Isuzu 3AB1 Specifications
| Engine Model: Isuzu 3AB1 |
| Engine Type: 4-stroke in-line 3-cylinder liquid-cooled diesel |
| Total Displacement: 108.4 cu.in (1.77 L) |
| Rated Engine Power: 38 Hp (28 kW) at 2800 rpm |
| Fuel System Type: Indirect injection |
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The Isuzu 3AB1 is a naturally aspirated,
three-cylinder diesel engine belonging to the Isuzu "A" family of
industrial power units. This engine represents a stroked variant within
the family, sharing the 86 mm bore of the 3AA1 but utilizing a longer
102 mm stroke. The increased stroke raises displacement to 1,777 cc,
delivering higher torque output at lower engine speeds compared to its
shorter-stroke counterpart. The 3AB1 shares its 102 mm stroke dimension
with the two-cylinder 2AB1 and the four-cylinder C240 engine, the latter
known as the 4AB1 in many industrial applications.
This family-wide design standardization permitted Isuzu to use common
crankshaft forgings, connecting rods, and piston assemblies across
multiple engine configurations. The engine employs a mechanical Bosch
PES-A type in-line injection pump with an integrated mechanical
governor, rendering it suitable for stationary power applications, small
construction equipment, and agricultural machinery where electronic
controls are not advantageous.
Engine Type: 4-cycle, water-cooled, inline, overhead valve (OHV) diesel
Number of Cylinders: 3
Bore x Stroke: 86 mm x 102 mm (3.39 in x 4.02 in)
Total Displacement: 1,777 cc (108.4 cu.in)
Compression Ratio: 20.0:1
Firing Order: 1-2-3
Rotation (from flywheel end): Counter-clockwise
Power Output: 38 Hp (28 kW) at 2,800 rpm
Peak Torque: 112 Nm (83 lb-ft) at 1,800 rpm
Rated Speed (continuous): 2,400 rpm
Rated Speed (intermittent): 2,800 rpm
Low Idle Speed: 700 to 750 rpm
Aspiration: Naturally aspirated (atmospheric)
Starting System: Electric starter motor (12V)
The cylinder block is manufactured from alloy cast iron using a monobloc
construction. The block is a parent-bore design, meaning cylinder bores
are machined directly into the cast iron without replaceable liners.
Bore surfaces receive a plateau-honed finish to retain oil and support
piston ring sealing. The block features an open-deck design at the top
face, with coolant passages surrounding the upper portion of each
cylinder bore.
Three main bearing bulkheads support the crankshaft, each fitted with
two-bolt caps. The side walls of the block incorporate cast-in ribs to
reduce vibration at the engine's natural frequencies around 2,000 rpm. A
pushrod gallery is cast into the right side of the block, housing the
mechanical fuel injection pump drive gear and the camshaft. The oil pan
mounting rail is reinforced with transverse ribs. The water jacket
extends full depth around each cylinder bore, with larger coolant
passages concentrated between cylinders 2 and 3 where thermal loading is
highest.
The cylinder head is a single-piece cast iron unit with a cross-flow
design. Induction ports are located on the left side of the head when
viewed from the flywheel end, while exhaust ports are on the right side.
The valve train uses a pushrod-actuated, overhead valve (OHV)
configuration with two valves per cylinder: one intake and one exhaust.
Intake valve diameter is 38 mm (1.50 in). Exhaust valve diameter is 32
mm (1.26 in). Both valves are manufactured from silicon-chromium steel
and feature chrome-plated stems.
Embossed rotators are fitted to the exhaust valves to induce rotation
and prevent carbon buildup. The intake valves are not rotated. Valve
lash adjustment is accomplished via set screws and locknuts on the
rocker arm tips. The rocker shaft is a hollow steel tube supported by
three pedestals bolted directly to the cylinder head. The pre-combustion
chamber, a spherical recess known as the swirl chamber, is cast into the
cylinder head above each cylinder. A glow plug is threaded into each
swirl chamber for cold starting assistance.
The fuel system is a mechanical indirect injection system using a Bosch
PES-A type in-line injection pump, identical to units fitted to the
3AA1, C220, and C240 engines. The pump is mounted on the right side of
the cylinder block and driven by a gear from the camshaft. The pump
contains three individual plunger and barrel assemblies, one per
cylinder, actuated by a camshaft within the pump body. A mechanical
governor, integrated into the rear of the injection pump housing,
controls engine speed by regulating fuel rack position.
The governor includes both idle and maximum speed spring sets. Delivery
valves with constant-pressure design prevent secondary injection.
Injection nozzles are of the pintle type, installed in the cylinder head
and positioned to inject fuel into the pre-combustion chamber. Nozzle
opening pressure is set to 11.8 MPa (1,715 psi). A diaphragm-type feed
pump is mounted on the injection pump body and draws fuel from the tank
through a replaceable cartridge-type fuel filter.
The lubrication system is a forced-feed, full-flow pressurized system
using a gear-type oil pump. The oil pump is mounted externally on the
front of the cylinder block and driven directly by the crankshaft gear.
Oil is drawn from a pressed steel oil pan through a mesh suction
strainer positioned 15 mm above the pan floor. The oil filter is a
spin-on, full-flow type with a cellulose media rated for 30-micron
nominal filtration. An integral bypass valve opens at a differential
pressure of 1.2 bar (17 psi) to maintain flow during cold starts or
filter blockage.
