Isuzu 3KR1 Specifications
| Engine Model: Isuzu 3KR1 |
| Engine Type: 4-stroke in-line 3-cylinder liquid-cooled diesel |
| Total Displacement: 84.9 cu.in (1.39 L) |
| Rated Engine Power: 27-30 Hp (20-22 kW) at 2800 rpm |
| Fuel System Type: Indirect injection |
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The Isuzu 3KR1 is a 1.4-liter, naturally
aspirated, three-cylinder diesel engine from Isuzu’s compact KR series,
engineered for high-performance industrial applications. Unlike many
automotive-focused diesel engines, the 3KR1 was designed to power large
refrigeration units (such as Thermo King RD-II, TD-II, and SB-II
models), mini excavators (including Hitachi EX and Sumitomo units), and
heavy-duty generators.
The engine features a heavy-duty cast iron block and an indirect
injection swirl chamber combustion system, prioritizing durability and
long continuous run times over peak power output. The 3KR1 employs a
mechanical Bosch-type PFR series in-line injection pump, contributing to
its reputation for simplicity and reliability in remote or
resource-limited operating environments. The engine’s compact
three-cylinder layout provides a balance between power delivery and fuel
efficiency for industrial duty cycles.
The 3KR1 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 1,391 cc (1.4
L / 84.9 cu.in), derived from a bore of 81 mm (3.19 in) and a stroke of
90.2 mm (3.55 in). This undersquare design, with stroke exceeding bore,
promotes torque generation at low engine speeds, a characteristic
essential for industrial applications requiring sustained pulling or
pumping power. The compression ratio is set at 20.0:1, a value that
ensures reliable cold-start capability and efficient combustion in the
indirect injection system.
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, producing uneven firing intervals of 240 degrees of
crankshaft rotation, a characteristic inherent to three-cylinder
designs. The rated speed is governed at 2,800 rpm, with maximum power
and torque peaks occurring within the lower to mid-range of the
operating band to preserve longevity in continuous industrial service.
Performance outputs for the 3KR1 are modest by automotive standards but
appropriate for its industrial applications. Maximum power ranges from
20 kW to 22 kW (27 hp to 30 hp) at 2,800 rpm. Maximum torque is 78.5 Nm
(57.9 lb-ft) at 1,800 rpm. The idle speed range is 800 rpm to 1,000 rpm.
Injection timing is specified at 15 degrees before top dead center
(BTDC). The engine is designed for continuous duty cycles, including
extended idling and variable load conditions common in refrigeration and
generator applications.
The cylinder block is manufactured from cast iron with a heavy-duty
construction, providing the exceptional rigidity and wear resistance
required for high-cycle industrial operation. The block features a cast
iron crankcase reinforced with webbing between cylinder bores to
minimize distortion under sustained thermal and mechanical stress. 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 service wear limit for the cylinder bore is 81.2 mm (3.20 in), with
the original bore diameter of 81 mm (3.19 in). The replaceable wet-type
cylinder liners are fitted with pistons having a diameter of 80.89 mm to
80.93 mm (3.185 in to 3.186 in), with a piston clearance of 0.07 mm to
0.11 mm (0.0028 in to 0.0043 in). The main bearing caps are manufactured
from nodular cast iron and are secured with bolts torqued to
specifications appropriate for the engine’s output.
The cylinder head is manufactured from cast iron, matching the cylinder
block material to ensure uniform thermal expansion across the engine.
The head features an overhead valve (OHV) configuration with the
camshaft housed in the cylinder block. The combustion chambers are of
the indirect injection (IDI) design, incorporating swirl chambers that
promote 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 0.40 mm (0.016 in) for both
intake and exhaust valves. The valve seat inserts are manufactured from
heat-resistant alloys selected for diesel operation durability.
The 3KR1 is equipped with a mechanical indirect injection (IDI) fuel
system utilizing a Bosch-type PFR series in-line injection pump. This
pump was also supplied by Zexel under cross-reference numbers
104134-3021 and 8970103841. The mechanical injection pump is driven by
the engine’s gear train and features a mechanical 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 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, incorporating a
spring-loaded pintle nozzle that opens at a 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 gear-type oil pump. The system maintains stable oil pressure
within a range of 3.0 bar to 5.0 bar (44 psi to 73 psi) at 3,000 rpm. An
oil cooler is not fitted in standard configurations, though the engine
design accommodates one for certain industrial variants.
The engine employs a full-flow spin-on oil filter mounted on the
cylinder block. The oil pan capacity varies by application and oil pan
configuration, ranging from 4.5 liters to 5.5 liters (4.8 US qt to 5.8
US qt). The engine requires diesel engine oil meeting API CD or higher
specification, with viscosity grade selected based on operating ambient
temperatures.
