Mitsubishi K3B Specifications
| Engine Model: Mitsubishi K3B |
| Engine Type: 4-cycle inline 3-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 51.8 cu.in (0.85 L) |
| Rated Engine Power: 15 Hp (11.2 kW) at 2000 rpm |
| Fuel System Type: Indirect injection |
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The Mitsubishi K3B is a vertical, water-cooled,
four-stroke, three-cylinder diesel engine with a displacement of 0.849
liters (849 cc). Part of Mitsubishi’s K-series engine family, this
compact power unit was engineered for agricultural and construction
machinery applications where reliability, fuel efficiency, and a small
installation footprint are prioritized. The K3B utilizes a swirl chamber
(indirect injection) combustion system, a design that provides smooth
operation, reduced combustion noise, and good low-speed torque
characteristics essential for compact tractors and mini excavators.
The engine features a cast iron cylinder block, an overhead valve (OHV)
valvetrain with two valves per cylinder, and a mechanical fuel injection
system with a Bosch M-type injection pump. Produced from the 1980s
onward, the K3B became a widely used diesel engine due to its
combination of power output and compactness, finding applications in
small tractors including the Iseki TX1410, TX145, TU1400, TU120, TU130,
and the Bobcat X120 mini excavator.
The Mitsubishi K3B is a four-stroke, water-cooled diesel engine
operating on the compression-ignition principle. The engine architecture
is an inline three-cylinder configuration with a total displacement of
849 cc (51.8 cu.in), derived from a bore of 68 mm (2.68 in) and a stroke
of 78 mm (3.07 in). This undersquare design, with stroke exceeding bore,
promotes torque generation at low engine speeds, a characteristic
essential for agricultural equipment requiring sustained pulling power
at reduced engine speeds. The compression ratio is set at 23.0:1, a
relatively high value for an indirect injection diesel engine, ensuring
reliable cold-start performance and efficient combustion.
The valvetrain utilizes an overhead valve (OHV) configuration with the
camshaft located in the cylinder block, driven by a gear train. Each
cylinder utilizes two valves - one intake and one exhaust - actuated via
pushrods and rocker arms. The firing order for this three-cylinder
engine is 1-3-2. The rated speed is 2,600 rpm, with maximum power
achieved at this engine speed. Performance outputs for the K3B reflect
its application in compact machinery. Maximum power is rated at 10.9 kW
to 11.2 kW (14.6 hp to 15.0 hp) at 2,600 rpm. Maximum torque is 45 Nm to
50 Nm (33 lb-ft to 37 lb-ft) at 1,800 rpm to 2,000 rpm.
The cylinder block is manufactured from cast iron, a material chosen for
its rigidity, wear resistance, and durability under the compression
pressures of diesel operation. The block features a deep-skirt design
providing structural stiffness for the three-cylinder configuration. The
cylinder bores are cast directly into the block and are finished with a
plateau honing process that optimizes oil retention and piston ring
sealing.
The block incorporates replaceable dry-type cylinder liners, allowing
for overhaul without replacing the entire block. The crankcase is
reinforced with webbing between cylinder bores to minimize distortion
under thermal and mechanical stress. The main bearing caps are secured
with two bolts per cap. The cylinder block incorporates the front gear
housing, which contains the camshaft drive gears and injection pump
drive gear.
The cylinder head is manufactured from cast iron, matching the cylinder
block material to ensure uniform thermal expansion. The head features an
overhead valve (OHV) configuration with the camshaft housed in the
cylinder block. The combustion chambers are of the indirect injection
swirl chamber design, where a pre-chamber (swirl chamber) promotes
thorough mixing of fuel and air before ignition, providing smoother
combustion and reduced diesel knock.
Each cylinder utilizes two valves - one intake and one exhaust -
arranged in a cross-flow configuration. The valves are actuated by
rocker arms mounted on a rocker shaft, with pushrods transmitting motion
from the camshaft to the rocker arms. Valve clearances require periodic
mechanical adjustment using an adjusting screw and locknut on the rocker
arm. The cold valve clearance is set at 0.25 mm (0.0098 in) for both
intake and exhaust valves. The valve seat inserts are manufactured from
heat-resistant alloys for diesel operation durability. The cylinder head
gasket is a composite or multi-layer steel (MLS) design.
The Mitsubishi K3B is equipped with a mechanical indirect injection
(IDI) fuel system. A Bosch M-type in-line injection pump is mounted on
the side of the cylinder block and driven by the front gear train. The
injection pump features a mechanical centrifugal flyweight governor that
controls fuel delivery based on engine speed and load. The pump includes
a manual cold-start advance mechanism that adjusts injection timing for
improved cold-start performance. The injection start pressure is set at
120 kg/cm2 (approximately 11.8 MPa / 1,710 psi) for the throttle-type
nozzles used in this series.
The injection lines are high-pressure steel tubes routed individually
from the injection pump to the injectors mounted in the cylinder head.
The injectors are of the nozzle-and-holder type with throttle-type
nozzles, incorporating a spring-loaded pintle nozzle that opens at the
predetermined pressure, atomizing the fuel into the swirl chamber. The
injection timing is set at 15 degrees BTDC for standard operation. The
fuel filtration system includes a primary water separator and a
secondary replaceable fuel filter to protect the injection pump and
injectors from contamination. A manual primer pump is incorporated into
the fuel system to facilitate bleeding of air.
