Mitsubishi K4C Specifications
| Engine Model: Mitsubishi K4C |
| Engine Type: 4-cycle inline 4-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 73.2 cu.in (1.2 L) |
| Rated Engine Power: 30 Hp (22 kW) at 2600 rpm |
| Fuel System Type: Indirect injection |
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The Mitsubishi K4C is a vertical, water-cooled,
four-cycle, four-cylinder inline diesel engine with a displacement of
1.200 liters (1200 cc). Part of the K-series family, this engine was
engineered for compact industrial and construction machinery. Its robust
design and compact dimensions made it a preferred powerplant for
applications requiring reliability under continuous operation, such as
wheel loaders, mini-excavators, and agricultural tractors including the
Mitsubishi D2350, ST2320, and MT2501.
The K4C employs an indirect injection (IDI) combustion system, which
contributes to smoother running and reduced mechanical noise compared to
direct injection engines of its era. The engine's construction follows
Mitsubishi's established K-series architecture, featuring a cast iron
cylinder block, an aluminum rocker cover, and a Bosch M-type mechanical
fuel injection system.
While its power output of approximately 27 hp (20 kW) is modest by
modern standards, the K4C remains widely respected for its longevity,
ease of maintenance, and parts availability across global markets for
vintage machinery restoration and ongoing operation.
The Mitsubishi K4C is a four-cycle, water-cooled, inline four-cylinder
diesel engine. The cylinder bore measures 70.0 mm (2.76 in), while the
piston stroke extends to 78.0 mm (3.07 in), producing an undersquare
configuration that favors torque production at lower engine speeds.
Total displacement is 1,200 cc (1.200 L / 73.2 cu.in). The compression
ratio for the K-series diesel family is 22.0:1, though exact figures
vary by specific sub-variant and injector calibration. The firing order
is 1-3-4-2, standard for Mitsubishi four-cylinder K-series engines.
Maximum power output is 20-22 kW (27-30 hp) at 2,400-2,600 rpm,
depending on the specific governor setting and application. Peak torque
is estimated at 80-85 Nm (59-63 lb-ft) between 1,600 and 1,800 rpm. Low
idle speed is set to 750-800 rpm, with a governed high idle of 2,800
rpm. The combustion system is indirect injection (IDI) with a
pre-combustion chamber design. The engine is naturally aspirated, with
no turbocharger or aftercooler present on standard K4C configurations.
The cylinder block is constructed from cast iron, providing the rigidity
necessary for sustained operation under variable industrial loads. The
block features a conventional inline-four configuration with cylinders
cast directly into the iron matrix. Unlike larger diesel engines, the
K4C does not utilize replaceable wet cylinder liners; the bores are
machined directly into the block casting. The cylinder bore surface is
hardened through a plateau honing process. The block incorporates five
main bearing bulkheads supporting the crankshaft.
An oil gallery is drilled along the right side of the block to supply
pressurized oil to the main bearings, camshaft bearings, and rocker arm
assembly. The water jacket surrounds the cylinders and extends upward to
the block deck. The engine number is stamped on a machined pad located
on the intake side of the block. Freeze plugs are pressed into the block
at four locations. The crankcase is of the deep-skirt design, extending
below the crankshaft centerline to enhance structural rigidity.
The cylinder head is manufactured from cast iron, a material selected
for its thermal stability and resistance to warpage under the thermal
cycling common in air-cooled and liquid-cooled industrial engines. The
head employs an overhead valve (OHV) configuration with two valves per
cylinder, for a total of eight valves. The valvetrain is actuated by a
camshaft located within the cylinder block, driving pushrods, rocker
arms, and valve stems. The intake valve head diameter measures 34.0 mm
(1.34 in), while the exhaust valve head diameter is 30.0 mm (1.18 in).
Valve stems are 7.0 mm (0.276 in) in diameter. The cylinder head
features pressed-in replaceable valve guides. Valve seat inserts are
induction-hardened for intake ports and made of heat-resistant alloy for
exhaust ports. Valve lash is adjusted with the engine cold using a
feeler gauge between the rocker arm and valve stem. Intake valve
clearance is set to 0.25 mm (0.010 in), and exhaust valve clearance is
also 0.25 mm (0.010 in).
The cylinder head gasket is a composite steel-asbestos design on early
engines, replaced by a fiber composite gasket on later production.
Cylinder head bolts are of two sizes: M12 big bolts with a torque
specification of 118-127 Nm (87-94 lb-ft) and M10 small bolts with a
torque specification of 78-88 Nm (58-65 lb-ft).
The fuel system employs indirect injection with a swirl pre-combustion
chamber design. A Bosch M-type in-line mechanical injection pump is
mounted to the right side of the engine block, gear-driven from the
camshaft. The injection pump is equipped with a mechanical flyweight
governor to maintain engine speed under varying loads. Injection
pressures range from 100 to 120 bar (1,450 to 1,740 psi) depending on
engine speed.
Each cylinder is served by an individual injection line connecting the
pump to a throttle-type nozzle holder assembly. The injectors feature
pintle-type nozzles with an opening pressure set to 115 bar (1,668 psi).
A gear-type transfer pump, integrated into the injection pump housing,
draws fuel from the tank through a primary filter with a water
separator.
A secondary spin-on fuel filter of 5-micron rating is located between
the transfer pump and the injection pump. Static injection timing is set
to 8-10° before top dead center (BTDC), measured at the injection pump
drive shaft. A hand primer pump on the secondary filter head allows
system priming after filter replacement.
