Isuzu 4ZA1 Specifications
| Engine Model: Isuzu 4ZA1 |
| Engine Type: 4-stroke in-line 4-cylinder liquid-cooled gasoline |
| Total Displacement: 96.6 cu.in (1.58 L) |
| Rated Engine Power: 73-80 Hp (55-60 kW) at 5400 rpm |
| Fuel System Type: Downdraft carburetor |
____________________________________________________________________________________
The Isuzu 4ZA1 is a 1.6-liter, water-cooled,
in-line 4-cylinder gasoline engine from the Isuzu Z-series family.
Produced throughout the 1980s, this engine represents a transition from
older pushrod designs to a modern overhead camshaft (SOHC)
configuration. Unlike Isuzu’s famous diesel engines, the 4ZA1 is a
petrol powerplant designed for light commercial vehicles, utility
trucks, and early sport utility vehicles. It was extensively used in the
Isuzu Faster (also known as the KB or PUP) and the first-generation
Isuzu Trooper (sold as the Holden Jackaroo in Australia).
The 4ZA1 is an undersquare engine with a bore of 82.0 mm (3.23 in) and a
stroke of 75.0 mm (2.95 in), favoring responsiveness over low-end
lugging torque. Its architecture includes a cast iron cylinder block and
an aluminum alloy cylinder head. The single overhead camshaft is driven
by a rubber timing belt, a maintenance item requiring periodic
replacement.
The engine features an 8-valve layout (two valves per cylinder) with a
simple carbureted fuel system, usually a Nikki twin-barrel downdraft
unit. While not a high-performance engine by modern standards, the 4ZA1
is valued for its mechanical simplicity, reliability, and ease of
service. It served as the smaller-displacement sibling to the 1.8 L 4ZB1
and the 2.3 L 4ZD1, sharing many design principles and some
interchangeable components across the Z-series.
The Isuzu 4ZA1 is a 4-stroke, spark-ignition, in-line 4-cylinder
gasoline engine. The engine is naturally aspirated without any
supercharging or turbocharging systems. Total displacement is 1,584 cc
(96.6 cu.in). The bore and stroke dimensions are 82.0 mm x 75.0 mm (3.23
in x 2.95 in). This short-stroke configuration relative to bore creates
a square-to-oversquare design, permitting higher engine speeds. The
compression ratio is 8.5:1, suited for regular-grade gasoline of 87-91
octane. The firing order is 1-3-4-2, a standard layout for in-line
4-cylinder engines that balances primary and secondary forces. Engine
rotation, when viewed from the flywheel end, is clockwise.
Maximum Power (SAE gross): 55-60 kW (73-80 hp) @ 5,400 rpm
Maximum Torque: 123 Nm (91 lb-ft) @ 3,000 rpm
Rated Engine Speed (maximum continuous): 5,400 rpm
Low Idle Speed: 800 rpm
High Idle Speed (no load, governed): 6,000 rpm
Governor Type: None (fuel cutoff via manual throttle)
The cylinder block is a one-piece, cast iron design with a deep-skirt
configuration extending below the crankshaft centerline. This
construction provides a rigid foundation for the rotating assembly and
reduces vibration at idle. The block features 5 main bearing supports,
each cap secured by two bolts. The cylinders are integral to the block
(parent bore design) without replaceable cylinder liners. The bore
surfaces are chromium-plated or hardened by induction treatment for wear
resistance.
The crankshaft is cast from nodular iron, with induction-hardened
journal surfaces. The crankshaft is supported by five main bearings,
with thrust washers located at the center bearing (number 3) to control
axial play. Connecting rods are forged steel, machined as matched sets
with the cap. The pistons are cast aluminum alloy with a tin-plated or
molybdenum-coated skirt. Each piston carries three rings: two
compression rings (upper and intermediate) and one oil control ring. The
piston pin is a full-floating type retained by circlips.
