Isuzu 3LD2 Specifications
| Engine Model: Isuzu 3LD2 |
| Engine Type: 4-stroke in-line 3-cylinder liquid-cooled diesel |
| Total Displacement: 91.3 cu.in (1.49 L) |
| Rated Engine Power: 37.5 Hp (27.5 kW) at 3000 rpm |
| Fuel System Type: Indirect injection |
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The Isuzu 3LD2 is a 1.5-liter, naturally
aspirated, three-cylinder diesel engine manufactured by Isuzu Motors.
This powerplant belongs to the Isuzu L-Series engine family, a platform
engineered for compact construction equipment, small agricultural
machinery, and generator sets. The 3LD2 has gained recognition for its
quiet operation, low exhaust emissions, and reliable cold starting
performance, characteristics achieved through indirect injection
combustion and a rigid engine structure.
The engine operates on a four-stroke, compression-ignition cycle with an
overhead valve (OHV) configuration and a swirl-type precombustion
chamber for each cylinder. This indirect injection system reduces
combustion noise and nitrogen oxide emissions compared to direct
injection designs, a valuable trait for equipment operating in
noise-sensitive urban environments or indoor applications such as aerial
lifts inside warehouses.
Isuzu engineered the 3LD2 with a gear-driven camshaft, a water-cooled
cylinder block, and a 12-volt glow plug system for cold weather
starting. The engine carries U.S. EPA Tier 2 and European Stage II
emissions certification in its standard configuration, demonstrating
Isuzu’s early commitment to off-road diesel emissions reduction.
The 3LD2 is installed in equipment from multiple original equipment
manufacturers (OEMs), including Hitachi EX35 and EX40 mini excavators,
Case compact excavators, JCB mini excavators, John Deere compact
tractors, and Denyo generators, where it delivers dependable service at
a rated power of 32.5 horsepower at 3,000 rpm. A turbocharged variant,
designated 3LD2T, exists for applications requiring higher power output.
The Isuzu 3LD2 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 1,496 cc, equivalent to 91.3 cubic inches. The
bore dimension is 83.1 mm (3.27 in), and the stroke dimension is 92.0 mm
(3.62 in). The compression ratio is fixed at 21.5:1, a value appropriate
for indirect injection combustion.
The firing order sequence is 1-3-2, a configuration that provides
acceptable balance for a three-cylinder engine with a 120-degree
crankshaft throw interval. Maximum power output reaches 27.5 kW,
equivalent to 37.5 horsepower, at an engine speed of 3,000 rpm. Peak
torque is 94 Nm, equivalent to 69 lb-ft, at an engine speed of 2,000
rpm. Low idle speed is set to 1,000 rpm. The combustion system is
indirect injection, utilizing a swirl-type precombustion chamber for
each cylinder.
The cylinder block is constructed from cast iron, providing rigidity,
vibration damping, and wear resistance required for long service in
construction equipment environments. The block is an inline
three-cylinder design with integral cylinder bores; this engine does not
use replaceable cylinder liners or sleeves. The bores are machined
directly into the cast iron block.
A four-main-bearing crankshaft support structure is employed, meaning
the crankshaft rotates on four bearing journals. This configuration,
with three connecting rod journals positioned between four main
bearings, provides adequate support for the 3,000 rpm rated speed and
torque output of 94 Nm. The block skirt extends below the crankshaft
centerline, contributing to structural rigidity.
The water jacket surrounds the entirety of the cylinder bores to
maximize heat transfer away from the combustion zone. Specific
engineering attention was given to the gear train housing area, where
the rigidity of the block was optimized to minimize gear train noise and
vibration, directly contributing to the engine’s reputation for quiet
operation. The cylinder block includes mounting provisions for the
injection pump on the side of the engine and for the starter motor on
the flywheel housing flange.
The cylinder head is a separate cast-iron component bolted to the top of
the cylinder block using a single-piece head gasket. The head houses the
overhead valve (OHV) mechanism and the precombustion chamber inserts.
Each of the three cylinders has a spherical or swirl-type precombustion
chamber cast into the cylinder head. A glow plug is installed in each
precombustion chamber to assist cold starting.
The valvetrain is actuated by a camshaft located within the cylinder
block, driven by a gear train at the front of the engine. Camshaft lobes
contact mechanical flat-faced lifters (tappets), which push hollow
pushrods upward. The pushrods transmit motion to rocker arms mounted on
a single shaft. The rocker arms pivot to open the valves against spring
pressure. 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 (the
precombustion chamber) and partly in the piston crown, which contains a
swirl-inducing recess. Valve lash is adjustable via set screws on the
rocker arms. Cold valve clearance specification for both intake and
exhaust valves is 0.40 mm (0.0157 in). Valve seat angles are 45 degrees.
The cylinder head gasket is a metal-and-asbestos composite or a
multi-layer steel (MLS) design, depending on the production year.
The fuel system employs an indirect injection design with a mechanical
distributor-type injection pump. The injection pump is a Bosch PFR
series pump or an equivalent licensed design. 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 speed control (1,000 rpm) and
high-speed limiting control. 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 distributes it to individual injection lines. These steel lines
carry high-pressure fuel to the injection nozzles mounted in the
cylinder head. Each injection nozzle is a multi-hole, pintle-type design
with a spring-loaded needle valve.