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 suitable for
continuous industrial operation. The water pump is mounted on the front
of the engine block.
The coolant circuit includes a thermostatic bypass that facilitates
rapid warm-up and reduces internal friction during cold starts. The
engine block coolant capacity is 2.4 liters (2.5 US qt) for the engine
block only, with total system capacity depending on radiator size and
application. A cross-flow radiator with an electric or mechanical fan
supplements the system at low engine speeds and during idle conditions.
| Intake and Exhaust Systems |
Air Intake: The intake system incorporates a cast iron intake manifold
designed for durability in industrial 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, though turbocharged (3KR1-T) and turbocharged with
intercooler variants were produced for higher-output applications.
Exhaust System: The exhaust system incorporates a cast iron exhaust
manifold merging into a single exhaust pipe. The system includes a
muffler but may not include catalytic converters, reflecting the
engine’s design for industrial and off-road applications.
Engine Management: The 3KR1 utilizes no electronic engine management
system in its standard mechanical form. Fuel delivery is controlled
mechanically by the injection pump governor. The electrical system
consists of a starter motor, glow plugs for cold-start assistance, and
basic sensors for the instrument cluster.
Glow Plug System: The engine is equipped with glow plugs installed in
the cylinder head to assist with cold starting. The glow plugs are
energized through a glow controller that activates them for a
predetermined duration based on ambient temperature and coolant
temperature.
The dry weight of the 3KR1 engine is 143 kg (315 lb). The engine length,
measured from the front gear cover to the flywheel housing face, is 700
mm (27.6 in). The width, measured at the widest point including the
injection pump and exhaust manifold, is 550 mm (21.7 in). The height,
measured from the oil pan bottom to the top of the cylinder head cover,
is 700 mm (27.6 in). These compact dimensions facilitate installation in
space-constrained equipment such as mini excavators and transport
refrigeration units.
The service life of the 3KR1 under proper operating conditions is
engineered to exceed 10,000 operating hours in industrial applications.
Oil change intervals are recommended at 250 operating hours for severe
service conditions or 500 hours under normal operating conditions. The
engine requires diesel engine oil meeting API CD or higher
specification, with SAE 10W-30, 15W-40, or 20W-50 viscosities selected
based on ambient temperature range.
Valve clearance inspection and adjustment is mandated every 1,000
operating hours. The intake and exhaust valve clearances are both set at
0.40 mm (0.016 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 250-hour intervals.
The coolant must be replaced every 2 years or 2,000 operating hours,
using a nitrite-free, long-life coolant formulation. The accessory drive
belt requires inspection at each service interval, with replacement when
cracking or wear is evident. After servicing, the engine oil pressure
should be verified at 3.0 bar to 5.0 bar (44 psi to 73 psi) at 3,000
rpm.
The cylinder head bolts follow a multi-stage procedure: initial torque
of 35 Nm (25.8 lb-ft), followed by a final torque of 80 Nm (58.9 lb-ft)
in a specified sequence from the center bolts outward in a crisscross
pattern. The connecting rod bolts are torqued to 45 Nm (33.2 lb-ft).
The main bearing cap bolts are torqued to specifications determined by
bolt grade. The oil pan bolts are torqued to 12 Nm (8.9 lb-ft). The
valve cover bolts are torqued to 10 Nm (7.4 lb-ft). The timing belt
tensioner bolt is torqued to 20 Nm (14.8 lb-ft). The water pump bolts
are torqued to 25 Nm (18.4 lb-ft).
The 3KR1 was produced primarily for industrial and commercial
applications rather than passenger vehicles. In the transport
refrigeration sector, the engine is highly common in Thermo King
refrigeration units including the RD-II, TD-II, and SB-II models, where
its ability to run continuously for extended periods is essential for
temperature-controlled cargo transport.
In the construction equipment sector, the 3KR1 powers mini excavators
from major manufacturers including Hitachi (EX series: EX25, EX40 UR
models) and Sumitomo. For the Hitachi EX25, the engine produces 18.4 kW
(25.0 PS / 24.7 hp) at 2,400 rpm with maximum torque of 78.5 Nm (57.9
lb-ft) at 1,800 rpm.
The engine is also used in Sumitomo mini excavators, generators,
welders, and other industrial equipment requiring a compact, durable
diesel power unit for continuous operation. The engine remains in
service across a substantial installed base of equipment, supported
through aftermarket parts channels from suppliers such as Aspect Plus
and Guangzhou Bee Auto Parts Ltd.
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