Mitsubishi S4L2 Specifications
| Engine Model: Mitsubishi S4L2 |
| Engine Type: 4-cycle inline 4-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 107.3 cu.in (1.76 L) |
| Rated Engine Power: 38.6 Hp (28.8 kW) at 3000 rpm |
| Fuel System Type: Direct or indirect fuel injection |
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The Mitsubishi S4L2 is a compact, four-cylinder
diesel engine engineered for reliable and efficient power delivery in a
diverse range of light industrial and construction applications. This
1.758-liter power unit is designed to provide a favorable balance of
specific output, mechanical durability, and operational smoothness
within a constrained physical package. It is available in configurations
featuring either an Indirect Injection (IDI) system with a swirl
pre-combustion chamber or a Direct Injection (DI) system, allowing
selection based on priorities for cold-start performance, noise, and
fuel economy.
The engine's architecture emphasizes robustness and serviceability, with
a design that withstands the variable loads and harsh environments
common in equipment such as compact excavators, forklifts, and generator
sets. Its straightforward mechanical fuel system and accessible
component layout contribute to ease of maintenance and long service
life, establishing it as a dependable power source in global markets.
Manufacturer: Mitsubishi Heavy Industries Engine and Turbocharger, Ltd.
(MHIET).
Engine Model: S4L2.
Engine Type: 4-cycle, water-cooled, vertical inline diesel.
Combustion System: Indirect Injection (Swirl Chamber) or Direct
Injection.
Aspiration: Naturally aspirated.
Management System: Mechanical fuel system with mechanical governor on
base models.
Later emission-compliant variants employ electronic control systems.
Number of Cylinders: 4.
Bore: 78 mm (3.071 in).
Stroke: 92 mm (3.622 in).
Displacement: 1.758 L (1758 cc) (107.3 cu in).
Compression Ratio: Indirect Injection: 22:1. Direct Injection: 18:1.
Firing Order: 1-3-4-2.
Rotation Direction: Counter-clockwise when viewed from the flywheel
side.
Maximum Gross Power Output: 28.8 kW (38.6 hp) at 3,000 rpm for common
industrial variants.
Maximum Gross Torque: 97 Nm (71.5 lb-ft) at 1,800-2,000 rpm.
Maximum Governed Speed: 3,000 rpm for variable-speed applications; 1,500
or 1,800 rpm for constant-speed generator sets.
Idle Speed: 800-1,000 rpm (adjustable).
Emission Compliance: Manufactured in variants conforming to various
regional standards, including earlier directives and more recent Tier 4f
/ Stage V regulations through application-specific configurations with
advanced after-treatment.
The cylinder block is a high-rigidity, single-piece casting manufactured
from gray iron. It employs a closed-deck design, where the upper section
of the cylinder bores is integrated into a solid deck, providing
superior strength to contain combustion pressures and minimize cylinder
bore distortion. The cylinder bores are precision-honed directly into
the block material, a linerless construction that promotes effective
heat transfer to the surrounding coolant jackets.
The crankshaft is a forged steel or high-strength nodular cast iron
component, supported by five main bearings. This five-bearing design
ensures exceptional crankshaft stability, reduces flexural vibration,
and contributes to the engine's smooth operational character. 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. IDI variant pistons feature a flat or shallow dish
crown, while DI variant pistons incorporate a specific re-entrant
combustion bowl engineered to generate controlled air swirl for optimal
mixing. 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, 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, heat-resistant alloy material to ensure durability under
continuous thermal cycling. 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 and 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, requiring periodic manual inspection and adjustment
as part of routine maintenance. The cylinder head design is distinct
between IDI and DI types: IDI heads house a pre-combustion swirl chamber
equipped with a glow plug, while DI heads position the injector nozzle
centrally to spray fuel directly into the piston bowl.
The base engine configuration 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. For Indirect Injection engines, the pump supplies
fuel to pintle-type nozzles that discharge into the pre-combustion
chamber.
Direct Injection engines utilize the same pump principle but generate
higher pressure to supply multi-hole pintle nozzles for direct
combustion chamber injection. A mechanical centrifugal governor,
integral to the injection pump, regulates engine speed by controlling
the position of the fuel rack. This system is known for its simplicity
and reliability. Emission-compliant modern variants may utilize an
electronically controlled version of this system or a common rail system
managed by an Engine Control Unit (ECU).
