Mitsubishi K4N Specifications
| Engine Model: Mitsubishi K4N |
| Engine Type: 4-cycle inline 4-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 139.7 cu.in (2.29 L) |
| Rated Engine Power: 40-50 Hp (30-37 kW) at 2600 rpm |
| Fuel System Type: Indirect injection |
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The Mitsubishi K4N is a vertical, water-cooled,
4-stroke, 4-cylinder diesel engine with a displacement of 2.29 L (2,290
cc). It belongs to Mitsubishi's compact diesel engine family and is
recognized for its medium power output, fuel efficiency, and durability
in continuous operation. The K4N features an indirect injection (IDI)
combustion system and is naturally aspirated, relying on atmospheric
induction rather than forced aspiration. This engine configuration was
engineered to provide reliable power for heavy machinery applications,
including mini-excavators, wheel loaders, compact tractors, and
industrial generators.
The Mitsubishi K4N engine powers equipment from several manufacturers,
including the Caterpillar 305CR and Mitsubishi MM57SR mini-excavators,
as well as the Mitsubishi GX40 and GX46 agricultural tractors. In the
GX40 tractor, the engine produces 40 hp (29.8 kW) at 2,600 rpm, while
the GX46 delivers 46 hp (34.3 kW) at the same engine speed.
A K4N-powered Kobashi KS45 mini-excavator delivers 31.1 kW at 2,400 rpm,
demonstrating the engine's versatile power band across different
equipment types. The K4N is also found in Mitsubishi mini trucks, vans,
and small commercial vehicles across Asian markets. Its simple
mechanical fuel injection system enhances reliability in harsh, dusty,
or high-temperature environments, making it suitable for both commercial
and municipal applications in urban and rural settings.
Engine Type: 4-stroke, vertical, water-cooled, inline-4 diesel.
Displacement: 2.29 L (2,290 cc), 139.7 cu.in.
Bore x Stroke: 90.0 mm x 90.0 mm (3.54 in x 3.54 in).
Compression Ratio: 21:1.
Combustion System: Indirect injection (IDI).
Aspiration: Naturally aspirated.
Firing Order: 1-3-4-2.
Maximum Power: 40-50 hp (30-37 kW) depending on application.
Specific rating: 40 hp (29.8 kW) at 2,600 rpm for the GX40 tractor.
Specific ratings: 46 hp (34.3 kW) at 2,600 rpm for the GX46 tractor.
Maximum Torque: 100-110 Nm (74-81 lb-ft).
Rated Speed Range: 2,400-2,600 rpm depending on equipment.
Valvetrain: Overhead valve (OHV), 2 valves per cylinder (8 valves
total).
Fuel System: Mechanical indirect injection with in-line injection pump.
Injection Timing: 21° BTDC.
Idle Speed: 650-750 rpm.
Electrical System: 12 V with starter motor and alternator.
The cylinder block is constructed from cast iron, a material selected
for its high rigidity, excellent wear resistance, and dimensional
stability under sustained operational loads. The block features a
vertical, inline 4-cylinder configuration with a deep-skirt design
extending below the crankshaft centerline, providing enhanced support
for the main bearing webs and reducing vibration. Five main bearings
support the crankshaft, distributing the loads evenly across the
rotating assembly. The cylinder bores are machined directly into the
cast iron block. Replacement pistons are available in standard oversizes
to accommodate block reboring during rebuilds.
The block incorporates a full-length water jacket surrounding each
cylinder to maintain uniform operating temperatures and prevent
localized hot spots under continuous load conditions. Integrated oil
galleries are cast into the block structure to supply pressurized oil to
the main bearings, connecting rod bearings, and the valve train
components. The engine uses a rear-wheel-drive configuration with
bellhousing patterns compatible with various transmissions. The block
features mounting bosses for the starter motor, alternator, and other
accessories.
The cylinder head is manufactured from cast aluminum alloy and features
a cross-flow design for efficient gas exchange. The combustion chamber
is designed for indirect injection, incorporating a pre-combustion
chamber (swirl chamber) where fuel begins its combustion process before
expanding into the main cylinder. This IDI design promotes smoother
combustion, reduced noise, and improved performance at lower engine
speeds.
The valvetrain operates with an overhead valve (OHV) configuration using
pushrods and rocker arms actuated by a camshaft located in the cylinder
block. Each cylinder is served by two valves: one intake valve and one
exhaust valve. The valve stem seals are constructed from fluoroelastomer
material to prevent oil consumption past the valve guides. The valve
clearance requires periodic manual adjustment. The cold valve clearance
specification for both intake and exhaust valves is 0.25 mm (0.010 in).
The cylinder head is secured to the block using multiple head bolts
arranged around each cylinder bore, requiring a specific multi-stage
tightening sequence.
The fuel system on the K4N is an indirect injection (IDI) design with a
mechanical in-line injection pump. The injection pump is driven by the
engine's gear train and supplies fuel under high pressure to the
injection nozzles. Each cylinder is served by a separate injection line
connecting the pump to the nozzle, which is positioned in the
pre-combustion chamber within the cylinder head. The indirect injection
process begins with fuel injection into a swirl chamber, where partial
combustion occurs before the burning mixture expands into the main
cylinder.
The injection timing is set to 21° BTDC, a value that ensures complete
combustion and optimal power output while maintaining cold-start
capability. A mechanically governed injection pump maintains fuel
delivery rates corresponding to engine speed and load. The fuel system
includes a fuel filter with a water separator. The engine is compatible
with diesel fuel meeting standard specifications for naturally aspirated
indirect injection engines.
The lubrication system is a fully pressurized, wet-sump design. A
gear-type oil pump, driven from the crankshaft, draws oil from the oil
pan through a screened pickup tube. The oil is forced through a
full-flow spin-on oil filter before distribution to the main galleries.
