Mitsubishi S4F Specifications
| Engine Model: Mitsubishi S4F |
| Engine Type: 4-cycle inline 4-cylinder liquid-cooled diesel |
| Total Displacement: 211 cu.in (3.45 L) |
| Rated Engine Power: 90-125 Hp (67-93 kW) at 2300 rpm |
| Fuel System Type: Direct injection |
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The Mitsubishi S4F is a robust, inline
four-cylinder, four-stroke liquid-cooled diesel engine designed for high
reliability across industrial, agricultural, marine, and construction
applications. The S4F is part of Mitsubishi's renowned S-series engine
family, which is widely used in excavators, forklifts, tractors, and
generator sets. Known for its strong low-end torque and balanced power
delivery, the S4F is engineered to perform consistently under demanding
conditions.
The engine is available in both naturally aspirated and turbocharged
configurations (S4F-T), with later variants meeting Tier 3 and Tier 4
emission standards. Its mechanical fuel system and reinforced components
make it a preferred choice for mobile and stationary equipment requiring
long service intervals and durability in harsh environments.
The Mitsubishi S4F engine exemplifies Mitsubishi’s engineering approach
for medium-duty power units, prioritizing torque output, structural
integrity, and ease of maintenance. The engine’s inline four-cylinder
configuration provides inherent balance and smooth operation compared to
three-cylinder designs, while the long-stroke bore/stroke ratio supports
the high torque generation essential for construction and agricultural
machinery.
The direct injection combustion system, combined with a gear-type fuel
injection pump, ensures efficient fuel atomization and reliable
starting. The engine block is constructed from high-grade cast iron,
contributing to vibration damping and resistance to thermal distortion,
while the cylinder head is manufactured from lightweight aluminum alloy
for superior heat dissipation.
A defining feature of the S4F is its replaceable cast-iron cylinder
liners, which are inserted into the block to provide a durable,
wear-resistant surface for piston movement and allow for in-frame
overhauls without complete engine removal. The engine’s reputation
within the industrial sector is defined by its low-end torque peak
occurring as low as 1,500 rpm, its fuel efficiency, and the availability
of service parts across multiple global markets.
Production Period: 1990s - 2010s (approximate)
Engine Code: Mitsubishi S4F (S4F1, S4F2, S4F3 variants)
Configuration: Inline four-cylinder (I4)
Displacement: 3.456 L (211.0 cu.in)
Bore: 100.0 mm (3.94 in)
Stroke: 110.0 mm (4.33 in)
Combustion System: Direct injection
Aspiration: Naturally aspirated (std); turbocharged (S4F-T variant)
Valvetrain: Overhead valve (OHV), 8 valves (2 per cylinder)
Maximum Engine Speed: 2,600-2,800 rpm (application-dependent)
Maximum Power: 90-95 hp (67-70 kW) @ 2,300 rpm
Peak Torque: 210 Nm (155 lb-ft) @ 1,600 - 1,800 rpm
Optional Variant Power (Turbo): 105-125 hp (78-93 kW)
The Mitsubishi S4F cylinder block is manufactured from high-grade cast
iron, providing excellent tensile strength and thermal mass for
sustained medium-duty operation. The cast iron construction also
contributes to effective vibration damping, reducing mechanical noise
and stress on ancillary components. The block features a deep-skirt
design extending below the crankshaft centerline, which enhances
rigidity and resists bore distortion under high combustion pressures
generated by the direct injection system.
A defining feature of the S4F block is the use of replaceable wet-type
cylinder liners. These liners are inserted into the block to provide a
durable, wear-resistant surface for the piston rings while allowing the
coolant to circulate directly around the liner exterior for efficient
heat transfer. Unlike integral bores, this wet-sleeve design facilitates
major overhauls and liner replacement without removing the engine from
the chassis.
Five main bearings support the drop-forged steel crankshaft. The
crankshaft and camshaft are forged from high-strength iron alloys,
incorporating chromium and molybdenum for enhanced toughness and fatigue
resistance, which is critical for the high compression ratios of diesel
operation.
The cylinder head is manufactured from cast aluminum alloy, selected for
its superior thermal conductivity and lightweight properties. The
aluminum construction allows for rapid heat dissipation from the
combustion chambers, preventing hotspots and reducing the likelihood of
pre-ignition or gasket failure. The head incorporates overhead valves
actuated via mechanical pushrods from a block-mounted camshaft.
The engine features two valves per cylinder (one intake, one exhaust)
for a total of eight valves. The valves have a stem diameter of 8.0 mm.
The combustion chamber design is a direct injection type, with the
injector positioned centrally to promote efficient fuel atomization and
mixing, distinct from indirect injection designs with pre-combustion
chambers present in some other S-series engines like the S4L. The valve
seats are replaceable, and valve lash requires periodic manual
adjustment.
