Mitsubishi S4L Specifications
| Engine Model: Mitsubishi S4L |
| Engine Type: 4-cycle inline 4-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 91.5 cu.in (1.5 L) |
| Rated Engine Power: 26.7 Hp (19.9 kW) at 2400 rpm |
| Fuel System Type: Indirect fuel injection |
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The Mitsubishi S4L is a compact, four-cylinder
diesel engine engineered for light to medium-duty industrial,
agricultural, and auxiliary power applications where smooth operation,
reliability, and fuel efficiency are primary considerations. This
1.50-liter, naturally aspirated power plant employs an indirect
injection combustion system with a swirl pre-combustion chamber,
delivering controlled combustion characteristics, reduced mechanical
noise, and dependable cold-start performance.
The four-cylinder configuration provides inherent primary and secondary
mechanical balance, resulting in very low levels of vibration, a
significant advantage for operator comfort in mobile machinery and
stable operation in generator sets. Its design emphasizes mechanical
simplicity, durability, and straightforward maintenance, featuring a
robust cast iron block and a gear-driven valve train. The S4L serves as
a dependable and smooth-running prime mover for equipment such as small
generator sets, compact construction machinery, agricultural implements,
and material handling equipment, where its four-cylinder refinement and
proven indirect injection technology are valued assets.
Manufacturer: Mitsubishi Heavy Industries, Ltd.
Engine Model: S4L.
Engine Type: 4-cycle, water-cooled, vertical inline, indirect injection
diesel.
Aspiration: Naturally aspirated.
Emission Compliance: Manufactured before the implementation of
contemporary emission regulations; conforms to historical industrial
engine standards.
Management System: Mechanical fuel injection with mechanical centrifugal
governor.
Number of Cylinders: 4.
Bore: 78 mm (3.071 in).
Stroke: 78.5 mm (3.091 in).
Displacement: 1.50 L (1500 cc) (91.5 cu in).
Compression Ratio: 22.0:1.
Firing Order: 1-3-4-2.
Rotation Direction: Counter-clockwise when viewed from the flywheel
side.
Maximum Gross Power Output: 19.9 kW (26.7 hp) at 2,400 rpm
(representative value; governed output varies by application).
Maximum Gross Torque: 72 Nm (53.1 lb-ft) at 1,800 rpm.
Rated Speed: 2,200-2,400 rpm for variable-speed industrial use; 1,500 or
1,800 rpm for constant-speed generator applications.
Idle Speed: 750-850 rpm.
The cylinder block is a sturdy, compact casting manufactured from
high-strength gray iron. Its design provides a rigid structural
foundation for the four cylinders, with adequate webbing between the
bores and substantial material around the 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 or
high-grade cast iron component, supported by five main bearings.
This five-main-bearing configuration is essential for a four-cylinder
inline engine, providing critical support to ensure stable crankshaft
rotation, minimize deflection, and contribute directly to the engine's
smooth and vibration-free operation. 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 compression rings and one oil control ring.
A single-piece cast iron cylinder head is employed, secured to the block
with 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 and longevity. 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 a positive and maintenance-free timing drive.
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, a scheduled 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 utilizes a mechanical, inline pump-line-nozzle fuel injection
system. Core components include a mechanical fuel lift pump, a
four-element inline injection pump, high-pressure fuel lines, and
throttle-type (pintle) injectors. The injection pump is a jerk-pump
design, driven by the engine's gear train. It supplies fuel at high
pressure to nozzles that discharge into the pre-combustion swirl
chamber.
A centrifugal fly-weight type mechanical governor, integral to the
injection pump, regulates engine speed by controlling the position of
the fuel rack. Fuel filtration is provided by a separate-type
paper-element cartridge fuel filter equipped with a water drain cock.
This filter assembly is critical for protecting the precision components
of the injection system from contamination and water ingress, requiring
regular inspection and service.
Lubrication is provided by a forced-feed, full-flow wet sump system. A
trochoid (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 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 reliable pressure-feed lubrication to all
critical components. The specified engine oil is API CC or CD grade.
Total engine oil capacity is 5.4 liters (5.7 US qt). 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 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 cooling system requires
a mixture of water and ethylene-glycol antifreeze. Total cooling system
capacity is 4.0 liters (4.2 US qt) for the engine side, excluding the
radiator and external hose volume.
Intake System: Consists of an air cleaner and a cast iron or aluminum
intake manifold. Exhaust System: Comprises a cast iron exhaust manifold
and a downpipe.
Electrical System: Operates on a 12V system. A 12V electric starter
motor and a 12V alternator or DC generator are fitted. The engine
incorporates a glow plug system for cold starting, controlled by a
key-switch or timer module. An electric stop solenoid or manual pull
cable acts on the injection pump rack.
Governor: A mechanical centrifugal fly-weight type governor is standard,
integrated within the fuel injection pump.
Length (Front Face of Block to Flywheel Housing): 620 mm (24.40 in).
Width (Overall): 433 mm (17.04 in).
Height (Overall, from sump to valve cover): 572 mm (22.52 in).
Dry Weight (with standard accessories): 155 kg (341.7 lb).
Engine Oil Change: Every 250 operating hours. Oil Filter Replacement:
Every oil change (250 hours). Fuel Filter Replacement: Replace the
paper-element cartridge every 500 hours; drain water from the filter
bowl daily or weekly. Air Cleaner Element Service: Clean or replace
based on environment; inspect every 100 hours in dusty conditions. 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; replace at 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 Bolts: Tighten in the specified sequence to a final torque
of 78-88 Nm (58-65 lb-ft).
Main Bearing Cap Bolts: 69-78 Nm (51-58 lb-ft).
Connecting Rod Cap Bolts: 49-59 Nm (36-44 lb-ft).
Flywheel to Crankshaft Bolts: 78-88 Nm (58-65 lb-ft).
Fuel Injector Holder: 49-59 Nm (36-44 lb-ft).
Glow Plugs: 15-20 Nm (11-15 lb-ft).
Oil Pan Drain Plug: 29-39 Nm (21-29 lb-ft).
Oil Filter Cartridge/Canister: Hand-tighten plus 3/4 turn after gasket
contact; for a canister, tighten the center bolt to 20-25 Nm (15-18
lb-ft).
The Mitsubishi S4L engine was applied in a variety of compact industrial
and agricultural equipment where its smooth four-cylinder operation and
reliable indirect injection performance were advantageous. Common
applications include: Agricultural Tractors: Compact and utility
agricultural tractors. Construction Equipment: Small vibratory rollers,
light towers, concrete mixers, and micro-excavators.
Generator Sets: Mobile and stationary generator sets in the 15-20 kVA
power range. Pumping Equipment: Medium-capacity irrigation pumps,
firefighting pumps, and industrial transfer pumps. Material Handling:
Light to medium-duty forklifts and hydraulic power units. Agricultural
Machinery: Powers implements such as rotary tillers, feed grinders, and
small threshers. Marine Applications: Used as an auxiliary generator
drive or propulsion engine for small fishing boats and workboats.
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