Number of Main Bearings: 5
Main Bearing Journal Diameter: 55.0 mm (2.17 in)
Connecting Rod Length (center-to-center): 131.0 mm (5.16 in)
Connecting Rod Big End Bore: 49.0 mm (1.93 in)
Piston Pin Diameter: 20.0 mm (0.79 in)
Piston Ring Width (top compression): 1.5 mm (0.059 in)
The cylinder head is a cross-flow, aluminum alloy casting spanning all 4
cylinders. The cross-flow design positions the intake manifold on one
side of the head and the exhaust manifold on the opposite side,
improving volumetric efficiency by keeping the intake charge cool. The
valvetrain utilizes a single overhead camshaft (SOHC) running directly
in aluminum bearings machined into the head. The camshaft is driven by a
rubber timing belt from the crankshaft sprocket. The camshaft acts
directly on mechanical bucket tappets (lash adjusters). Each tappet is a
cylindrical shim sitting between the cam lobe and the valve stem.
Each cylinder has two valves: one intake and one exhaust (8 valves
total). The valves are arranged in a parallel configuration, with the
intake valves angled at 20 degrees from the vertical and exhaust valves
at 20 degrees on the opposite side. The combustion chamber is a
hemispherical or pentroof design, promoting flame propagation across the
piston crown. The valve seats are pressed-in alloy steel inserts for
both intake and exhaust. Valve guides are sintered iron, replaceable via
service tools. Valve lash adjustment is mechanical, requiring the
replacement of the shim (selective fitting) on top of each tappet.
Valve Arrangement: Overhead camshaft (SOHC), cross-flow, 2 valves per
cylinder
Intake Valve Diameter: 38.0 mm (1.50 in)
Exhaust Valve Diameter: 32.0 mm (1.26 in)
Valve Lift (intake and exhaust): 9.0 mm (0.354 in)
Valve Lash (hot, intake): 0.20 mm (0.008 in)
Valve Lash (hot, exhaust): 0.25 mm (0.010 in)
Timing Belt Replacement Interval: 80,000 km (50,000 miles) or 5 years
The fuel system uses a downdraft carburetor mounted on top of the intake
manifold. The carburetor is a Nikki 2-barrel (twin-choke) unit with
progressive linkage. The primary barrel handles idle and light-load
operation, while the secondary barrel opens under heavy throttle for
additional airflow and fuel delivery. The carburetor incorporates an
automatic choke (bi-metallic coil type) for cold starts, a fast idle
cam, and an accelerator pump for transient enrichment. A mechanical fuel
pump, mounted on the cylinder block and actuated by an eccentric on the
camshaft, draws fuel from the tank and delivers it to the carburetor at
0.2-0.3 bar (3-4 psi).
The intake manifold is a two-piece aluminum casting with a water-heated
passage (coolant crossover) to warm the intake charge during cold
weather, preventing carburetor icing. An air cleaner housing (full-flow,
dry paper element) mounts directly above the carburetor.
Carburetor Type: Nikki 2-barrel downdraft or Hitachi equivalent
Primary Barrel Diameter: 28.0 mm (1.10 in)
Secondary Barrel Diameter: 32.0 mm (1.26 in)
Fuel Pump Type: Mechanical diaphragm, camshaft-actuated
Fuel Pump Pressure: 0.2-0.3 bar (3-4 psi)
Fuel Grade: Regular unleaded, 87 octane (R+M/2)
Idle Fuel Mixture Adjustment: Adjustable screw on carburetor body
The lubrication system is a full-pressure, forced-feed design using a
gear-type oil pump. The oil pump is mounted inside the oil pan, driven
by the crankshaft via a distributor shaft or a dedicated gear. Oil is
drawn from the sump through a wire mesh strainer, pressurized by the
pump, and then routed through a full-flow oil filter (spin-on, cellulose
media). A bypass valve opens at 1.5 bar (22 psi) differential pressure
to maintain oil flow if the filter becomes restricted. After filtration,
oil is distributed to the main bearings, connecting rod bearings,
camshaft bearings, and cylinder head.
The oil pan is a stamped steel sump. A crankcase ventilation system (PCV
- Positive Crankcase Ventilation) routes blow-by gases from the
crankcase back into the intake manifold to be burned. The PCV valve is a
one-way flow control device mounted on the valve cover.
