Mitsubishi 4DQ50 Specifications
| Engine Model: Mitsubishi 4DQ50 |
| Engine Type: 4-cycle inline 4-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 127.2 cu.in (2.08 L) |
| Rated Engine Power: 55 Hp (40 kW) at 2500 rpm |
| Fuel System Type: Indirect injection |
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The Mitsubishi 4DQ50 is a 2.1-liter, naturally
aspirated, inline four-cylinder diesel engine manufactured by Mitsubishi
Heavy Industries. This powerplant belongs to the QD series engine
family, a platform engineered for industrial applications including
forklifts, construction machinery, agricultural equipment, and marine
auxiliary power. The 4DQ50 has earned a reputation for robust low-end
torque, fuel efficiency, and extended service life under continuous load
conditions.
The engine operates on a four-stroke, compression-ignition cycle with a
vertical, water-cooled inline configuration. The swirl combustion
chamber design, often referred to as indirect injection, reduces
combustion noise and nitrogen oxide emissions while improving cold
startability compared to direct injection designs of the same era.
Mitsubishi engineered the 4DQ50 with a Bosch PES-type in-line injection
pump and DN-type injection nozzles, providing precise fuel metering for
the 50 to 52 horsepower output range.
The engine carries a compression ratio of 21:1 and maintains a standard
compression pressure specification above 20 kg/cm2 at a cranking speed
of 150 to 200 rpm. The Mitsubishi 4DQ50 incorporates a forced
lubrication system with a trochoid oil pump, a full-flow oil filter with
a paper element, and a wax-type thermostat for cooling system
regulation. The engine is found in Mitsubishi forklifts, J.I. Case
industrial equipment, small marine vessels such as Dutch steel cruisers
and barges, and various agricultural machines.
The Mitsubishi 4DQ50 is a four-stroke, compression-ignition, inline
four-cylinder diesel engine. The induction system is naturally aspirated
without turbocharging equipment. Total displacement measures 2,084 cc,
equivalent to 127 cubic inches. The bore dimension is 84 mm (3.31 in),
and the stroke dimension is 94 mm (3.70 in). The compression ratio is
fixed at 21:1. The firing order sequence is 1-3-4-2, following the
standard configuration for inline four-cylinder engines. Direction of
revolution, viewed from the timing gear case, is clockwise.
Maximum power output ranges from 37 kW to 40 kW, equivalent to 50 hp to
55 hp, at an engine speed of 2,500 rpm for intermittent industrial
service. Continuous power rating is 30 kW to 34 kW (40 hp to 45 hp) for
generator and marine propulsion applications. The combustion system is a
swirl chamber type, a form of indirect injection where a precombustion
chamber generates intense air swirl to promote air-fuel mixing before
ignition.
The cylinder block is constructed from cast iron, providing rigidity,
vibration damping, and wear resistance required for prolonged service in
industrial and marine environments. The block is an inline four-cylinder
design with full-length water jackets surrounding each cylinder bore. A
five-main-bearing crankshaft support structure is employed, with four
connecting rod journals positioned between five main bearings.
This arrangement provides the crankshaft support necessary for the
engine's 50 hp output and continuous duty cycle capability. The
deep-skirt block design extends below the crankshaft centerline,
enhancing structural rigidity under sustained load. The water jacket
surrounds the entirety of the cylinder bores to maximize heat transfer
away from the combustion zone. The cylinder block includes the timing
gear housing at the front, containing the gear train that drives the
camshaft, injection pump, and oil pump.
The cylinder head is a separate cast-iron component bolted to the top of
the cylinder block using a single-piece head gasket. The cylinder head
contains two valves per cylinder, one intake and one exhaust, for a
total of eight valves. The overhead valve (OHV) configuration uses
pushrods actuated by the camshaft located within the cylinder block.
The combustion chamber is formed partly in the cylinder head as a swirl
chamber (spherical or pear-shaped cavity) and partly in the piston
crown. This swirl chamber design produces intense air rotation during
the compression stroke, promoting complete mixing of fuel and air before
ignition. Valve lash adjustment is performed via set screws on the
rocker arms. Cold valve clearance specification for both intake and
exhaust valves is 0.25 mm (0.010 in).
