessible for valve lash adjustment. The direct
injection combustion system, combined with a turbocharger, delivers
improved thermal efficiency and reduced fuel consumption compared to
naturally aspirated indirect injection designs. The mechanical fuel
injection system operates without electronic controls, simplifying field
repairs in remote construction sites.
Engine Type: Inline 4-cylinder, 4-cycle, water-cooled, turbocharged
diesel
Family: Mitsubishi S4K Series
Displacement: 4.249 liters (4,249 cc / 259.3 cu.in)
Bore x Stroke: 102.0 mm x 130.0 mm (4.02 in x 5.12 in)
Compression Ratio: 17:1
Firing Order: 1-3-4-2
Aspiration: Turbocharged
Maximum Power (S4K-T / Industrial): 70 kW (93 hp) at 1950 rpm
Maximum Power (S4K-T / Generator): 79.0 kW (106 hp) at 2200 rpm
Maximum Torque: 380-420 Nm (280-310 lb-ft) @ 1,400-1,600 rpm
Idle Speed (Low): 650-700 rpm
Valvetrain: OHV, 8 valves (2 valves per cylinder).
Mechanical pushrods and rocker arms.
Direct injection combustion system.
The cylinder block is constructed from cast iron with a deep-skirt
design, providing structural rigidity required for sustained high-load
industrial operation. The block utilizes a parent-bore design with
cylinder bores machined directly into the cast iron casting, eliminating
replaceable liners. The cylinder bores are induction-hardened to resist
wear under extended service intervals.
Five main bearings support the crankshaft. The water jacket surrounds
each cylinder with cast-in coolant passages optimized for uniform
thermal distribution. The camshaft is located within the cylinder block
on the right-hand side, driven by a gear train from the crankshaft. The
engine mounting points are positioned on the sides and front of the
block, accommodating various industrial equipment configurations.
The cylinder head is manufactured from cast iron, selected for thermal
stability and resistance to distortion under turbocharged diesel
combustion pressures. It employs an OHV configuration with the camshaft
located within the cylinder block. The eight valves are arranged with
two valves per cylinder in a vertical orientation. Valve actuation is
achieved via mechanical pushrods and rocker arms, with screw-and-locknut
adjusters for valve lash setting.
The combustion system utilizes direct injection with a re-entrant bowl
machined into the piston crown. The cylinder head incorporates separate
intake and exhaust ports on opposite sides. The exhaust manifold is
designed to mount the turbocharger. Valve seats are induction-hardened,
with valve guides manufactured from cast iron.
The engine is equipped with a mechanical direct injection fuel system.
An in-line injection pump, manufactured by Bosch or Zexel depending on
production date, is mounted to the side of the cylinder block, driven by
a gear from the camshaft. The injection pump incorporates a mechanical
governor, providing speed control and load response for industrial and
generator applications.
The governor includes idle and maximum speed spring sets, with
adjustable droop characteristics for generator load acceptance.
Injection timing is adjustable via shims between the pump mounting
flange and the block. Each cylinder receives fuel from a nozzle-type
injector, with injector opening pressure calibrated to 150-160 bar
(2,175-2,320 psi). A fuel supply pump draws fuel through a primary
filter and water separator assembly.
The lubrication system is a pressurized, wet-sump configuration designed
for extended service intervals in dusty industrial environments. A
gear-type oil pump, driven by the crankshaft, draws oil from the sump
and circulates it through a full-flow disposable spin-on filter. An
optional oil cooler may be fitted for high-ambient-temperature
applications.
Oil galleries within the block and cylinder head supply pressurized oil
to the five main bearings, connecting rod bearings, camshaft bearings,
rocker arm assemblies, and turbocharger bearing housing. The
turbocharger receives oil through a dedicated supply line with a
restrictor fitting. A pressure relief valve maintains system pressure.
Total oil capacity ranges from 13.0 to 18.5 liters (13.7 to 19.5 qt),
depending on oil pan depth and application.
The cooling system is a pressurized, water-cooled design with forced
circulation. A belt-driven centrifugal water pump, mounted to the front
of the cylinder block, circulates coolant through the cylinder block,
cylinder head, turbocharger, and radiator. A wax-type thermostat,
beginning to open at 71-76°C (160-169°F), regulates coolant flow to
maintain optimal operating temperatures.
This lower thermostat opening temperature is specified for sustained
high-load industrial operation. The system utilizes a cross-flow
radiator with a mechanical or electric cooling fan depending on the
equipment application. Coolant capacity varies by radiator size and
equipment configuration.
Glow Plug System: The engine is equipped with glow plugs for cold-start
assistance. One glow plug per cylinder is installed in the cylinder
head, controlled by a glow control unit or manual push-button circuit.
Timing System: The camshaft and injection pump are driven by a gear
train housed at the front of the engine. The crankshaft gear drives an
idler gear, which in turn drives the camshaft gear and injection pump
gear. This gear-driven arrangement eliminates timing belt or chain
replacement requirements.
Governor System: The mechanical governor integrated into the injection
pump includes both low-idle and high-speed control functions. For
generator applications, the governor is calibrated for isochronous or
droop operation as specified.
Turbocharger System: A fixed-geometry turbocharger provides forced
induction. The turbocharger is mounted to the exhaust manifold, with
boost pressure regulated by a wastegate actuator on certain variants.