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 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 effective lubrication with a reliable and
simple oil passage network. The specified engine oil is API CD, CF, or
for modern variants, low-ash oils meeting API CJ-4 specifications to
protect exhaust after-treatment devices where fitted. Total oil
capacity, including the filter, is 6.0 liters (6.3 US qt). The oil pan
is a stamped steel or cast aluminum 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 cooling system requires a mixture of ethylene-glycol antifreeze and
clean, deionized water, in a ratio appropriate for the expected minimum
ambient temperature, generally between 30/70 and 50/50. Total cooling
system capacity for the engine side is 3.5 liters (3.7 US qt), excluding
the radiator, hoses, and any external heat exchanger volume.
| Intake and Exhaust Systems |
Intake System: Consists of an air cleaner, intake manifold, and, on DI
models, intake ports engineered to generate controlled swirl for
improved air-fuel mixing. Exhaust System: Comprises an exhaust manifold
and downpipe. On emission-compliant models (e.g., Tier 4f / Stage V),
this system integrates a Diesel Oxidation Catalyst (DOC) and a Diesel
Particulate Filter (DPF), managed by an ECU which controls active
regeneration cycles.
Electrical System: Operates on a 12V system with a 50A alternator. A 12V
starter motor is standard. Indirect Injection models incorporate a glow
plug system for cold starting, typically controlled by a key-switch
position or timer. An electric stop solenoid acts on the injection pump
rack. Advanced emission-compliant versions feature a comprehensive
sensor suite and a dedicated ECU.
Length (Front Face of Block to Flywheel Housing): 678 mm (26.69 in).
Width (Overall): 442 mm (17.40 in).
Height (Overall, from sump to valve cover): 572 mm (22.52 in).
Dry Weight (with standard accessories): 155 kg (342 lb).
Engine Oil Change: Every 250 operating hours for standard models. For
emission-compliant models using low-ash oil, intervals may extend to 500
hours (strictly follow OEM specification). Oil Filter Replacement: Every
oil change. Fuel Filter Replacement: Every 500 operating hours. A water
separator, if equipped, should be drained daily or weekly. Air Cleaner
Element Service: Clean or replace based on restriction indicator;
inspect frequently in dusty operating 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. After-Treatment Service (Tier 4f / Stage V
models): DPF ash cleaning is required at extended intervals (e.g., 4,500
hours), contingent on actual fuel and oil consumption.
Cylinder Head Nuts: Tighten in the specified multi-step crisscross
sequence to a final torque of 88-98 Nm (65-72 lb-ft). Main Bearing Cap
Bolts: 88-98 Nm (65-72 lb-ft).
Connecting Rod Cap Bolts: 49-59 Nm (36-44 lb-ft).
Flywheel to Crankshaft Bolts: 88-98 Nm (65-72 lb-ft).
Fuel Injector Holder: 59-69 Nm (44-51 lb-ft) for DI types.
Glow Plug: 15-20 Nm (11-15 lb-ft) for IDI types.
Oil Pan Drain Plug: 39-49 Nm (29-36 lb-ft).
Oil Filter Cartridge: Hand-tighten plus 3/4 turn after the sealing
gasket contacts the base.
The Mitsubishi S4L2 engine is a widely adopted power source in compact
machinery across multiple industries, valued for its smooth operation
and reliability. Its primary applications include: Compact Excavators:
Caterpillar (CAT) 302.5, 302.7; Yanmar VIO35, VIO45; Bobcat 335, 337;
Takeuchi TB1140, TB125. Compact Wheel Loaders: Schaffer and other
European compact loader brands.
Forklift Trucks: Mitsubishi, CAT, and Komatsu forklifts in the 2.0 to
3.5 ton capacity range. Generator Sets: Mobile and stationary diesel
generators in the 20-30 kVA power range. Agricultural Machinery: Small
agricultural tractors, specialized harvesters, and power units.
Compaction Equipment: Small double-drum rollers and vibratory plate
compactors. Pumping Equipment: Medium-capacity water transfer,
irrigation, and dewatering pumps. Air Compressors: Portable and
stationary diesel-driven air compressors.
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