The fuel system employs a mechanical indirect injection design with a
swirl combustion chamber. The injection pump is a Bosch PES4A65B type
in-line pump, a multi-plunger design where each cylinder has its own
pumping element. This pump configuration provides independent fuel
delivery adjustment for each cylinder. The pump is mounted on the side
of the cylinder block and driven by a gear train from the camshaft. A
mechanical or pneumatic governor controls engine speed.
Two governor options exist: a mechanical Bosch EP/RSV250 type or a
pneumatic Bosch EP/MZ60A type. The governor senses engine speed and
adjusts fuel delivery to maintain the selected governed speed under
varying loads. A fuel transfer pump mounted on the injection pump
housing draws fuel from the tank through a primary filter and water
separator. The injection pump pressurizes fuel and delivers it to
individual injection lines.
These steel lines carry high-pressure fuel to the Bosch DN40SD type
injection nozzles mounted in the cylinder head. Each nozzle directs fuel
into the swirl chamber, where initial combustion begins. The burning
gases then expand through a throat into the main cylinder. This
two-stage combustion process reduces peak cylinder temperatures and
pressures, lowering NOx emissions and combustion noise. An automatic
timer (autotimer) for fuel injection timing may be optional equipment. A
manual shutoff lever on the injection pump provides mechanical stopping
of the engine.
The lubrication system is a forced-feed, pressurized, wet-sump design.
The oil pump is a trochoid-type unit, driven directly by a gear on the
crankshaft. This pump design uses an inner rotor with lobes meshing with
an outer rotor, providing smooth, quiet oil delivery. A suction pipe
extends from the pump into the oil sump, drawing oil through a wire-mesh
strainer.
After pressurization, oil passes through a full-flow oil filter mounted
externally on the cylinder block. The filter element is a paper
cartridge type with a differential bypass valve that opens if the filter
becomes restricted. From the filter, oil travels through internal
drillings in the cylinder block to reach the five main bearings. Drilled
passages within the crankshaft direct oil from the main bearings to the
connecting rod bearings.
Excess oil from the main bearings and camshaft bearings is directed
upward through vertical passages to lubricate the valve train: camshaft
lobes, lifters, pushrod ends, rocker arms, and valve stems. The system
capacity is 6.0 liters (6.3 US qt). Operating oil pressure at rated
engine speed should register 2.8 bar to 3.2 bar (40 psi to 45 psi) with
the relief valve set at 3.0 ± 0.2 kg/cm2 (42.7 psi). A pressure relief
valve located near the oil pump outlet prevents excessive pressure
during cold starts.
The cooling system is a pressurized, pump-circulated water system. A
centrifugal water pump is belt-driven from the crankshaft pulley.
Coolant flows from the lower radiator hose into the water pump, through
the cylinder block water jacket, upward into the cylinder head, and then
out through the upper radiator hose. A wax-type thermostat regulates
operating temperature. The thermostat begins to open at 74.5°C to 78.5°C
(166°F to 173°F).
A bypass circuit allows coolant circulation within the engine block and
head when the thermostat is closed, preventing localized hot spots
during warm-up. The engine-only cooling system capacity, excluding the
radiator and external hoses, is 3.5 liters (3.7 US qt). A fan attached
to the water pump pulley draws air through the radiator core. For marine
applications, a heat exchanger replaces the radiator, using raw water
(seawater or river water) to cool the engine coolant through a
shell-and-tube heat exchanger.
| Intake and Exhaust Systems |
Air Intake System: Two air cleaner options are available: a dry type
with a paper filter element or an oil bath type with a pre-cleaner. The
intake manifold is a cast-iron component distributing air evenly to all
four cylinders.
Exhaust System: Exhaust gases exit each cylinder into the exhaust
manifold, which collects gases into a single pipe. An exhaust muffler
reduces noise emissions.
0The electrical system is 12-volt with negative ground as
standard equipment, with a 24-volt system offered as an option. A pinion
shift type starter motor, rated at 2.0 kW, engages with the flywheel
ring gear. A belt-driven alternator charges the battery. Sheathed-type
glow plugs provide cold starting assistance. One glow plug is installed
in the cylinder head for each cylinder. The glow plug specifications are
10.5V at 3.3A for the 12-volt system and 22.5V at 4.8A for the 24-volt
system.
