Mitsubishi S3L Specifications
| Engine Model: Mitsubishi S3L |
| Engine Type: 4-cycle inline 3-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 68.6 cu.in (1.13 L) |
| Rated Engine Power: 20 Hp (14.9 kW) at 2400 rpm |
| Fuel System Type: Indirect fuel injection |
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The Mitsubishi S3L is a compact, three-cylinder
diesel engine engineered for light-duty industrial, agricultural, and
auxiliary power applications where a balance of modest power,
operational smoothness, and fuel efficiency is required. This
1.13-liter, naturally aspirated power plant employs an indirect
injection combustion system with a swirl pre-combustion chamber,
delivering controlled combustion, reduced mechanical noise, and reliable
cold-start performance. The three-cylinder configuration offers a
notable improvement in balance and smoothness over comparable
two-cylinder engines, reducing inherent vibration.
Its design emphasizes simplicity, durability, and ease of maintenance,
with a cast iron block and a gear-driven valve train forming a robust
mechanical foundation. The S3L is constructed for long service life in
moderate-duty cycles, serving as a dependable prime mover for small
generator sets, agricultural machinery, compact construction equipment,
and hydraulic power units where its compact dimensions and
three-cylinder refinement are distinct advantages.
Manufacturer: Mitsubishi Heavy Industries, Ltd.
Engine Model: S3L.
Engine Type: 4-cycle, water-cooled, vertical inline, indirect 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 centrifugal
governor.
Number of Cylinders: 3.
Bore: 78 mm (3.071 in).
Stroke: 78.5 mm (3.091 in).
Displacement: 1.125 L (1125 cc) (68.6 cu in).
Compression Ratio: 22.0:1.
Firing Order: 1-3-2.
Rotation Direction: Counter-clockwise when viewed from the flywheel
side.
Maximum Gross Power Output: 14.9 kW (20.0 hp) at 2,400 rpm
(representative value; output varies by governed speed and application).
Maximum Gross Torque: 54 Nm (39.8 lb-ft) at 1,800 rpm.
Rated Speed: 2,200-2,400 rpm for variable-speed applications; 1,500 or
1,800 rpm for constant-speed generator sets. Idle Speed: 750-850 rpm.
The cylinder block is a sturdy, compact casting manufactured from
high-strength gray iron. Its design provides a solid structural
foundation for the three cylinders, with adequate webbing between the
bores and around the main bearing saddles. 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 four main
bearings.
This four-main-bearing configuration is standard and necessary for a
three-cylinder crankshaft, providing essential support to manage dynamic
forces and ensure stable rotation, which is key to the engine's smooth
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 fundamental maintenance task. 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
three-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.
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. The
specified engine oil is API CC or CD grade. Total engine oil capacity is
3.7 liters (3.9 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 3.0 liters (3.2 US qt) for the engine side, excluding the
radiator and external hose volume.
| Intake and Exhaust Systems |
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. An electric stop solenoid or manual pull cable acts
on the injection pump rack.
Length (Front Face of Block to Flywheel Housing): 536 mm (21.10 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): 135 kg (297.6 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. 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, center bolt to 20-25 Nm (15-18 lb-ft).
The Mitsubishi S3L engine was widely used in compact industrial and
agricultural machinery where its three-cylinder smoothness and modest
power output were well-suited. Common applications include: Agricultural
Tractors: Compact agricultural and garden tractors. Construction
Equipment: Very small vibratory rollers, light towers, and
micro-excavators. Generator Sets: Mobile and stationary generator sets
in the 10-15 kVA power range.
Pumping Equipment: Small to medium irrigation pumps and industrial
transfer pumps. Material Handling: Light-duty forklifts and hydraulic
power packs. Agricultural Machinery: Rice transplanters, power tillers,
and small threshing machines. Marine Applications: Auxiliary power for
small boats and as a propulsion engine for tiny dinghies and workboats.
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