The lubrication system is a fully pressurized, wet-sump design utilizing
forced lubrication via a trochoid-type pump. The oil pump is driven
directly by the crankshaft and is mounted inside the oil pan on the rear
main bearing cap. Oil pressure at rated engine speed (2,400-2,600 rpm)
is maintained between 30 and 50 psi (207 and 345 kPa). Total oil
capacity, including the oil filter, ranges from 4.0 to 4.5 L (4.2 to 4.8
U.S. qt) depending on the oil pan configuration for the specific
application.
A spin-on full-flow oil filter is mounted to the engine block on the
intake side. The system incorporates a bypass valve that opens at 25 psi
(172 kPa) differential pressure if the filter becomes restricted. The
oil pump relief valve is set to 60 psi (414 kPa).
The oil pan is constructed from stamped steel. A dipstick is located on
the intake side of the block. Recommended oil viscosity is SAE 15W-40 or
SAE 10W-30 meeting API CD or higher diesel rating. Piston cooling jets
are not present on the K4C; piston cooling relies on splash lubrication
from the connecting rod oil passages.
The cooling system is a pressurized, liquid-cooled design with a
belt-driven centrifugal water pump. The pump circulates coolant through
the cylinder block, upward into the cylinder head, and through the
radiator. Coolant capacity for the engine alone, without the radiator,
is 3.5 L (3.7 U.S. qt). A wax-pellet thermostat, rated at 76-82°C
(169-180°F), controls coolant flow to the radiator. A bypass circuit
allows coolant circulation inside the engine when the thermostat is
closed.
The radiator cap pressurizes the system to 88-108 kPa (12.8-15.7 psi).
An electric or belt-driven fan is mounted to the water pump hub
depending on the equipment application. The water pump shaft is sealed
with a carbon-ceramic seal. Coolant recommendations call for a 50/50
mixture of ethylene glycol antifreeze and distilled water. Freeze plugs
are installed at four locations on the block.
Electrical System: The electrical system operates at 12 volts. The
starter motor is a gear-reduction type with a solenoid-actuated pinion
engaging the flywheel ring gear. Starter motor power rating is 1.6 kW
(2.1 hp). The alternator is a brushless, internally regulated unit rated
at 35 amperes.
Exhaust System: The exhaust manifold is a single-piece, cast iron
log-type design merging the four cylinders into a single outlet. The
manifold outlet is flanged for connection to a muffler and exhaust pipe.
The complete engine dry weight without accessories is 95-110 kg (209-242
lb) depending on the specific application configuration. Overall engine
length, measured from the front crankshaft pulley to the flywheel
housing mounting face, is 520 mm (20.5 in). Maximum width, measured
across the injection pump and exhaust manifold, is 480 mm (18.9 in).
Height, from the oil pan rail to the top of the rocker arm cover, is 610
mm (24.0 in). The flywheel housing conforms to a Mitsubishi-specific
bolt pattern.
Engine oil and oil filter change intervals are recommended every 150
operating hours or six months under normal industrial conditions. The
fuel filter is replaced every 200 hours. The air cleaner element is
replaced every 100 hours in dusty environments. Valve lash inspection
and adjustment at 0.25 mm (0.010 in) for both intake and exhaust are
performed every 200 hours.
Coolant replacement is required every 1,000 hours or 24 months. Glow
plugs are inspected every 500 hours. The injection pump timing is
checked every 1,000 hours. The water pump is inspected annually. Piston
ring end gap for new rings is 0.20-0.35 mm (0.008-0.014 in) for
compression rings and 0.25-0.40 mm (0.010-0.016 in) for oil rings.
Cylinder Head Bolts (M12, large): 118-127 Nm (87-94 lb-ft)
Cylinder Head Bolts (M10, small): 78-88 Nm (58-65 lb-ft)
Connecting Rod Cap Nuts: 49-54 Nm (36-40 lb-ft)
Main Bearing Cap Bolts: 100-105 Nm (74-77 lb-ft)
Flywheel Bolts: 80-85 Nm (59-63 lb-ft)
Rocker Arm Shaft Bolts: 20-25 Nm (15-18 lb-ft)
Intake Manifold Nuts: 20-25 Nm (15-18 lb-ft)
Exhaust Manifold Nuts: 25-30 Nm (18-22 lb-ft)
Injector Hold-down Bolts: 25-30 Nm (18-22 lb-ft)
Glow Plugs: 15-20 Nm (11-15 lb-ft)
Oil Pan Bolts: 10-15 Nm (7-11 lb-ft)
Water Pump Bolts: 15-20 Nm (11-15 lb-ft)
Crankshaft Pulley Bolt: 120-130 Nm (89-96 lb-ft)
Injection Pump Drive Gear Nut: 40-45 Nm (30-33 lb-ft)
The Mitsubishi K4C engine was utilized across multiple industrial,
construction, and agricultural platforms.
Agricultural Tractors: Mitsubishi D1650, ST1620, ST1640, D1850, ST1820,
ST1840, D2050, ST2020, ST2040, D2350, ST2320, ST2340, MT1801, MT2001,
MT2201, MT2501, S670.
Wheel Loaders: Compact wheel loaders requiring 20-30 hp class engines.
Mini Excavators: Small excavators, including units from manufacturers
such as Seisakusho.
Skid Steer Loaders: Compact loaders requiring a 1.2-liter diesel
powerplant.
Dumpers: Seisakusho DW 10 dumper.
Aerial Platforms: Seisakusho aerial work platforms (K4C-31HL variant).
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| Outboard Engines Technical Specifications |