From the main galleries, pressurized oil is supplied to the five main
bearings, four connecting rod bearings, camshaft bearings, and the valve
train components including the rocker arms and pushrods.
The recommended engine oil viscosity is 10W-30 or 10W-40 with an API
classification of CD or better. The total oil capacity is 5.5-6.0 L
(5.8-6.3 qt) including the oil filter. A dipstick provides a convenient
method for checking the oil level. The oil pressure relief valve
prevents over-pressurization at higher engine speeds. Regular oil and
filter changes are required at intervals specified by the equipment
manufacturer, with many applications recommending changes every 250-500
operating hours.
The cooling system is a pressurized, water-circulation design with a
cross-flow radiator. A centrifugal water pump, driven by a belt from the
crankshaft pulley, circulates coolant through the engine block and
cylinder head. Coolant flows from the water pump into the cylinder block
water jacket, surrounding the cylinder bores to extract heat from the
combustion chamber lower regions, then moves upward into the cylinder
head to cool the pre-combustion chambers and valve seats before exiting
through the thermostat housing.
A wax-type thermostat maintains engine operating temperature by
regulating coolant flow to the radiator. The thermostat begins to open
at 76-82 °C (169-180 °F). The total cooling system capacity varies by
equipment application but generally falls between 6.0-8.0 L (6.3-8.5
qt). A radiator fan, either engine-driven or electric depending on the
application, draws air through the radiator core to dissipate heat. The
system requires a 50/50 mixture of ethylene glycol antifreeze and
distilled water to prevent freezing, boiling, and corrosion.
Starting System: Starting is accomplished by an electric starter motor
engaging the flywheel ring gear. The starter motor is a 12 V unit with a
power rating of 2.0 kW. Glow plugs are installed in the cylinder head,
each positioned in the pre-combustion chamber. An electronic glow
control system activates the glow plugs before and during cranking for
cold-start assistance.
Electrical System: The engine is equipped with a 12 V charging system. A
belt-driven alternator with a rated output of 35-50 A provides
electrical power for the starter motor, glow plug system, and equipment
electrical systems. The battery must deliver sufficient cold cranking
amps for reliable starting in low temperatures.
Exhaust System: The exhaust manifold is a cast iron unit bolted to the
cylinder head. The engine meets EU Stage II / Tier 2 equivalent emission
standards through internal combustion optimization. No exhaust
aftertreatment systems such as Diesel Particulate Filters (DPF) or
Selective Catalytic Reduction (SCR) are required.
Engine Mass (Dry): 150-160 kg (330-353 lb) depending on accessory
configuration.
Overall Length: 650-700 mm (25.6-27.6 in).
Overall Width: 500-550 mm (19.7-21.7 in).
Overall Height: 650-700 mm (25.6-27.6 in).
Engine Oil Grade: 10W-30 or 10W-40, API classification CD or better.
Engine Oil Capacity: 5.5-6.0 L (5.8-6.3 qt) including filter.
Coolant Capacity: 6.0-8.0 L (6.3-8.5 qt) depending on radiator.
Coolant Type: Ethylene glycol antifreeze, 50/50 mixture with distilled
water.
Fuel System: Mechanical indirect injection, in-line injection pump.
Injection Timing: 21° BTDC.
Valve Clearance (Cold - Intake): 0.25 mm (0.010 in).
Valve Clearance (Cold - Exhaust): 0.25 mm (0.010 in).
Idle Speed: 650-750 rpm.
Rated Speed Range: 2,400-2,600 rpm.
Glow Plugs: 12 V, replaceable as a set.
Starter Motor: 12 V, 2.0 kW.
Cylinder Head Bolts (M14 - Step 1): 20 Nm (14.8 lb-ft).
Cylinder Head Bolts (M14 - Step 2): 40 Nm (29.5 lb-ft).
Connecting Rod Cap Nuts: 25 Nm (18.4 lb-ft).
Main Bearing Bolts: 30 Nm (22.1 lb-ft).
Flywheel Bolts: 83 Nm (61.2 lb-ft).
Intake Manifold Bolts: 20-25 Nm (14.8-18.4 lb-ft).
Exhaust Manifold Nuts: 25-30 Nm (18.4-22.1 lb-ft).
Oil Pan Bolts: 10-12 Nm (7.4-8.9 lb-ft).
Water Pump Bolts: 15-20 Nm (11.1-14.8 lb-ft).
Injection Lines (at nozzle and pump): 25 Nm (18.4 lb-ft).
Glow Plugs: 12-15 Nm (8.9-11.1 lb-ft).
The Mitsubishi K4N engine is used across a diverse range of equipment
categories and models.
Mini-Excavators:
Caterpillar 305CR.
Mitsubishi MM57SR.
Kobashi KS45 (31.1 kW at 2,400 rpm).
Compact Tractors:
Mitsubishi GX40 (40 hp / 29.8 kW at 2,600 rpm).
Mitsubishi GX46 (46 hp / 34.3 kW at 2,600 rpm).
Mini Trucks and Commercial Vehicles:
Mitsubishi Minicab Truck.
Mitsubishi Minicab Van.
Mitsubishi Canter (various years).
Industrial Equipment:
Wheel loaders.
Road sweepers (municipal cleaning vehicles).
Portable generators (mobile power units for construction sites).
The Mitsubishi K4N was produced over several decades, with the naturally
aspirated indirect injection version being the most common configuration
used in construction and agricultural machinery. The engine's simple
mechanical fuel system and robust construction have contributed to its
popularity in regions where parts availability and mechanic familiarity
are essential. With proper care, these engines often exceed 300,000 km
or several thousand operating hours before requiring a major overhaul.
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