Emission Control: The engine incorporates a positive crankcase
ventilation (PCV) system. No catalytic converter or exhaust gas
recirculation system is present on standard S4KT configurations.
Electrical System: The charging system consists of a 12-volt or 24-volt
alternator, depending on application requirements. The starter motor is
sized for diesel cranking requirements.
Dry Weight (Engine Only): 380 kg (838 lb)
Dry Weight (with Flywheel and Bellhousing): 420 kg (926 lb)
Overall Length (from front pulley to flywheel housing): 950 mm (37.4 in)
Overall Width: 600 mm (23.6 in)
Overall Height: 950 mm (37.4 in)
Bore Pitch: 118 mm (4.65 in)
Engine Oil Capacity: 13.0-18.5 liters (13.7-19.5 qt), depending on oil
pan configuration.
Engine Oil Specification: SAE 15W-40 or 10W-30, API CD, CE, CF, or
higher.
Engine Oil Pressure (at idle): Minimum 1.0 bar (15 psi).
Engine Oil Pressure (at rated speed): 3.0-5.0 bar (44-73 psi).
Coolant Capacity: Variable by application; engine only 7.0 liters (7.4
qt).
Coolant Specification: Ethylene glycol-based antifreeze with corrosion
inhibitors.
Valve Clearance (Cold): Intake: 0.25 mm (0.010 in). Exhaust: 0.25 mm
(0.010 in).
Valve Clearance Inspection Interval: Every 500 operating hours.
Fuel Injection Timing: 20° before top dead center (BTDC) at injection
pump installation.
Injector Opening Pressure: 150-160 bar (2,175-2,320 psi).
Oil Change Interval: 250-500 operating hours, depending on duty cycle
and oil quality.
Fuel Filter Replacement Interval: 250 operating hours.
Idle Speed (Low): 650-700 rpm
High Idle No-Load Speed: 2,050-2,100 rpm for generator applications.
High Idle No-Load Speed: 2,300-2,350 rpm for industrial equipment.
Compression Pressure: Standard: 28-32 bar (406-464 psi) at cranking
speed.
Cylinder Head Bolts (M12, Large), Stage 1: 60 Nm (44 lb-ft)
Cylinder Head Bolts (M12, Large), Stage 2: 100 Nm (74 lb-ft)
Cylinder Head Bolts (M12, Large), Stage 3: 118-127 Nm (87-94 lb-ft)
Cylinder Head Bolts (M10, Small): 78-88 Nm (58-65 lb-ft)
Main Bearing Cap Bolts: 120-130 Nm (89-96 lb-ft)
Connecting Rod Cap Bolts: 49-54 Nm (36-40 lb-ft)
Camshaft Bearing Cap Bolts: 20-25 Nm (15-18 lb-ft)
Flywheel Bolts: 90-100 Nm (66-74 lb-ft)
Crankshaft Pulley Bolt: 250-300 Nm (184-221 lb-ft)
Intake Manifold Nuts: 25-30 Nm (18-22 lb-ft)
Exhaust Manifold Nuts: 30-35 Nm (22-26 lb-ft)
Injector Hold-Down Clamp Bolts: 20-25 Nm (15-18 lb-ft)
Glow Plugs: 15-20 Nm (11-15 lb-ft)
Rocker Arm Shaft Bracket Bolts: 25-30 Nm (18-22 lb-ft)
Valve Cover Bolts: 8-10 Nm (6-7 lb-ft)
Oil Pan Bolts: 15-20 Nm (11-15 lb-ft)
Oil Pump Mounting Bolts: 25-30 Nm (18-22 lb-ft)
Water Pump Mounting Bolts: 20-25 Nm (15-18 lb-ft)
Turbocharger Mounting Nuts: 35-40 Nm (26-30 lb-ft)
Injection Pump Mounting Nuts: 30-35 Nm (22-26 lb-ft)
Engine Mount (Bracket to Block): 50-60 Nm (37-44 lb-ft)
The Mitsubishi S4KT engine was utilized across a range of heavy
construction machinery, industrial equipment, and power generation
applications.
Hydraulic Excavators: The S4K-T powered excavator models including the
Caterpillar 312 (as OEM supply), Mitsubishi MS120, MS140, and various
other 12-15 tonne class excavators requiring turbocharged diesel
performance for digging and lifting operations.
Crawler Excavators: Komatsu and Caterpillar excavator variants in the
10-14 tonne range received the S4KT as an original equipment or
replacement powerplant.
Generator Sets (30-50 kVA): The engine served in prime and standby power
generation units, providing reliable power at 1,500 rpm (50 Hz) or 1,800
rpm (60 Hz) configurations.
Industrial Forklifts: TCM and Mitsubishi-branded forklifts in the 7-10
tonne capacity class utilized the S4K-T for heavy material handling
applications requiring sustained high-torque output.
Wheel Loaders: Compact wheel loaders and skid-steer loader variants
received the S4KT engine for construction material handling and site
preparation duties.
Heavy-Duty Pumps: Stationary pump installations including irrigation
pumps, dewatering pumps, and fire suppression systems utilized the S4KT
as a prime mover for continuous-duty applications.
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