The complete engine assembly, including the injection pump, manifolds,
alternator, starter, and flywheel housing, has an overall length of 650
mm (25.6 in), a width of 480 mm (18.9 in), and a height of 620 mm (24.4
in). The dry weight, excluding fluids but including all standard
engine-mounted accessories, is 200 kg (441 lb).
Service intervals for the 4DQ50 are based on operating hours. Engine oil
and filter should be changed every 250 hours under normal conditions.
For a new engine, change the oil after the initial 60 hours of
operation. Oil viscosity selection follows API service classification CD
or higher. Recommended viscosities are SAE 15W-40 for year-round use in
temperatures above -10°C (14°F) and SAE 10W-30 for winter operation.
The fuel filter requires replacement every 250 hours. The air cleaner
element requires cleaning every 100 hours and replacement every 500
hours. Valve lash adjustment is required every 250 hours. The cooling
system requires draining, flushing, and refilling with a fresh coolant
mixture every 1,000 hours or one year. Compression pressure should be
checked every 500 hours.
The standard compression pressure is above 25 kg/cm2 (355 psi) at 150 to
200 rpm cranking speed, with a minimum service limit of 20 kg/cm2 (284
psi). A compression pressure measurement below the service limit
indicates wear requiring overhaul. The injection pump timing should be
checked and adjusted every 1,000 hours. The fuel injectors require
testing and recalibration every 1,000 hours. Glow plug resistance should
be checked every 500 hours.
Cylinder head bolts receive a torque of 115 Nm to 122 Nm (85 lb-ft to 90
lb-ft). A crosswise tightening sequence from the center outward must be
followed. Connecting rod cap nuts are torqued to 52 Nm to 56 Nm (38
lb-ft to 41 lb-ft). Main bearing cap bolts receive a torque of 80 Nm to
85 Nm (59 lb-ft to 63 lb-ft). Flywheel bolts are torqued to 80 Nm to 85
Nm (59 lb-ft to 63 lb-ft). The crankshaft front pulley bolt is torqued
to 100 Nm (74 lb-ft).
The rocker arm shaft bracket nuts are secured to 25 Nm (18 lb-ft).
Intake manifold bolts receive 20 Nm (15 lb-ft). Exhaust manifold nuts
are torqued to 25 Nm (18 lb-ft). The injection pump mounting nuts
receive 20 Nm (15 lb-ft). The injector hold-down nuts are torqued to 25
Nm (18 lb-ft).
The oil filter canister requires tightening to 15 Nm (11 lb-ft) or
three-quarters of a turn after gasket contact. The oil drain plug is
torqued to 40 Nm (30 lb-ft). The water pump mounting bolts receive 15 Nm
(11 lb-ft). The glow plugs are torqued to 15 Nm (11 lb-ft). The starter
motor mounting bolts are torqued to 35 Nm (26 lb-ft). The alternator
mounting bolts receive 25 Nm (18 lb-ft).
The Mitsubishi 4DQ50 engine powers a wide range of industrial,
agricultural, and marine equipment. Primary forklift applications
include Mitsubishi-branded and J.I. Case-branded forklifts in the
2.5-ton to 3.5-ton capacity range. Construction equipment applications
include small excavators, compact loaders, and scissor lifts. Marine
propulsion applications include Dutch steel cruisers, barges, and river
cruisers such as the Vedette Hollandaise (1978), Friese Motortjalk
(1975-1980), and Bergermermeerkruiser 970 (1979). In marine service, the
engine is often badged as the Mitsubishi Samofa 4DQ50.
Marine installations use a heat exchanger cooling system with raw water
intake. Agricultural applications include small tractors and stationary
power units for irrigation pumps and grain dryers. Generator set
applications use the engine at its continuous power rating of 40 hp to
45 hp at 1,800 rpm for 60 Hz power or 1,500 rpm for 50 Hz power. The
4DQ50 is distinct from the smaller Mitsubishi 4DQ45 (1.9-liter) and the
larger 4DQ55 (2.4-liter) engines within the same QD series family. A
naturally aspirated variant with direct injection exists in other
markets, while the 4DQ50 is specifically the swirl chamber (indirect
injection) variant within the 4DQ series.
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