Mitsubishi S4S-DT Specifications
| Engine Model: Mitsubishi S4S-DT |
| Engine Type: 4-cycle inline 4-cylinder turbocharged liquid-cooled diesel |
| Total Displacement: 203.3 cu.in (3.33 L) |
| Rated Engine Power: 83 Hp (62 kW) at 2500 rpm |
| Fuel System Type: Direct fuel injection |
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The Mitsubishi S4S-DT is a turbocharged, direct
injection evolution of the established S4S diesel engine platform,
engineered to deliver increased power density and torque output for
demanding industrial applications. This 3.331-liter, four-cylinder power
plant retains the robust mechanical architecture of its predecessor
while incorporating forced induction and a direct injection combustion
system to achieve a substantial rise in performance.
The integration of a turbocharger significantly improves volumetric
efficiency, resulting in higher power and a more pronounced torque
curve, making it well-suited for equipment requiring strong low-speed
response, such as heavy-duty forklifts, large generator sets, and
industrial pumps. The direct injection system contributes to enhanced
fuel economy and thermal efficiency compared to the indirect injection
S4S model. The engine's construction maintains an emphasis on durability
and serviceability, with a heavy-duty cast iron block and a gear-driven
valvetrain, ensuring reliable operation in continuous-use and high-load
environments.
Manufacturer: Mitsubishi Heavy Industries Engine and Turbocharger, Ltd.
(MHIET).
Engine Model: S4S-DT.
Engine Type: 4-cycle, water-cooled, vertical inline, direct injection,
turbocharged diesel.
Aspiration: Turbocharged. An air-to-air or air-to-water aftercooler may
be present on specific high-output variants.
Management System: Mechanical fuel injection with mechanical governor.
Number of Cylinders: 4.
Bore: 94 mm (3.701 in).
Stroke: 120 mm (4.724 in).
Displacement: 3.331 L (3331 cc) (203.3 cu in).
Compression Ratio: 17:1.
Firing Order: 1-3-4-2.
Rotation Direction: Counter-clockwise when viewed from the flywheel
side.
Maximum Gross Power Output: 62 kW (83 hp) at 2,500 rpm.
Maximum Gross Torque: 245 Nm (181 lb-ft) at 1,600 rpm.
Rated Speed: 2,500 rpm for variable-speed applications; 1,500 or 1,800
rpm for constant-speed generator duty.
Idle Speed: 650-750 rpm.
Emission Compliance: Manufactured in configurations meeting various
historical and regional industrial engine standards, often corresponding
to older emission tiers (e.g., EPA Tier 1/Tier 2, EU Stage I/II).
The cylinder block is a substantial, heavily ribbed casting manufactured
from high-strength gray iron. It employs a deep-skirt design that
extends well below the crankshaft centerline, contributing decisively to
overall structural rigidity and reducing vibration and noise emissions.
The cylinder bores are precision-honed directly into the block material,
a linerless construction that provides efficient heat transfer from the
cylinder walls to the surrounding coolant jackets.
The crankshaft is a forged steel component, supported by five main
bearings. This five-bearing support system is essential for maintaining
crankshaft alignment and stability under the increased cylinder
pressures generated by turbocharging. Connecting rods are forged steel,
fitted with replaceable precision bearing shells at the crankpin end.
The piston pin is a press-fit in the connecting rod small end.
Pistons are aluminum alloy, designed with a specific re-entrant
combustion bowl engineered to generate intense air swirl for optimal
air-fuel mixing in the direct injection environment. 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 employed, secured to the block
with high-tensile studs and nuts. The head is designed to accommodate
one intake and one exhaust valve per cylinder. Valve seat inserts are
manufactured from hardened, heat-resistant alloy to withstand the
elevated temperatures associated with turbocharged operation. The valve
train operates on an overhead valve (OHV) principle, with the camshaft
positioned in the cylinder block.
The camshaft is gear-driven from the crankshaft, providing positive
timing without reliance on a belt or chain. The camshaft actuates the
valves via solid pushrods and rocker arms. Rocker arms are mounted on a
stationary shaft fastened to the cylinder head. Valve clearance is set
and maintained by a screw and locknut adjustment on each rocker arm, a
fundamental and regular maintenance procedure. The cylinder head for the
DT model is configured for direct injection, with the fuel injector
mounted centrally.
The engine employs a mechanical, inline pump-line-nozzle fuel injection
system, calibrated for the higher pressures required for direct
injection. Core components include a mechanical fuel lift pump, an
inline injection pump with individual pumping elements for each
cylinder, high-pressure fuel lines, and multi-hole pintle injectors. The
injection pump is a jerk-pump design, driven by the engine's gear train.
It supplies fuel at elevated pressure directly into the main combustion
chamber within the piston bowl.