The lubrication system is a forced-feed, full-flow filtration design
utilizing a trochoid-type oil pump. The trochoid pump, known for its
compact design and quiet operation, draws lubricant from the sump
through a strainer and delivers it to the main oil gallery. The system
maintains stable oil pressure across the operating range, with a
pressure relief valve calibrated to open at 3.5 bar to 4.0 bar (51 psi
to 58 psi).
The engine employs a full-flow paper element oil filter mounted on the
cylinder block. The oil pan capacity is 3.0 liters (3.2 US qt) total
upper limit. The engine requires SAE 10W-30 or 5W-30 engine oil meeting
API service classification CD or higher specification.
The cooling system is a pressurized, water-cooled design utilizing a
centrifugal water pump driven by the accessory drive belt. The system
maintains engine operating temperature within a range of 80°C to 90°C
(176°F to 194°F) under normal conditions. The coolant circuit includes a
thermostatic bypass that facilitates rapid warm-up and reduces internal
friction during cold starts.
The water pump is mounted on the front of the engine block. A cross-flow
radiator with an electric or mechanical fan supplements the system at
low engine speeds and during idle conditions. The engine block coolant
capacity is 3.0 liters (3.2 US qt), excluding the radiator and hoses.
The total coolant capacity for the complete system varies by equipment
application.
Air Intake: The intake system incorporates a cast iron intake manifold
designed for durability in agricultural environments. Air is drawn
through a heavy-duty paper element air cleaner before entering the
intake manifold. The engine is naturally aspirated in its standard
configuration.
Engine Management: The K3B utilizes no electronic engine management
system. Fuel delivery is controlled mechanically by the injection pump
governor. The electrical system consists of a 12V starter motor rated at
1.6 kW and a 12V alternator rated at 15 A or 35 A depending on the
application.
Glow Plug System: The engine is equipped with glow plugs installed in
each cylinder head to assist with cold starting. The glow plugs are
energized through a glow controller that activates them based on ambient
temperature and coolant temperature. Glow plug tightening torque is 15
Nm to 20 Nm (11 lb-ft to 15 lb-ft).
Exhaust System: The exhaust system incorporates a cast iron exhaust
manifold merging into a single exhaust pipe. The system includes a
muffler.
The overall dimensions vary by application configuration. The dry weight
is 90 kg to 100 kg (198 lb to 220 lb) depending on accessory fitment.
The starter motor dimensions are 220 mm x 150 mm (8.66 in x 5.91 in)
with a mounting hole spacing of 115 mm (4.53 in) and mounting screw hole
diameter of 10.70 mm (0.421 in).
The service life of the K3B under proper operating conditions is
engineered to exceed 8,000 operating hours in agricultural applications
with regular maintenance. Oil change intervals are recommended at 150
operating hours for severe service conditions or 250 hours under normal
operating conditions. The engine requires SAE 10W-30 or 5W-30 engine oil
meeting API CD or higher specification.
Valve clearance inspection and adjustment is mandated every 500
operating hours. The intake and exhaust valve clearances are both set at
0.25 mm (0.0098 in) cold. Replacement of the fuel filter is required
every 500 operating hours or 12 months.
The air cleaner element requires replacement based on operating
environment dust loading, with inspection at 100-hour intervals. The
coolant must be replaced every 2 years or 1,000 operating hours. The
accessory drive belt requires inspection at each service interval, with
replacement when cracking or wear is evident.
Critical fasteners on the K3B require precise torque application. The
cylinder head bolts are torqued to 130 Nm to 137 Nm (94 lb-ft to 101
lb-ft). The connecting rod cap nuts are torqued to 40 Nm to 43 Nm (30
lb-ft to 32 lb-ft). The main bearing cap bolts are torqued to 50 Nm to
60 Nm (37 lb-ft to 44 lb-ft).
The flywheel-to-crankshaft bolts receive a torque of 70 Nm to 80 Nm (52
lb-ft to 59 lb-ft). The rocker arm shaft pedestal bolts are torqued to
25 Nm to 30 Nm (18 lb-ft to 22 lb-ft). The injection pump drive gear
bolt is torqued to 50 Nm (37 lb-ft). The injector hold-down nuts are
torqued to 20 Nm to 25 Nm (15 lb-ft to 18 lb-ft).
The glow plugs are torqued to 15 Nm to 20 Nm (11 lb-ft to 15 lb-ft). The
intake and exhaust manifold bolts are torqued to 20 Nm to 25 Nm (15
lb-ft to 18 lb-ft). These values assume the use of high-strength,
lubricated threads as per factory specifications.
The Mitsubishi K3B was utilized across a broad range of compact
agricultural and construction equipment. In the agricultural tractor
segment, the engine powered small tractors including the Iseki TX1410,
TX145, TX2140, TU120, TU130, and TU1400 models. The engine was also used
in the Iseki TX155 and Suzue M1503 tractors, where the K3B provided 14.6
hp to 15.0 hp of power.
In the construction equipment sector, the K3B was installed in mini
excavators including the Bobcat X120, where the engine’s compact
dimensions and reliable power delivery were valued for tight-quarter
excavation work. The K3B also found application in other
Mitsubishi-branded agricultural machinery including the MT180, MT180D,
MT1401D, MT1601D, MT20MS4, MT205M, MT470D, and MTE1800 tractor models.
The engine was also available as a replacement power unit for various
equipment types, supplied with a 3-month warranty through aftermarket
parts distributors. The K3B remains in service across a substantial
installed base of equipment and continues to be supported through
aftermarket parts channels.
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