Mitsubishi S4E Specifications
| Engine Model: Mitsubishi S4E |
| Engine Type: 4-cycle inline 4-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 159.3 cu.in (2.61 L) |
| Rated Engine Power: 49.3 Hp (36.8 kW) at 2400 rpm |
| Fuel System Type: Direct fuel injection |
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The Mitsubishi S4E is a classic, square-design
four-cylinder diesel engine, engineered for heavy-duty industrial and
material handling applications. This 2.610-liter power plant features an
equal bore and stroke of 94 mm, contributing to a balanced mechanical
design with a favorable torque characteristic across the speed range. As
a direct injection engine, it prioritizes fuel efficiency and
thermodynamic efficiency, delivering reliable power for continuous-duty
cycles.
Its design and construction embody an era of industrial engine
development where mechanical robustness, serviceability, and long
operational life were paramount. The engine is characterized by a
straightforward, gear-driven valve train and a mechanical fuel system,
making it highly serviceable with standard tools. It served as a
foundational power source for a generation of forklifts, small
construction equipment, and industrial power units, valued for its
durability and predictable performance.
Manufacturer: Mitsubishi Heavy Industries, Ltd.
Engine Model: S4E.
Engine Type: 4-cycle, water-cooled, vertical inline, direct injection
diesel.
Aspiration: Naturally aspirated.
Emission Compliance: Manufactured before widespread modern emission
regulations; conforms to historical industrial standards.
Management System: Mechanical fuel injection with mechanical governor.
Number of Cylinders: 4.
Bore: 94 mm (3.701 in).
Stroke: 94 mm (3.701 in).
Displacement: 2.610 L (2610 cc) (159.3 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: 36.8 kW (49.3 hp) at 2,400 rpm.
Maximum Gross Torque: 137 Nm (101 lb-ft) at 1,600 rpm.
Rated Speed: 2,400 rpm.
Idle Speed: 650-750 rpm.
The cylinder block is a sturdy, heavily webbed casting manufactured from
high-strength gray iron. Its design provides a solid foundation, with
ample material around the cylinder bores and main bearing saddles to
withstand internal forces. The cylinder bores are machined and honed
directly into the block material. The crankshaft is a forged steel
component, supported by five main bearings.
This five-main-bearing configuration provides critical support for the
crankshaft, ensuring stable rotation and minimizing deflection under
load. 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 manufactured from
aluminum alloy and incorporate a specific combustion bowl design
optimized for the direct injection swirl chamber. The piston ring pack
consists of two compression rings and one oil control ring.
A single-piece cast iron cylinder head is employed, secured to the block
with high-tensile studs and nuts. The head accommodates one intake and
one exhaust valve per cylinder. Valve seat inserts are manufactured from
hardened material for wear resistance. The valve train operates on an
overhead valve (OHV) design, with the camshaft located in the cylinder
block. The camshaft is gear-driven from the crankshaft, providing
positive and reliable timing without belts or chains.
The camshaft actuates the valves via solid pushrods and rocker arms.
Rocker arms are mounted on a stationary shaft attached to the cylinder
head. Valve clearance is set and maintained by a screw and locknut
adjustment on each rocker arm. The specified cold valve clearance is
0.25 mm (0.010 in) for both intake and exhaust valves. The cylinder head
houses the direct injection fuel injectors, which are positioned at an
angle to direct fuel into the piston bowl.
The engine utilizes a mechanical, inline pump-line-nozzle fuel injection
system. Core components are a mechanical fuel lift pump, an inline
injection pump with four individual pumping elements, high-pressure
steel 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 high pressure directly into the main combustion chamber.
A mechanical centrifugal governor, integral to the injection pump,
regulates engine speed by controlling the fuel rack position. The static
injection timing is set at 24 degrees before top dead center (TDC). The
specified injection pressure range is 120 to 130 kg/cm2 (1,707 to 1,849
psi / 11.8 to 12.7 MPa). Fuel filtration is provided by a primary
sediment bowl and a secondary inline paper filter element.
Lubrication is provided by a forced-feed, full-flow wet sump system. A
gear-type oil pump, driven from the crankshaft, draws oil from the sump
through a pickup tube and screen. Pressurized oil is directed through a
full-flow, replaceable cartridge or canister-type oil filter. Filtered
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 reliable lubrication with a simple network of
internal oil passages. The specified engine oil is API CC or CD grade.
Total oil capacity is 7.0 liters (7.4 US qt), including the filter. The
oil pan is a stamped steel 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 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 cooling system requires a mixture of water and ethylene-glycol
antifreeze. The specified minimum compression pressure is 27 kg/cm2 (384
psi) at a cranking speed of 150-200 rpm, which is a key indicator of
cylinder sealing and combustion chamber health.
Intake System: Consists of an oil bath or dry-type air cleaner and a
cast iron intake manifold. Exhaust System: Comprises a cast iron exhaust
manifold and a downpipe.
Electrical System: Operates on a 12V or 24V system, with 24V being
common for industrial applications. A corresponding starter motor and DC
generator or alternator are fitted. Cold starting may be assisted by an
intake manifold heater or, on some variants, glow plugs. An electric
stop solenoid or manual pull cable acts on the injection pump rack.
Governor: A mechanical centrifugal governor is integrated within the
fuel injection pump.
Length (Front Face of Block to Flywheel Housing): 685 mm (26.97 in).
Width (Overall): 550 mm (21.65 in).
Height (Overall, from sump to valve cover): 720 mm (28.35 in).
Dry Weight (with standard accessories): 220 kg (485 lb).
Engine Oil Change: Every 250 operating hours. Oil Filter Replacement:
Every oil change (250 hours). Fuel Filter Replacement: Service sediment
bowl daily; replace secondary filter element every 500 hours. Air
Cleaner Element Service: Clean oil bath or replace dry element every
100-250 hours, depending on environment.
Valve Clearance Adjustment: Check and adjust every 500 operating hours.
Coolant Replacement: Drain, flush, and refill every 1,000 operating
hours or annually. Fan Belt Tension Check/Adjustment: Inspect and adjust
tension every 250 hours. Fuel Injection System Inspection: Check
injection pressure and spray pattern every 1,500 hours.
Cylinder Head Bolts: Tighten in the specified sequence to a final torque
of 118 Nm (87 lb-ft) [12.0 kgm].
Main Bearing Cap Bolts: 103 Nm (76 lb-ft) [10.5 kgm].
Connecting Rod Cap Bolts: 83 Nm (61 lb-ft) [8.5 kgm].
Flywheel to Crankshaft Bolts: 118 Nm (87 lb-ft).
Fuel Injector Holder: 59-69 Nm (44-51 lb-ft).
Oil Pan Drain Plug: 49-59 Nm (36-44 lb-ft).
Oil Filter Canister: Tighten the center bolt to 25-30 Nm (18-22 lb-ft).
The Mitsubishi S4E engine was extensively used in heavy-duty industrial
vehicles, particularly in the material handling sector, throughout the
1970s and 1980s. Common applications include: Forklift Trucks:
Mitsubishi FG, FD, and FDR series forklifts; Clark C500 and Yale GP
series; TCM and Daewoo heavy-duty forklifts. Construction Equipment:
Small hydraulic excavators (e.g., early Mitsubishi, UH-04 series),
vibratory rollers, and mobile light towers.
Industrial Power Units: Stationary pumps, agricultural machinery
(irrigation pumps, threshers), and generator sets in the 20-30 kVA
range. Ground Support Equipment: Aircraft tow tractors and belt loaders.
Small Trucks and Buses: Found in some light-duty commercial trucks and
mini-buses in Asian markets.
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