Isuzu 3LD1 Specifications
| Engine Model: Isuzu 3LD1 |
| Engine Type: 4-stroke in-line 3-cylinder liquid-cooled diesel |
| Total Displacement: 91.3 cu.in (1.49 L) |
| Rated Engine Power: 33.3 Hp (24.8 kW) at 3000 rpm |
| Fuel System Type: Indirect injection |
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The Isuzu 3LD1 is a vertical, water-cooled,
3-cylinder diesel engine from Isuzu's L-Series. It features a 1.49-liter
displacement and was primarily used for medium-sized industrial
equipment, mini-excavators such as the Bobcat 331, forklift trucks, and
generator sets. The engine architecture prioritizes compact dimensions
and operational reliability in confined machinery compartments.
Its indirect injection (IDI) combustion system with a swirl chamber
provides smooth operation and reduced combustion noise compared to
direct injection units. Known for a high compression ratio of 22.0:1,
this engine delivers reliable cold-starting performance and efficient
fuel combustion. The overhead valve (OHV) design with pushrods and
rocker arms simplifies maintenance while providing durable service in
demanding environments. A glow plug system (QOS-III) ensures rapid
starting across a wide ambient temperature range.
The Isuzu 3LD1 is a four-cycle, naturally aspirated, inline-three diesel
engine. The cylinder arrangement is vertical, in-line. The bore measures
83.1 mm (3.27 in) and the stroke is 92.0 mm (3.62 in), resulting in a
total displacement of 1,496 cc (91.3 cu.in). The compression ratio is
22.0:1. The firing order is 1-3-2. Rotation is counter-clockwise when
viewed from the flywheel end. The combustion system is indirect
injection (IDI) with a swirl chamber type pre-combustion chamber. Rated
speed varies by application: intermittent power is achieved at 3,000
rpm, while generator applications operate at 1,800 rpm.
Power output for industrial intermittent duty is 24.8 kW (33.3 hp) at
3,000 rpm. Continuous industrial power output is 21.8 kW (29.3 hp) at
3,000 rpm. For generator applications at 1,800 rpm, output is 16.2 kW
(21.7 hp). Maximum torque for industrial intermittent rating is 97 Nm
(71.5 lb-ft) at 1,800 rpm. Continuous torque output is 83.9 Nm (61.9
lb-ft) at 1,800 rpm. The governor is a mechanical centrifugal type
integrated into the injection pump.
The cylinder block is constructed from high-strength cast gray iron with
a deep-skirt design extending below the crankshaft centerline. The
cylinders are integrally cast into the block; no replaceable wet sleeves
are used in this engine family. The parent bore finish is
precision-honed to provide a durable wear surface. The crankcase
incorporates four main bearing supports for the crankshaft, a provision
suitable for the three-cylinder layout.
The main bearing caps are secured with two bolts each. A timing gear
housing is cast integrally at the front of the block, housing the
camshaft drive gear, injection pump drive gear, and balance shaft gears.
The oil pan mounting face is machined flat with a full perimeter rail.
The block incorporates a side-mounted cartridge-type oil filter housing
as an integral casting. The engine is designed for a 30° inclination in
all directions for flexible installation in mobile equipment.
The cylinder head is a single, cast iron unit spanning the entire length
of the three cylinders. The valvetrain uses an overhead valve (OHV)
configuration with pushrods and rocker arms, operating two valves per
cylinder for a total of 6 valves. The camshaft is located in the
cylinder block and driven by a gear train from the crankshaft.
Mechanical flat tappet lifters actuate steel pushrods that transfer
motion to cast rocker arms mounted on a steel shaft. The valves are
arranged in a vertical inline pattern along the cylinder head
centerline.
Intake valve diameter is 32.0 mm (1.26 in); exhaust valve diameter is
28.0 mm (1.10 in). The valve stem seals are positive-type. The
combustion chamber is an indirect injection swirl chamber design, where
a pre-combustion chamber cast into the cylinder head receives the fuel
injector, and the main combustion bowl is machined into the piston
crown. The cylinder head joint uses a composite head gasket with steel
fire rings around each cylinder bore. Mechanical valve lash adjustment
is required; no hydraulic lifters are used.