Valve Clearance (Cold):
Intake: 0.20 - 0.25 mm (0.008 - 0.010 in)
Exhaust: 0.20 - 0.25 mm (0.008 - 0.010 in)
The fuel system utilizes a mechanical direct injection system with a
gear-type fuel injection pump (inline or distributor type, depending on
the variant). The injection pump is mounted on the side of the engine
and driven by the gear train from the crankshaft. The high-pressure
injection lines deliver fuel directly to the combustion chambers without
pre-combustion chambers, which is characteristic of the S4F’s direct
injection design.
A mechanical feed pump draws fuel from the tank and delivers it through
a fuel filter equipped with a water separator and a hand-priming lever.
The system is equipped with a mechanical governor integrated into the
injection pump to maintain stable engine speed under varying loads, a
critical feature for generator sets and PTO-driven agricultural
implements.
The lubrication system employs a wet-sump design with a gear-type pump.
The circulating oil passes through a spin-on full-flow oil filter. The
system includes an oil cooler to maintain optimal viscosity under
continuous high-load operation. Total system capacity, including the
filter, is 9.0 to 10.0 liters (9.5 to 10.6 qt).
Recommended Oil: Diesel-rated SAE 15W-40 or SAE 30 (API CI-4 or higher)
Oil Change Interval: 250 hours (industrial / marine) or 5,000 - 7,500
miles (mobile)
The cooling system is pressurized using a water-cooled design with a
crossflow radiator. A centrifugal water pump circulates coolant through
the cylinder block, cylinder head, and heat exchanger. A wax-element
thermostat regulates the coolant flow, with a nominal opening
temperature of 76 - 82°C (169 - 180°F). The system is designed to manage
the thermal load of the engine without a turbocharger in standard
configurations.
Coolant Capacity: 7.5 - 8.5 L (7.9 - 9.0 qt) (engine only)
Coolant Specification: 50/50 ethylene glycol antifreeze and distilled
water
Intake System: The intake system utilizes a heavy-duty dry-type air
cleaner with a replaceable paper element and a dust evacuator valve for
dusty environments common in construction and agricultural settings.
Exhaust System: The exhaust system is constructed from cast iron and may
be fitted with a water-cooled exhaust manifold in marine and generator
applications.
Electrical System: The engine is equipped with a 12V or 24V electrical
system. The system includes a high-torque reduction-gear starter and
glow plugs for cold-start pre-heating. Starter Motor: High-torque
reduction-gear type. Alternator: 12V / 35A or 50A (or 24V equivalent for
industrial specifications).
Overall Length: 650 mm (25.6 in)
Overall Width: 690 mm (27.2 in)
Overall Height: 650 mm (25.6 in)
Dry Weight (complete engine): 200 kg (441 lb)
Engine Oil: SAE 15W-40 or SAE 30, API CI-4 or higher
Oil Capacity (with filter change): 9.5 L (10.0 qt)
Oil Change Interval: 250 Hours (Industrial) / 5,000 miles (Mobile)
Fuel Filter: Replace at 500 hours (spin-on element)
Coolant Capacity: 8.0 L (8.5 qt) (engine only)
Coolant Specification: 50/50 Ethylene Glycol Mix
Valve Clearance (Cold): Intake: 0.25 mm (0.010 in); Exhaust: 0.25 mm
(0.010 in)
Engine Idle Speed: 650 - 750 rpm
Injection Pump Timing: Check nameplate for specific static timing
(10-14° BTDC)
Cylinder Head Bolts, Stage 1: 30 Nm (22 lb-ft)
Cylinder Head Bolts, Stage 2: 60 Nm (44 lb-ft)
Cylinder Head Bolts, Stage 3: 90 Nm (66 lb-ft) + 90° turn
Connecting Rod Cap Bolts: 85 Nm (63 lb-ft)
Main Bearing Cap Bolts: 120 Nm (89 lb-ft)
Flywheel Bolts: 110 Nm (81 lb-ft)
Injector Holders: 70 Nm (52 lb-ft)
Glow Plugs: 15 Nm (11 lb-ft)
Construction Equipment:
Mini excavators (e.g., Kato HD250)
Wheel loaders
Road rollers
Asphalt / concrete mixers
Logistics and Material Handling
Industrial forklifts (Mitsubishi FD20/FD30, TCM)
Mobile pump units
Agricultural Equipment:
Mid-sized tractors
Power tillers
Irrigation pumps
Marine Propulsion:
Small fishing boats
Auxiliary generator sets for yachts
Power Generation:
Standby generator sets
Prime power generators (S4F3-T variant)
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