Mitsubishi K3G Specifications
| Engine Model: Mitsubishi K3G |
| Engine Type: 4-cycle inline 3-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 75.4 cu.in (1.23 L) |
| Rated Engine Power: 25 Hp (19 kW) at 2600 rpm |
| Fuel System Type: Direct injection |
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The Mitsubishi K3G is a 1.2-liter, naturally
aspirated, three-cylinder diesel engine manufactured by Mitsubishi Heavy
Industries. This powerplant belongs to the Mitsubishi K-series engine
family, a platform engineered for compact agricultural equipment, small
construction machinery, and industrial power applications. The K3G
represents a larger bore variant within the K3 series, distinguished by
its direct injection (DI) combustion system featuring bowl-top pistons.
The engine operates on a four-stroke, compression-ignition cycle with a
vertical, water-cooled inline configuration. The direct injection
combustion system delivers fuel directly into a recessed bowl machined
into the piston crown, improving thermal efficiency and fuel economy
compared to indirect injection designs. Mitsubishi engineered the K3G
with a Bosch M-type in-line injection pump and throttle-type injection
nozzles, providing precise fuel metering for the 20 to 25 horsepower
output range.
The engine carries a standard compression pressure specification of 30
kg/cm2 at a cranking speed of 280 rpm, demonstrating the sealing
integrity of the piston rings and valve seats. The K3G is installed in
compact tractors such as the Cub Cadet 7232 and 7234, the Case IH 1130,
and the Mitsubishi MM35 mini excavator, as well as in the Mitsubishi
MT205 compact utility tractor, where it delivers dependable service at a
rated speed of 2,500 rpm.
The Mitsubishi K3G is a four-stroke, compression-ignition, inline
three-cylinder diesel engine. The induction system is naturally
aspirated without turbocharging or supercharging equipment. Total
displacement measures 1,236 cc, equivalent to 75.4 cubic inches. The
bore dimension is 82 mm (3.23 in), and the stroke dimension is 78 mm
(3.07 in).
The standard compression pressure value of 30 kg/cm2 (427 psi) at 280
rpm provides a functional reference for engine health assessment. The
firing order sequence is 1-3-2, a configuration providing acceptable
balance for a three-cylinder engine. Maximum power output ranges from 15
kW to 19 kW, equivalent to 20 hp to 25 hp, at a rated engine speed of
2,500 rpm. The combustion system is direct injection with bowl-top
pistons.
The cylinder block is constructed from cast iron, providing rigidity,
vibration damping, and wear resistance required for prolonged service in
agricultural and construction environments. The block is an inline
three-cylinder design with integral cylinder bores machined directly
into the casting.
A four-main-bearing crankshaft support structure is employed, with three
connecting rod journals positioned between four main bearings to provide
adequate support for the engine's torque output. The deep-skirt block
design contributes to structural rigidity and noise reduction. The water
jacket surrounds the entirety of the cylinder bores to maximize heat
transfer away from the combustion zone.
The cylinder head is a separate cast-iron component bolted to the top of
the cylinder block. The cylinder head contains two valves per cylinder,
one intake and one exhaust, for a total of six valves. The combustion
chamber is formed partly in the cylinder head and partly as a recessed
bowl machined directly into the piston crown, a defining feature of the
direct injection system.
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 (0.0098 in). The valve seat angles are 45 degrees. The cylinder
head gasket is a composite or multi-layer steel design depending on the
production year.
The fuel system employs a mechanical direct injection design. The
injection pump is a Bosch M-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 flyweight governor, internal to
the injection pump, senses engine speed and adjusts fuel delivery to
maintain the selected governed speed under varying loads.
The governor incorporates both low-idle and high-speed limiting control
circuits. A fuel transfer pump, mounted on the injection pump housing,
draws fuel from the tank through a primary filter and water separator.
The transfer pump delivers fuel at low pressure to the injection pump
inlet. The injection pump pressurizes fuel and delivers it to individual
injection lines. These steel lines carry high-pressure fuel to the
throttle-type injection nozzles mounted in the cylinder head.
The throttle-type nozzle uses a pintle that lifts off its seat under
fuel pressure, with the pintle shape providing an initial throttling
effect that reduces the quantity of fuel injected at the beginning of
the injection event, softening combustion noise. The nozzle sprays fuel
directly into the bowl-top recess on the piston crown, where the fuel
mixes with compressed, heated air and auto-ignites. A manual shutoff
lever on the injection pump provides mechanical stopping of the engine.