Oil Capacity (with filter, standard sump): 3.8 L (4.0 U.S. qt)
Oil Capacity (deep sump, some utility vehicles): 4.2 L (4.4 U.S. qt)
Oil Pressure (rated speed, 3,000 rpm): 275-400 kPa (40-58 psi)
Oil Pressure (low idle, 800 rpm, hot): 70 kPa (10 psi) minimum
Recommended Oil Viscosity: SAE 10W-30 or 10W-40 (API SF, SG, or SH
rating)
Oil Change Interval (normal duty): 5,000 km (3,000 miles) or 6 months
Oil Pan Type: Stamped steel
The cooling system is a pressurized, liquid-cooled design with a
centrifugal water pump. The water pump is belt-driven from the
crankshaft pulley and uses a sealed ball bearing and a carbon-ceramic
face seal. Coolant flows from the lower radiator tank into the pump,
then through the cylinder block water jackets, upward through the
cylinder head, and out through the thermostat housing. A separate bypass
circuit routes coolant around the block until the thermostat opens.
The system incorporates a wax-pellet thermostat located in a housing at
the front of the cylinder head. The thermostat begins opening at 82°C
(180°F) and is fully open at 95°C (203°F). The radiator is a cross-flow
or vertical-flow design, manufactured from copper-brass or aluminum with
plastic tanks depending on the vehicle application. An electric cooling
fan or engine-driven fan (viscous or direct clutch) moves air across the
radiator.
Coolant Capacity (engine only, no radiator): 2.5 L (2.6 U.S. qt)
Coolant Capacity (engine with standard radiator): 7.5 L (7.9 U.S. qt)
Thermostat Opening Temperature: 82°C (180°F)
Thermostat Fully Open Temperature: 95°C (203°F)
Radiator Cap Pressure: 90-110 kPa (13-16 psi)
Water Pump Type: Centrifugal, belt-driven
Coolant Type: Ethylene glycol antifreeze (green) mixed 50/50 with
distilled water
The exhaust manifold is a cast iron, single-outlet design. The manifold
routes gases to a single exhaust pipe, then through a catalytic
converter on vehicles sold in markets with emissions regulations. A
single muffler and a tailpipe complete the system. An oxygen sensor
(lambda sensor) is present on electronically controlled carburetor or
later fuel-injected variants, but early 4ZA1 engines have no closed-loop
fuel control.
| Ignition and Electrical System |
Ignition System: The ignition system is a conventional breaker-point or
electronic distributor design, depending on production year. Early
models (pre-1985) use a distributor with mechanical breaker points, a
condenser, and a centrifugal and vacuum advance mechanism. Later models
use a fully electronic ignition with a magnetic pickup (reluctor) inside
the distributor and an external ignition control module. The ignition
coil is a conventional oil-filled canister type. Spark plug wires are
carbon-core suppression type to reduce radio interference.
Ignition Timing (base, vacuum disconnected): 6° BTDC @ 800 rpm.
Ignition Timing (full mechanical advance): 28-32° BTDC @ 4,000 rpm.
Dwell Angle (breaker point models): 49-55 degrees.
Spark Plug Type: NGK BP6ES or BPR6ES (resistor type); equivalent Denso
W20EP-U.
Spark Plug Gap: 0.8-0.9 mm (0.031-0.035 in).
Electrical System: The electrical system is 12-volt with negative
ground. The starter motor is a pre-engaged type with an integral
solenoid. The alternator is a 12-volt, internally regulated unit with an
output of 40-60 A depending on vehicle specification. The battery is a
lead-acid, maintenance-free or low-maintenance type with a capacity of
45-60 Ah.
Overall Length (front of water pump to flywheel face): 560 mm (22.0 in)
Overall Width (valve cover edge to oil pan edge): 510 mm (20.1 in)
Overall Height (bottom of oil pan to top of cam cover): 650 mm (25.6 in)
Dry Weight (complete engine, no fluids): 125 kg (276 lb)
Weight (long block with flywheel): 100 kg (220 lb)
Valve Lash (hot, intake, engine at operating temperature): 0.20 mm
(0.008 in).
Valve Lash (hot, exhaust, engine at operating temperature): 0.25 mm
(0.010 in).
Valve Lash Adjustment Interval: 30,000 km (18,600 miles) or 24 months.
Valve Lash Adjustment Method: Shim replacement (mechanical tappets).
Engine Oil Change Interval: 5,000 km (3,000 miles) or 6 months.
Oil Filter Change Interval: Every oil change (5,000 km / 3,000 miles).
Timing Belt Replacement Interval: 80,000 km (50,000 miles) or 5 years.