The fuel system uses an inline mechanical injection pump with a built-in
feed pump. A diaphragm-type transfer pump, mounted on the injection pump
body, draws fuel from the tank through a primary fuel filter with a
water sedimenter. The injection pump is a Bosch-type inline plunger pump
with individual pumping elements for each cylinder. Mechanical governor
and automatic timing advance devices are integrated into the pump
housing. High-pressure injection lines connect the pump to the
pintle-type injectors mounted in the cylinder head's swirl chamber
housings.
The injector opening pressure is 9.8-11.3 MPa (1,420-1,640 psi). A fuel
return line routes excess fuel and injector leakage back to the tank.
The QOS-III glow plug system provides pre-heating for cold starts. Each
cylinder has a glow plug installed in the swirl chamber housing,
controlled by a timer relay that monitors coolant temperature and
post-heats after engine start to reduce white smoke.
The lubrication system is a fully pressurized, wet-sump design with a
trochoid-type oil pump. The pump is driven directly from the crankshaft
nose and located inside the front cover. An oil pick-up tube with a
screen draws oil from the stamped steel oil pan. A cartridge-type,
full-flow oil filter mounts externally on the cylinder block. The filter
incorporates a bypass valve. The main oil gallery runs the full length
of the cylinder block, supplying the four main bearings.
Cross-drilled passages in the crankshaft feed the connecting rod
bearings. A secondary gallery supplies the camshaft bearings and the
rocker arm shaft through external lines. No piston cooling oil jets are
present in this engine. Total oil system capacity, including the filter,
is 6.3 L (6.7 qt / 1.66 gal). Operating oil pressure at rated speed is
2.5-3.5 bar (36-50 psi). The oil pressure relief valve is set at 4.0 bar
(58 psi).
The cooling system is a thermostatically controlled, pressurized liquid
cooling system using a belt-driven centrifugal water pump. The pump is
mounted to the front of the cylinder block and driven by the crankshaft
pulley. Coolant circulates through the block, cylinder head, and
radiator. A wax-pellet thermostat with a rated opening temperature of
71-82°C (160-180°F) is located in a housing on the water pump inlet.
The coolant temperature sensor provides input for the glow plug
controller and the instrument panel gauge. The system uses a coolant
recovery reservoir with a pressure cap rated at 0.5-0.7 bar (7-10 psi).
A 7-blade suction fan with a diameter of 360 mm (12.6 in) provides
forced airflow through the radiator. Engine jacket water capacity
(engine only) is 2.5 L (2.6 qt / 0.66 gal). Total system coolant
capacity including the radiator is 5.0 L (5.3 qt).
| Intake and Exhaust Systems |
Air Intake System: A dry-type air cleaner with a replaceable paper
filter element feeds the intake manifold. The air inlet location is
sideward for flexible installation. A rubber intake hose connects the
air cleaner to the intake manifold.
Exhaust System: A cast iron exhaust manifold collects gases from the
three cylinders and directs them to a single exhaust outlet oriented
front sideward. Exhaust gas temperature at rated load is 450-500°C
(842-932°F). The exhaust outlet flange accepts a flexible pipe
connection to the muffler.
The electrical system operates at 12 volts DC with negative grounding.
The charging system uses a belt-driven AC alternator rated at 12V-20A,
with an integral voltage regulator. The starting system includes a
reduction-gear starter motor rated at 12V-1.2 kW. The QOS-III glow plug
system operates on a timer relay that provides pre-heat for 3-6 seconds
depending on coolant temperature, followed by post-heat for up to 30
seconds after start.
Overall length is 585.5 mm (23.0 in) from the fan to the flywheel
housing mounting face. Width across the cylinder block, including the
injection pump and oil filter, is 475 mm (18.7 in). Height from the oil
pan rail to the top of the rocker arm cover is 609 mm (24.0 in). The dry
weight of the fully dressed engine, including flywheel, alternator,
starter, and exhaust manifold but without fluids, is 132 kg (291 lb).
