Mitsubishi S4Q2 Specifications
| Engine Model: Mitsubishi S4Q2 |
| Engine Type: 4-cycle inline 4-cylinder OHV forced-feed lubrication liquid-cooled diesel |
| Total Displacement: 152.9 cu.in (2.51 L) |
| Rated Engine Power: 46.4-48.5 Hp (34.6-36.2 kW) at 2400 rpm |
| Fuel System Type: Indirect fuel injection |
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The Mitsubishi S4Q2 is a durable four-cylinder
diesel engine engineered for reliable and consistent performance in
industrial and construction applications. This 2.505-liter power unit is
produced in both naturally aspirated and turbocharged configurations,
providing a flexible power solution for equipment with varying load
demands. As an Indirect Injection (IDI) engine featuring a swirl
pre-combustion chamber, it offers controlled combustion, reduced
mechanical noise, and dependable cold-start capability.
The engine's design emphasizes structural integrity and long-term
serviceability, with components laid out for straightforward maintenance
access. Its robust construction is suited to the cyclical loads and
challenging environments of construction sites. Beyond mobile machinery,
the S4Q2 is also engineered for constant-speed duty, making it a common
and trusted prime mover for industrial generator sets, where stable
frequency and voltage output are critical requirements.
Manufacturer: Mitsubishi Heavy Industries Engine and Turbocharger, Ltd.
(MHIET).
Engine Model: S4Q2 (Naturally Aspirated), S4Q2-T (Turbocharged).
Engine Type: 4-cycle, water-cooled, vertical inline, indirect injection
diesel.
Aspiration: Naturally aspirated or Turbocharged (T model).
Emission Compliance: Manufactured in variants conforming to various
regional standards, including EPA Tier 2 and Tier 3 equivalents for
industrial engines.
Management System: Mechanical fuel injection with mechanical governor.
Number of Cylinders: 4.
Bore: 88 mm (3.465 in).
Stroke: 103 mm (4.055 in).
Displacement: 2.505 L (2505 cc) (152.9 cu in).
Compression Ratio: 22:1.
Firing Order: 1-3-4-2.
Rotation Direction: Counter-clockwise when viewed from the flywheel
side.
Maximum Net Power Output (Naturally Aspirated): 34.6 kW (46.4 hp) at
2,500 rpm.
Maximum Net Power Output (Turbocharged S4Q2-T): 36.2 kW (48.5 hp) at
2,400 rpm.
Maximum Net Torque (Turbocharged): 155 Nm (114 lb-ft) at 1,600 rpm.
Rated Speed (Industrial): 2,400-2,500 rpm. Constant Speed (Generator):
1,500 rpm (50 Hz) or 1,800 rpm (60 Hz). Idle Speed: 750-850 rpm.
The cylinder block is a high-rigidity, single-piece casting manufactured
from high-grade gray iron. It incorporates a closed-deck design, where
the top surface of the block forms a solid, unbroken deck around the
cylinder bores. This architecture provides superior resistance to
cylinder head gasket loads and contains combustion pressure effectively,
minimizing bore distortion.
The cylinder bores are precision-machined and honed directly into the
block material, a linerless design that ensures efficient heat transfer
from the cylinder walls to the surrounding coolant passages. The
crankshaft is a forged steel component, supported by five main bearings.
This five-bearing support system ensures exceptional crankshaft
stability, dampens vibrations, and contributes directly to the engine's
smooth running characteristics and potential for long service life.
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 IDI swirl chamber system. 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 is designed to accommodate
one intake and one exhaust valve per cylinder. Valve seat inserts are
manufactured from hardened, heat-resistant alloy material to ensure
durability under continuous high-temperature operation. 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, a
manual procedure required at scheduled maintenance intervals. 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 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. It supplies fuel at
high pressure to pintle-type nozzles that discharge into the
pre-combustion swirl chamber.
A mechanical centrifugal governor, integral to the injection pump,
regulates engine speed by controlling the position of the fuel rack. For
generator set applications, an isochronous governor or a more precise
electronic actuator may be fitted to maintain a constant speed under
varying electrical load. Fuel filtration is a two-stage process,
involving a primary sedimentor/water separator and a secondary fine
filter to protect the precision components of the injection system.
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.
In the turbocharged (T) variant, an additional oil feed and drain line
services the turbocharger center bearing. The specified engine oil is
API CF-4 grade or higher. Total oil capacity, including the filter, is
6.5 liters (6.9 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. A 50/50 mixture is standard for full corrosion
protection and freeze resistance down to -37°C (-35°F). Total cooling
system capacity is 5.5 liters (5.8 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 on the turbocharged
(S4Q2-T) model, a turbocharger and associated intake piping. The
naturally aspirated version uses a simple intake manifold.
Exhaust System: Comprises an exhaust manifold. On the turbocharged
model, the manifold feeds exhaust gas to the turbocharger turbine,
exiting via a downpipe to the machine's or generator set's exhaust
silencer.
Electrical System: Operates on a 12V or 24V system, with 24V being
common for industrial and generator applications. A corresponding
starter motor and alternator are fitted. The engine incorporates a glow
plug system for each cylinder, controlled by a key-switch or timer
module for cold starting. An electric stop solenoid acts on the
injection pump rack.
Length (Front Face of Block to Flywheel Housing): 740 mm (29.13 in).
Width (Overall): 540 mm (21.26 in).
Height (Overall, from sump to valve cover): 715 mm (28.15 in).
Dry Weight (with standard accessories): 195 kg (430 lb).
Engine Oil Change: Every 250 operating hours. Oil Filter Replacement:
Every oil change (250 hours). Fuel Filter Replacement: Replace primary
and secondary filter elements every 500 operating hours. Air Cleaner
Element Service: Clean or replace based on restriction indicator;
inspect regularly, especially in dusty 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. Fuel Injection System Inspection: Have injection
pressure and spray pattern checked by a specialist every 1,500 hours.
Cylinder Head Nuts: Tighten in the specified multi-step crisscross
sequence to a final torque of 108-118 Nm (80-87 lb-ft). Main Bearing Cap
Bolts: 88-98 Nm (65-72 lb-ft).
Connecting Rod Cap Bolts: 59-69 Nm (44-51 lb-ft).
Flywheel to Crankshaft Bolts: 108-118 Nm (80-87 lb-ft).
Fuel Injector Holder: 59-69 Nm (44-51 lb-ft).
Glow Plugs: 15-20 Nm (11-15 lb-ft).
Oil Pan Drain Plug: 49-59 Nm (36-44 lb-ft).
Oil Filter Cartridge: Hand-tighten plus 3/4 turn after the sealing
gasket contacts the base.
The Mitsubishi S4Q2 engine is deployed in a range of industrial and
construction equipment where its dependable power and constant-speed
capability are valued. Common applications include: Construction
Machinery: Used in various mid-sized vibratory rollers, asphalt pavers,
and compact drilling rigs. Material Handling: Selected models of
medium-capacity forklifts (3.5 to 5 ton) and stationary hydraulic power
units.
Generator Sets: A prevalent engine for industrial generator sets in the
25-40 kVA power range, both as open and silent canopied units, operating
at 1,500 or 1,800 rpm. Agricultural Equipment: Powers larger irrigation
pumps, feed processing equipment, and certain stationary farm machinery.
Air Compressors: Serves as the diesel driver for larger portable and
stationary screw-type air compressors. Pumping Equipment: Used in
high-volume water transfer, firefighting, and dewatering pump units.
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