The nozzle sprays fuel into the precombustion chamber, where initial
combustion begins. The burning gases then expand through a nozzle
orifice into the main combustion chamber in the cylinder. This two-stage
combustion process reduces peak cylinder temperatures and pressures,
lowering NOx emissions and combustion noise. The injector opening
pressure is factory set between 11.8 MPa and 12.7 MPa (1,710 psi and
1,840 psi). 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
trochoid-type oil pump. The oil pump is driven directly by a gear on the
crankshaft and is located inside the oil pan or on the front timing
cover, 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 four 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, including the
camshaft lobes, lifters, pushrod ends, rocker arms, and valve stems.
The system capacity, including the oil filter, is 5.1 liters, equivalent
to 5.4 US quarts. Operating oil pressure at rated engine speed (3,000
rpm) should register between 250 kPa and 400 kPa (36 psi and 58 psi). A
pressure relief valve, located near the oil pump outlet, opens to
prevent excessive pressure during cold starts.
The cooling system is a pressurized, pump-circulated water system
designed for compact equipment packaging. 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 thermostat
is located in a housing at the front or side of the cylinder head. 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 2.4 liters, equivalent to 2.5 US quarts. A fan
attached to the water pump pulley draws air through the radiator core.
For compact construction equipment applications, the radiator is sized
for an ambient temperature capability of up to 40°C (104°F). A coolant
recovery tank is connected to the radiator overflow tube on most
installations.
| Intake and Exhaust Systems |
Air Intake System: Air enters through a dry-type, two-stage air cleaner
fitted with a primary filter element and a safety element. The intake
manifold distributes air evenly to all three cylinders. The intake
manifold is a cast-iron or aluminum component mounted to the cylinder
head.
Exhaust System: Exhaust gases exit each cylinder through the exhaust
manifold, which collects gases into a single pipe. An exhaust muffler
reduces noise emissions.
The electrical system is 12-volt with negative ground. A gear-reduction
starter motor engages with the flywheel ring gear. A belt-driven
alternator, rated between 35 amperes and 60 amperes, charges the
battery. A glow plug system provides cold starting assistance.
Each of the three glow plugs is installed in the cylinder head, directly
accessing the precombustion chamber. Glow plug operating voltage is 12
volts, with a preheat time of 5 to 10 seconds depending on ambient
temperature. A glow plug indicator lamp on the equipment dashboard
signals the operator when the preheat cycle is complete.
The complete engine assembly, including the injection pump, manifolds,
alternator, starter, and flywheel housing, has an overall length of 600
mm (23.6 in), a width of 450 mm (17.7 in), and a height of 650 mm (25.6
in). The dry weight, excluding fluids but including all standard
engine-mounted accessories, is 145 kg (320 lb).
Engine oil and filter should be changed every 250 hours under normal
conditions and every 150 hours under severe duty (heavy dust, high
ambient temperature above 35°C / 95°F, or frequent load cycling). Oil
viscosity selection follows API service classification CF or higher.
Recommended viscosities are SAE 15W-40 for year-round use in
temperatures above -10°C (14°F) and SAE 10W-30 for winter operation
below -10°C.
The fuel filter (primary water separator and secondary spin-on filter)
requires replacement every 500 hours. The air cleaner primary element
requires cleaning every 100 hours in dusty environments and replacement
every 500 hours. The safety element requires replacement every 1,000
hours. Valve lash adjustment is required every 500 hours. The cooling
system requires draining, flushing, and refilling with a fresh mixture
of ethylene glycol antifreeze and distilled water (50/50 ratio) every
1,000 hours or one year.
The thermostat replacement interval is 1,000 hours. The water pump
bearing requires no maintenance, being a sealed unit. The injection pump
timing should be checked every 1,500 hours. The fuel injectors require
testing and recalibration every 1,500 hours. Glow plug resistance should
be checked every 500 hours; a glow plug with infinite resistance (open
circuit) requires replacement.
Cylinder head bolts are tightened in a three-step sequence. First pass
torque is 30 Nm (22 lb-ft). Second pass torque is 60 Nm (44 lb-ft).
Final pass torque is 85 Nm (63 lb-ft). Connecting rod cap bolts are
torqued to 45 Nm (33 lb-ft). Main bearing cap bolts receive 70 Nm (52
lb-ft). Flywheel bolts are tightened to 80 Nm (59 lb-ft). The crankshaft
front pulley bolt is torqued to 120 Nm (89 lb-ft).
The camshaft thrust plate bolts receive 20 Nm (15 lb-ft). 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 Isuzu 3LD2 engine powers a wide range of compact construction,
agricultural, and industrial equipment. Primary applications include
mini hydraulic excavators. Hitachi EX35 and EX40 mini excavators use the
3LD2 as their standard power unit. Case compact excavators in the 35 to
40 metric ton class utilize this engine. JCB mini excavators, including
the 8035 and 8040 models, are equipped with the 3LD2.
Agricultural applications include John Deere compact tractors in the 20
to 30 horsepower range, such as the John Deere 750, 770, and 790 models.
Aerial lift applications include self-propelled boom lifts and scissor
lifts from manufacturers including JLG, Genie, and Skyjack. Generator
applications include Denyo portable generator sets producing 7 kVA to 15
kVA of electrical power. Industrial applications include small wood
chippers, concrete mixers, and hydraulic power packs.
The 3LD2 is distinct from the smaller Isuzu 2LD2 (two-cylinder,
1.0-liter) and the larger Isuzu 4LD2 (four-cylinder, 2.0-liter) engines,
which share the same 83.1 mm bore and 92.0 mm stroke dimensions but
differ in cylinder count. A turbocharged variant, designated Isuzu
3LD2T, exists for applications requiring up to 45 horsepower; this
variant uses the same cylinder block and crankshaft but adds a
turbocharger and modified injection pump calibration.
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