Excess fuel not injected returns to the fuel tank via a low-pressure
return line.
The lubrication system is a pressurized, wet-sump design using a
gear-type or trochoid-type oil pump. The oil pump is driven directly by
a gear on the crankshaft and is located inside the timing cover or oil
pan depending on the specific variant. 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 spin-on, replaceable canister type. From the
filter, oil travels through internal drillings in the cylinder block to
reach the 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.
The system capacity, including the oil filter, is approximately 4.0
liters (1.05 US gal). The standard oil clearance for the connecting rod
big end bearing is 0.025 mm to 0.080 mm. 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-pellet thermostat regulates
operating temperature. The rated opening temperature is 76.5°C to 80.0°C
(170°F to 176°F) depending on the application.
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 3.0 liters (0.79 US gal). A fan attached
to the water pump pulley draws air through the radiator core. The
radiator is sized for operation in ambient temperatures up to 40°C
(104°F) under normal operating conditions.
| Intake and Exhaust Systems |
Air Intake System: Air enters through a dry-type or oil-bath air
cleaner, depending on the application and production year. The intake
manifold is a cast-iron component distributing air evenly to all three
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.
Electrical System: The electrical system is 12-volt with negative
ground. A starter motor rated at 1.6 kW engages with the flywheel ring
gear. A belt-driven alternator charges the battery, with a minimum
battery capacity recommendation of 60 ampere-hours. A glow plug system
provides cold starting assistance. One glow plug is installed in the
cylinder head for each cylinder.
Starting Aid: The glow plug system includes an indicator lamp on the
equipment dashboard. Preheat time ranges from 5 to 15 seconds depending
on ambient temperature.
The complete engine assembly, including the injection pump, manifolds,
alternator, starter, and flywheel housing, has an overall length of 550
mm (21.7 in), a width of 420 mm (16.5 in), and a height of 600 mm (23.6
in). The dry weight, excluding fluids but including all standard
engine-mounted accessories, is 145 kg (320 lb).
Service intervals for the K3G are based on operating hours. Engine oil
and filter should be changed every 150 hours under normal conditions and
every 100 hours under severe duty. Oil viscosity selection follows API
service classification CF or higher. Recommended viscosities are SAE
15W-40 for year-round use and SAE 10W-30 for winter operation.
The fuel filter requires replacement every 400 hours. The air cleaner
element requires cleaning every 100 hours and replacement every 400
hours. Valve lash adjustment is required every 400 hours. The cooling
system requires draining, flushing, and refilling with a fresh coolant
mixture every 1,000 hours or one year.
The compression pressure should be checked every 500 hours; the standard
value is 30 kg/cm2 (427 psi) at 280 rpm cranking speed. A compression
pressure measurement below 20 kg/cm2 (284 psi) 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.
Cylinder head bolts receive a torque of 130 Nm to 137 Nm (94 lb-ft to
101 lb-ft), equivalent to 12 kgm to 13 kgm. A crosswise tightening
sequence from the center outward must be followed. Connecting rod cap
nuts are torqued to 54 Nm to 58 Nm (40 lb-ft to 43 lb-ft), equivalent to
3.2 kgm to 3.5 kgm. Main bearing cap bolts receive a torque of
approximately 103 Nm (76 lb-ft), equivalent to 10.5 kgm.
Flywheel bolts are torqued to approximately 83 Nm (61.5 lb-ft),
equivalent to 8.5 kgm. 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 K3G engine powers a range of compact agricultural,
construction, and industrial equipment. Primary tractor applications
include the Mitsubishi MT205 compact utility tractor, where the engine
produces 20 hp at 2,500 rpm with a displacement of 75.4 cubic inches and
liquid cooling. The Cub Cadet 7232 and 7234 compact tractors utilize the
K3G as their standard power unit.
The Case IH 1130 compact tractor is equipped with this engine.
Construction equipment applications include the Mitsubishi MM35 mini
excavator. The engine is also found in compact skid steer loaders and
small generator sets from various manufacturers.
The K3G is distinct from the smaller Mitsubishi K3C and K3D engines,
which share the same three-cylinder configuration but differ in bore and
stroke dimensions. A naturally aspirated variant with indirect injection
exists as the Mitsubishi K3F, while the K3G is specifically the direct
injection variant within the K3 series.
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