A mechanical centrifugal governor, integral to the injection pump,
regulates engine speed by controlling the position of the fuel rack. The
injection timing and fuel delivery curve are mechanically set to
optimize performance and emissions for the turbocharged application.
Fuel filtration is a critical two-stage process, involving a primary
sedimentor/water separator and a secondary fine filter.
Lubrication is provided by a forced-feed, full-flow wet sump system. A
gear-type oil pump, driven directly from the crankshaft, draws oil from
the sump through a pickup tube equipped with a robust strainer screen.
Pressurized oil is routed through a full-flow, spin-on cartridge oil
filter.
After filtration, oil enters the main oil gallery in the block,
supplying the crankshaft main and connecting rod bearings, the camshaft
bearings, the valve gear via internal passages and hollow pushrods, and
the turbocharger center bearing through a dedicated feed line. An oil
drain line returns oil from the turbocharger to the sump. The specified
engine oil is API CD or CF grade. Total oil capacity, including the
filter, is 10.0 liters (10.6 US qt). The oil pan is a heavy-duty stamped
steel or cast iron component.
Cooling is managed by a pressurized, pump-circulated liquid system. A
centrifugal water pump, driven by a V-belt from the crankshaft pulley,
provides coolant circulation. System operating temperature is regulated
by a wax-pellet type thermostat. Heat rejection occurs via a
tube-and-fin radiator; the cooling fan is mounted on the engine and is
V-belt driven.
The increased thermal load from turbocharging necessitates a
high-capacity cooling system. The cooling system requires a mixture of
ethylene-glycol antifreeze and clean, deionized water, generally in a
50/50 ratio. Total cooling system capacity is 10.0 liters (10.6 US qt)
for the engine side, excluding the radiator and external hose volume.
| Intake and Exhaust Systems |
Intake System: Consists of an air cleaner, turbocharger, and intake
piping. Some variants may include an aftercooler. Exhaust System:
Comprises an exhaust manifold that routes gas to the turbocharger
turbine housing. After exiting the turbocharger, exhaust flows through a
downpipe to the machine's exhaust silencer.
Electrical System: Operates on a 12V or 24V system, with 24V being
common for industrial applications. A corresponding starter motor and
alternator are fitted. A glow plug system is retained for cold starting
assistance. An electric stop solenoid acts on the injection pump rack.
Length (Front Face of Block to Flywheel Housing): 780 mm (30.71 in).
Width (Overall, including turbocharger and manifolds): 595 mm (23.43
in).
Height (Overall, from sump to valve cover): 820 mm (32.28 in).
Dry Weight (with standard accessories and turbocharger): 250 kg (551
lb).
Engine Oil Change: Every 250 operating hours. Oil Filter Replacement:
Every oil change (250 hours). Fuel Filter Replacement: Replace primary
and secondary filter elements every 500 operating hours. Air Cleaner
Element Service: Clean or replace based on restriction indicator;
inspect very frequently due to turbocharger sensitivity to dust. Valve
Clearance Adjustment: Check and adjust every 500 operating hours.
Coolant Replacement: Drain, flush, and refill every 2,000 operating
hours or every two years. Fan Belt Tension Check/Adjustment: Inspect and
adjust tension every 250 hours. Turbocharger Inspection: Check for axial
and radial play, and oil leakage, every 1,000 hours.
Cylinder Head Nuts: Tighten in the specified multi-step crisscross
sequence to a final torque of 137-147 Nm (101-108 lb-ft). Main Bearing
Cap Bolts: 118-127 Nm (87-94 lb-ft).
Connecting Rod Cap Bolts: 78-88 Nm (58-65 lb-ft).
Flywheel to Crankshaft Bolts: 137-147 Nm (101-108 lb-ft).
Fuel Injector Holder: 69-78 Nm (51-58 lb-ft).
Turbocharger Mounting Nuts/Bolts: 39-49 Nm (29-36 lb-ft).
Oil Pan Drain Plug: 59-69 Nm (44-51 lb-ft).
Oil Filter Cartridge: Hand-tighten plus 3/4 turn after gasket contact.
The Mitsubishi S4S-DT engine is deployed in heavy-duty industrial
equipment where the combination of turbocharged power and direct
injection efficiency is required. Common applications include:
Heavy-Duty Forklifts: Powers large container handlers, and forklifts in
the 8 to 15 ton capacity range. Generator Sets: A prime mover for
industrial and prime power generator sets in the 50-75 kVA power range.
Industrial Pumps: Drives high-pressure and high-volume pumps for
firefighting, oil and gas, and major irrigation projects. Compressors:
Used as the diesel driver for large industrial screw-type and
reciprocating air compressors. Construction Equipment: Powers larger
vibratory rollers, drilling rigs, and stationary crushers or screeners.
Marine Applications: Serves as a propulsion engine for small tugs,
workboats, and fishing vessels, and as a generator drive on larger
vessels.
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