Mitsubishi S4S Specifications
| Engine Model: Mitsubishi S4S |
| Engine Type: 4-cycle inline 4-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 203.3 cu.in (3.33 L) |
| Rated Engine Power: 63 Hp (47 kW) at 2500 rpm |
| Fuel System Type: Indirect fuel injection |
____________________________________________________________________________________
The Mitsubishi S4S is a robust,
medium-displacement four-cylinder diesel engine engineered for
dependable performance across a broad spectrum of industrial and
agricultural applications. This 3.3-liter power plant is characterized
by a straightforward, naturally aspirated design and an indirect
injection combustion system, prioritizing mechanical reliability,
operational smoothness, and ease of maintenance over peak power density.
Its substantial torque output, delivered at low to medium engine speeds,
makes it well-suited for equipment subjected to heavy cyclical loads,
such as forklifts, agricultural tractors, and hydraulic excavators. The
engine's construction emphasizes durability, with a heavy-duty cast iron
block and a gear-driven camshaft ensuring longevity in demanding work
environments. The S4S provides a proven and cost-effective power
solution where absolute maximum power is secondary to consistent torque
delivery, fuel economy, and extended service intervals.
Manufacturer: Mitsubishi Heavy Industries Engine and Turbocharger, Ltd.
(MHIET).
Engine Model: S4S.
Engine Type: 4-cycle, water-cooled, vertical inline, indirect injection
diesel.
Aspiration: Naturally aspirated.
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: 22:1.
Firing Order: 1-3-4-2.
Rotation Direction: Counter-clockwise when viewed from the flywheel
side.
Maximum Gross Power Output: 47 kW (63 hp) at 2,500 rpm.
Maximum Gross Torque: 182 Nm (134 lb-ft) at 1,600 rpm (representative
value; specific applications may vary). Rated Speed Range: 1,500 rpm
(generators) to 2,300 rpm (industrial).
Idle Speed: 650-750 rpm.
Emission Compliance: Manufactured in configurations meeting various
historical and regional industrial engine standards (e.g., Japanese
Industrial Standards, earlier EU directives).
The cylinder block is a substantial, heavily ribbed casting manufactured
from high-strength gray iron. It features a deep-skirt design that
extends well below the crankshaft centerline, contributing significantly
to overall structural rigidity and reducing vibration. The cylinder
bores are precision-honed directly into the block material, utilizing a
linerless construction that provides effective heat dissipation to the
surrounding coolant jackets.
The crankshaft is a forged steel component, supported by five generously
sized main bearings. This five-bearing support system guarantees
exceptional crankshaft stability under high torque loads, minimizing
deflection and contributing to extended bearing life. 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 crown profile
compatible with the indirect injection swirl chamber system. 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 ensure longevity
under continuous thermal stress. 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 and eliminating the need for a timing 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 maintenance procedure. The
cylinder head incorporates the indirect injection pre-combustion (swirl)
chamber for each cylinder, which houses a glow plug for cold starting
assistance.
The engine employs a mechanical, inline pump-line-nozzle fuel injection
system. Core components include a mechanical fuel lift pump, an inline
injection pump with individual pumping elements for each cylinder,
high-pressure fuel lines, and injectors. The injection pump is a
jerk-pump design, driven by the engine's gear train. It supplies fuel at
high pressure to pintle-type nozzles that discharge into the
pre-combustion swirl chamber.
A mechanical centrifugal governor, integral to the injection pump,
regulates engine speed by controlling the position of the fuel rack. The
system is calibrated for consistent fuel delivery across the operating
range, contributing to the engine's stable torque curve. Fuel filtration
is a two-stage process, involving a primary sedimentor/water separator
and a secondary fine filter to protect the precision components of the
injection pump and injectors from contamination.
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, and the valve gear via internal passages and hollow pushrods.
The system is designed for high flow and pressure to ensure adequate
lubrication and cooling of internal components. 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 housed in the water outlet housing. Heat
rejection occurs via a tube-and-fin radiator; the cooling fan is mounted
on the engine and is V-belt driven.
The substantial displacement and thermal load of the engine necessitate
an effective cooling system. The cooling system requires a mixture of
ethylene-glycol antifreeze and clean, deionized water. A 50/50 mixture
is standard for full corrosion protection and freeze resistance. Total
cooling system capacity is 9.0 liters (9.5 US qt) for the engine side,
excluding the radiator and external hose volume.
Intake System: Consists of an air cleaner and a simple intake manifold.
The naturally aspirated design eliminates the need for
turbocharger-related components. Exhaust System: Comprises a cast iron
exhaust manifold and a downpipe connecting to the machine's exhaust
silencer.
Electrical System: Operates on a 12V system. A 12V, 2.2 kW starter motor
and a 12V alternator (commonly 35-50A) are standard. The engine
incorporates a glow plug system for each cylinder, controlled by a
key-switch or timer module for cold starting. An electric stop solenoid
acts on the injection pump rack.
Governor: A mechanical centrifugal governor is standard, integrated
within the fuel injection pump. For constant-speed applications like
generators, an isochronous governor may be fitted.
Length (Front Face of Block to Flywheel Housing): 780 mm (30.71 in).
Width (Overall): 560 mm (22.05 in).
Height (Overall, from sump to valve cover): 715 mm (28.15 in).
Dry Weight (with standard accessories): 245 kg (540 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 daily in dusty agricultural or construction environments. 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; replace belts showing signs of wear,
glazing, or cracking. Fuel Injection System Inspection: Have injection
pressure and spray pattern checked by a specialist every 1,500 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).
Glow Plugs: 15-20 Nm (11-15 lb-ft).
Oil Pan Drain Plug: 59-69 Nm (44-51 lb-ft).
Oil Filter Cartridge: Hand-tighten plus 3/4 turn after the sealing
gasket contacts the base.
The Mitsubishi S4S engine is found in a wide array of machinery where
low-end torque, durability, and service simplicity are paramount. Common
applications include: Forklift Trucks: Mitsubishi, Caterpillar, and
Komatsu forklifts in the 5 to 8 ton capacity range. Agricultural
Tractors: Used in various Japanese and Korean compact and medium-duty
agricultural tractors (e.g., Mitsubishi MT series, Iseki).
Construction Equipment: Powers smaller hydraulic excavators (e.g., early
model Komatsu PC series), vibratory rollers, and mobile air compressors.
Generator Sets: Serves as a prime mover for industrial generator sets in
the 30-50 kVA power range, operating at constant 1,500 or 1,800 rpm.
Pumping Equipment: Drives large-volume irrigation pumps, firefighting
pumps, and industrial dewatering systems. Marine Auxiliary: Used in some
marine applications as a propulsion engine for small workboats or as a
generator drive.
____________________________________________________________________________________
| Industrial Engines Technical Specifications |
| Car Engines Technical Specifications |
| Small Engines Technical Specifications |
| Outboard Engines Technical Specifications |