The center of gravity is located 300 mm (11.8 in) from the flywheel
housing face and 220 mm (8.7 in) above the crankshaft centerline.
Engine Oil: The oil and filter change interval is 250 hours under normal
operating conditions using API CF or higher rated diesel oil. Oil grade
is SAE 15W-40 for ambient temperatures above -10°C (14°F), or SAE 10W-30
for cold climates. System volume is 6.3 L (6.7 qt). Fuel Filters: The
primary fuel filter/water separator element is replaced every 250 hours
or 12 months. The secondary fuel filter is replaced concurrently.
Air Cleaner: The air filter element requires inspection every 50 hours
and replacement when the restriction indicator shows a vacuum of 6.2
kPa. More frequent service is required in dusty environments. Cooling
System: Coolant replacement interval is 1,000 hours or 24 months. Use a
low-silicate ethylene glycol coolant with anti-corrosion additives at a
30-50 percent concentration.
Valve Clearance: Inspection and adjustment are required every 500 hours.
Cold valve clearances are: intake 0.20 ± 0.05 mm (0.008 ± 0.002 in),
exhaust 0.20 ± 0.05 mm (0.008 ± 0.002 in). Both intake and exhaust
valves use the same clearance specification. Adjustment is performed
with the engine cold, using a feeler gauge between the rocker arm and
valve stem end.
Compression Pressure: Standard compression pressure is 3.04 MPa (441
psi) at 250 rpm. The minimum service limit is 2.55 MPa (370 psi).
Maximum variation between cylinders is 0.3 MPa (44 psi). Injector
Replacement: Injectors are inspected every 1,000 hours and replaced as
necessary. The injection pump requires professional calibration. Glow
Plugs: Glow plug resistance is checked every 500 hours. Resistance at
20°C should be 0.8-1.0 ohms per plug.
Cylinder Head Bolts: Stage 1: 74-83 Nm (54-61 lb-ft).
Connecting Rod Nuts: 25-34 Nm (18-25 lb-ft).
Main Bearing Cap Bolts: 19-28 Nm (14-21 lb-ft).
Flywheel Bolts: 19-28 Nm (14-21 lb-ft).
Rocker Arm Shaft Brackets: 19-28 Nm (14-21 lb-ft).
Rocker Arm Adjusting Lock Nuts: 15-20 Nm (11-15 lb-ft).
Intake and Exhaust Manifold Nuts: 15-20 Nm (11-15 lb-ft).
Valve Cover Bolts: 8-12 Nm (6-9 lb-ft).
Oil Pan Bolts: 8-12 Nm (6-9 lb-ft).
Injection Pipe Nuts: 19-28 Nm (14-21 lb-ft).
Glow Plugs: 15-20 Nm (11-15 lb-ft).
The Isuzu 3LD1 engine was utilized across a range of compact industrial
and construction equipment from approximately 1988 through 2005.
Construction Equipment:
Bobcat 331 and X331 Mini-Excavators: The primary application for this
engine, providing reliable power for digging and lifting operations.
Bobcat 325 and 328 Mini-Excavators: Some variants using the 3LD1 power
unit.
Material Handling:
Forklift trucks: Various manufacturers using the 3LD1 for compact
counterbalance forklifts in the 1.5-2.5 ton capacity range.
Power Generation:
Compact diesel generators: Standby and prime power generator sets rated
at 16 kW (continuous) to 20 kW (standby).
Light towers and portable power units.
Industrial Equipment:
Concrete pumps: Small trailer-mounted concrete pumping units.
Agricultural sprayers and compact tractors: Specialized orchard and
vineyard tractors requiring compact power.
Welding generators and air compressors: Portable industrial equipment
packages.
Irrigation pumps: Stationary engine-driven pump sets for agricultural
water transfer.
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