Spark Plug Replacement Interval: 20,000 km (12,500 miles) for copper
plugs.
Spark Plug Replacement Interval: 60,000 km (37,000 miles) for platinum
plugs.
Coolant Change Interval: 40,000 km (25,000 miles) or 2 years.
Air Cleaner Element Replacement: 20,000 km (12,500 miles).
Fuel Filter Replacement Interval: 40,000 km (25,000 miles).
Ignition Timing Check Interval: 20,000 km (12,500 miles).
Carburetor Idle Speed Check Interval: 10,000 km (6,200 miles).
PCV Valve Replacement Interval: 50,000 km (31,000 miles).
Cylinder Head Bolts (M11 x 1.5), Step 1: 30 Nm (22 lb-ft)
Cylinder Head Bolts (M11 x 1.5), Step 2: 60 Nm (44 lb-ft)
Cylinder Head Bolts (M11 x 1.5), Step 3: 90 Nm (66 lb-ft)
Main Bearing Cap Bolts (M12 x 1.5), Step 1: 30 Nm (22 lb-ft)
Main Bearing Cap Bolts (M12 x 1.5), Step 2: 65 Nm (48 lb-ft)
Connecting Rod Cap Bolts (M9 x 1.0): 42 Nm (31 lb-ft)
Flywheel Bolts (M10 x 1.25): 70 Nm (52 lb-ft)
Camshaft Bearing Cap Bolts (M6 x 1.0): 12 Nm (9 lb-ft)
Camshaft Timing Belt Sprocket Bolt (M12 x 1.25): 80 Nm (59 lb-ft)
Intake Manifold Nuts/Bolts (M8 x 1.25): 18 Nm (13 lb-ft)
Exhaust Manifold Nuts (M8 x 1.25): 18 Nm (13 lb-ft)
Rocker Cover Bolts (M6 x 1.0): 7 Nm (5 lb-ft)
Oil Pan Bolts (M6 x 1.0): 10 Nm (7 lb-ft)
Water Pump Bolts (M8 x 1.25): 18 Nm (13 lb-ft)
Thermostat Housing Bolts (M8 x 1.25): 18 Nm (13 lb-ft)
Spark Plugs: 25 Nm (18 lb-ft)
Oil Filter (spin-on): 15 Nm (11 lb-ft)
Starter Motor Bolts (M10 x 1.25): 40 Nm (30 lb-ft)
Alternator Bracket Bolts (M8 x 1.25): 18 Nm (13 lb-ft)
Crankshaft Pulley Bolt (M14 x 1.5): 170 Nm (125 lb-ft)
Camshaft Timing Belt Tensioner Bolt (M8 x 1.25): 30 Nm (22 lb-ft)
The Isuzu 4ZA1 engine was utilized in light commercial and utility
vehicles throughout the 1980s and early 1990s.
Isuzu Faster / KB / PUP (KB21, KB26, KB40 series): The primary
application. This light pickup truck was sold globally under multiple
names: Isuzu Faster (Japan, Southeast Asia), Isuzu KB (South Africa,
Australia), Isuzu PUP (North America), and Chevrolet LUV (rebadged). The
4ZA1 was the base gasoline engine in many markets.
Isuzu Trooper I (first generation, 1983-1991): Sold as the Isuzu Trooper
in North America and Japan, and as the Holden Jackaroo in Australia. The
4ZA1 was the entry-level gasoline engine in certain markets, usually
paired with a 4-speed or 5-speed manual transmission.
Isuzu WFR / Fargo: A light commercial van and shuttle bus produced by
Isuzu. The 4ZA1 provided power for passenger and cargo variants in Asian
and Australian markets.
Isuzu MU (first generation): A short-wheelbase, two-door SUV derived
from the Faster pickup. The 4ZA1 appeared in early models as a gasoline
option.
Holden Rodeo (first generation, 1981-1988): The Australian-market
version of the Isuzu Faster. The 4ZA1 was fitted as the standard
gasoline engine in the Rodeo utility vehicle before the introduction of
the 1.8 L and 2.0 L engines.
____________________________________________________________________________________
| Industrial Engines Technical Specifications |
| Car Engines Technical Specifications |
| Small Engines Technical Specifications |
| Outboard Engines Technical Specifications |