The system does not include an oil cooler in the standard configuration,
though a water-cooled oil cooler was an optional extra for high-ambient
or continuous high-load applications. Pistons are cooled by oil splash
from the connecting rod dippers and by oil mist generated within the
crankcase. The engine oil capacity including the filter is 5.8 L (6.1
qt). Operating oil pressure at rated speed of 2,800 rpm is 2.9 to 4.1
bar (42 to 60 psi). Minimum oil pressure at low idle, at operating
temperature, is 0.7 bar (10 psi).
The cooling system is a pressurized, thermosiphon-assisted system with a
belt-driven centrifugal water pump. The water pump uses a ceramic seal
and a pressed steel impeller with six vanes. The thermostat is a
wax-pellet, single-stage design with a rated opening temperature of
76.5°C (170°F) and a fully open position at 90°C (194°F). Coolant flows
from the water pump into the cylinder block, circulates upward around
the cylinder bores, passes into the cylinder head, and exits through the
thermostat housing.
A separate bypass circuit permits coolant circulation during thermostat
closure for uniform warm-up. The system uses a non-pressured recovery
tank on most industrial installations, with a 0.7 bar (10 psi) pressure
cap on the radiator fill neck. The engine-only coolant capacity is 3.7 L
(3.9 qt). A coolant filter is not equipped as standard. A water-cooled
exhaust manifold is not fitted; the dry exhaust manifold is separate.
Timing Drive: A front-mounted gear train drives all engine components.
The crankshaft gear drives an idler gear, which in turn drives the
camshaft gear, injection pump gear, and oil pump drive gear. The
camshaft gear is twice the diameter of the crankshaft gear, providing a
2:1 reduction ratio for 4-cycle operation. All gears are straight-cut
steel for durability.
Crankcase Ventilation: An open crankcase ventilation system routes
blow-by gases through an oil separator made of wire mesh. The separated
oil drains back to the crankcase via a one-way reed valve. Cleaned gases
vent to the atmosphere through a draft tube located on the left side of
the cylinder block.
Electrical System: A 12-volt system is standard, using a 35-amp
alternator and a 1.2 kW starter motor. The alternator is a Hitachi
internally regulated unit. Glow plugs are 6-volt series-type units wired
in series, dropping the system voltage across all three plugs. A glow
plug controller includes a dash-mounted indicator that illuminates for 5
to 10 seconds at 0°C (32°F) before the starter is engaged.
Exhaust System: A dry-type exhaust manifold is cast integrally with the
right side of the cylinder head. The manifold has a single outlet flange
positioned between cylinders 2 and 3. No turbocharger or aftertreatment
devices are fitted.
Dry Weight (without flywheel, starter, alternator, oil, coolant): 217 kg
(478 lb).
Length (from front fan pulley to rear flywheel housing face): 620 mm
(24.4 in).
Width (extreme, including injection pump and exhaust manifold): 470 mm
(18.5 in).
Height (from oil pan rail to rocker cover top): 700 mm (27.6 in).
Engine Oil Capacity (with filter): 5.8 L (6.1 qt).
Recommended Oil Grade: SAE 15W-40 (API CD or CC) or SAE 10W-30.
Coolant Capacity (engine only): 3.7 L (3.9 qt).
Oil Change Interval: 100 operating hours; initial break-in change at 50
hours.
Oil Filter Replacement: 300 operating hours or every third oil change.
Fuel Filter Replacement: 200 operating hours or 6 months.
Intake Valve Clearance (Cold): 0.18 mm (0.007 in).
Exhaust Valve Clearance (Cold): 0.20 mm (0.008 in).
Valve Adjustment Interval: Inspect every 200 hours; adjust as required.
Injection Nozzle Opening Pressure: 11.8 MPa (1,715 psi); reset every 800
hours.
Glow Plug Resistance (each, cold): 0.8 to 1.0 ohm.
Fan Belt Tension (deflection at center span with 10 kg force): 12-15 mm
(0.47-0.59 in).
Cylinder Head Bolts (M12 x 1.5), Stage 1: 50 Nm (37 lb-ft).
Cylinder Head Bolts (M12 x 1.5), Stage 2: 80 Nm (59 lb-ft).
Cylinder Head Bolts (M12 x 1.5), Stage 3: 110 Nm (81 lb-ft).
Cylinder Head Bolts (M12 x 1.5), Stage 4: Final 130 Nm (96 lb-ft).
Connecting Rod Bolts (M9 x 1.0): 50 Nm (37 lb-ft).
Main Bearing Cap Bolts (M12 x 1.5): 100 Nm (74 lb-ft).
Flywheel Bolts (M10 x 1.25): 65 Nm (48 lb-ft).
Flywheel Housing Bolts (M10 x 1.5): 45 Nm (33 lb-ft).
Rocker Shaft Pedestal Nuts (M10): 35 Nm (26 lb-ft).
Rocker Arm Adjusting Locknut: 10 Nm (7 lb-ft).
Injector Nozzle Holder Nuts: 35 Nm (26 lb-ft).
Injection Pump Drive Gear Nut: 80 Nm (59 lb-ft).
Oil Pan Drain Plug (M14 x 1.5): 50 Nm (37 lb-ft).
Industrial: Isuzu C240-powered generator sets repowered with 3AB1; small
compressor units from Ingersoll Rand (models G2 and G3); Daishin
industrial sweepers; Nissan forklift models F02 and F03 (3AB1 variant).
Construction: Mikasa Tamping Rammer series (power unit); Sakai vibration
roller models SV400 and SV500; Yanbaru small excavators (repower
applications).
Agricultural: Isuzu TF series small tractors (select Asian domestic
market models); Kubota-powered implements repowered for parts
availability; stationary irrigation pump drives for rice paddies.
Marine: Small fishing boat auxiliary generators; Yanmar marine gear
repower conversions (30 to 38 hp range).
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