Isuzu G161 Specifications
| Engine Model: Isuzu G161 |
| Engine Type: 4-stroke in-line 4-cylinder 8-valve SOHC liquid-cooled gasoline |
| Total Displacement: 96.6 cu.in (1.58 L) |
| Rated Engine Power: 67-75 Hp (50-56 kW) at 5400 rpm |
| Fuel System Type: Carburetor |
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The Isuzu G161 engine, including the G161Z
high-performance version, is a 1.6-liter, four-cylinder gasoline engine.
Produced from the early 1970s through the mid-1980s, this powerplant
powered numerous Isuzu vehicles, including the Isuzu Gemini (Bellett),
Chevrolet LUV, and early Isuzu Pickups (KB series). The G161 represented
Isuzu's engineering approach to compact, durable powerplants for the
growing small truck and economy car markets.
The G161Z variant incorporated refinements for improved emissions
compliance and marginally higher output, reflecting the evolving
regulatory environment of the late 1970s. The engine's architecture,
featuring a cast-iron block with an aluminum cross-flow cylinder head
and timing chain-driven camshaft, prioritized reliability and
serviceability over peak power output.
The G161 engine is recognized for its robust construction,
straightforward maintenance, and long service life. The use of a timing
chain instead of a belt eliminates scheduled replacement intervals,
reducing long-term ownership costs. The cast-iron cylinder block
provides durability for sustained operation, while the aluminum
cross-flow cylinder head improves thermal management and volumetric
efficiency. The SOHC valvetrain with two valves per cylinder offers a
balance between performance and mechanical simplicity.
The Hitachi twin-barrel carburetor delivers reliable fuel metering
across the engine speed range, though periodic adjustment is required
for optimal performance. The G161Z variant, with its higher compression
ratio and revised camshaft profile, delivers improved driveability in
emissions-controlled applications. The engine remains popular among
vintage Isuzu enthusiasts due to parts availability and straightforward
rebuild procedures.
Engine Type: Inline 4-cylinder, 4-cycle, water-cooled SOHC gasoline.
Displacement: 1,584 cc (96.6 cu.in), equivalent to 1.6 L.
Bore: 82.0 mm (3.23 in).
Stroke: 75.0 mm (2.95 in).
Compression Ratio (Standard G161): 8.7:1.
Compression Ratio (G161Z Variant): 9.0:1.
Firing Order: 1-3-4-2.
Valvetrain: SOHC, 8 valves (2 valves per cylinder).
Camshaft Drive: Timing chain (single row).
Maximum Power: 50-56 kW (67-75 hp) @ 5,000-5,400 rpm.
Maximum Torque: 110-118 Nm (81-87 lb-ft) @ 3,400-3,800 rpm.
Idle Speed: 800 rpm.
The cylinder block is constructed from cast iron, providing the
durability and structural rigidity required for long-term reliability.
The closed-deck design incorporates cast-iron cylinder bores machined
directly into the block without separate liners. The block features a
deep-skirt configuration extending below the crankshaft centerline, with
reinforced bulkheads at each of the five main bearing locations.
The five-main-bearing crankshaft is supported by steel-backed,
lead-indium plated bearing shells. The block incorporates integrated oil
galleries supplying the crankshaft main bearings, connecting rod
bearings, and camshaft bearings. A side-mounted mechanical fuel pump is
mounted to the block and actuated by an eccentric lobe on the camshaft.
The engine mounts are cast into the block sides for direct chassis
attachment.
The cylinder head is manufactured from aluminum alloy and features a
cross-flow design, with intake ports on one side and exhaust ports on
the opposite side. This configuration improves volumetric efficiency and
reduces exhaust valve temperatures. The SOHC arrangement operates two
valves per cylinder through rocker arms. Intake valves measure 40.0 mm
(1.57 in) in diameter, while exhaust valves measure 35.0 mm (1.38 in).
The combustion chambers feature a hemispherical or wedge design
depending on the production year. Valve clearance is adjusted by a screw
and locknut on each rocker arm, requiring periodic inspection. The
camshaft is supported by four bearing journals machined directly into
the cylinder head casting with removable bearing caps. The aluminum head
contributes to reduced overall engine weight compared to all-cast-iron
designs of the era.
The fuel system employs a carburetor architecture utilizing a Hitachi
twin-barrel downdraft carburetor on most variants. The carburetor
incorporates a primary throttle plate for normal operation and a
secondary throttle plate that opens under high load conditions,
providing increased airflow and fuel delivery. A mechanical fuel pump,
mounted on the cylinder block and actuated by the camshaft, draws fuel
from the tank and supplies it to the carburetor float chamber at 0.2-0.3
bar (3-4 psi).
The intake manifold is manufactured from aluminum and features a single
plenum dividing into four individual runners. A hot air choke system or
electric choke is fitted depending on the market and emissions
requirements. The G161Z variant features recalibrated carburetor jetting
and revised throttle linkage for improved emissions compliance and
driveability.
The lubrication system is a forced-feed, wet-sump type utilizing a
gear-type oil pump mounted to the front of the crankshaft. The pump is
driven directly by the crankshaft, ensuring immediate oil pressure upon
startup. Oil is drawn from a stamped steel oil pan through a strainer
before pressurization. A full-flow spin-on oil filter is mounted
externally on the cylinder block.
The system supplies lubricant to the crankshaft main bearings,
connecting rod bearings, camshaft bearings, rocker arm shaft, and timing
chain. The oil pump incorporates a pressure relief valve set between 3.5
and 4.2 bar (50-60 psi) at operating speed. The oil pan capacity
supports sustained operation with a dipstick on the side of the block
indicating oil level.
The cooling system is a pressurized, water-cooled setup utilizing a
centrifugal water pump driven by the engine’s accessory belt. A wax-type
thermostat with a rated opening temperature of 82°C (180°F) regulates
the engine operating temperature. Coolant circulates through the
cast-iron cylinder block and aluminum cylinder head before passing
through a cross-flow radiator.
A belt-driven cooling fan, mounted to the water pump pulley, provides
airflow across the radiator. The system incorporates an expansion tank
or radiator overflow reservoir. The cooling system capacity accommodates
sustained operation under varied ambient temperatures.
Ignition System: The engine utilizes a distributor-based ignition system
with mechanical centrifugal advance and vacuum advance control. The
distributor is mounted on the cylinder head, driven by the camshaft, and
contains the breaker points (early models) or electronic ignition module
(late models). Ignition timing is set at 6 degrees before top dead
center at 800 rpm idle speed with the vacuum advance hose disconnected.
The ignition coil is a standard oil-filled type producing approximately
20-25 kV output.
Timing System: The camshaft is driven by a single-row timing chain. The
chain connects the crankshaft sprocket to the camshaft sprocket, with an
automatic spring-loaded chain tensioner maintaining correct chain
tension. The timing chain is designed for the life of the engine with no
scheduled replacement interval. The timing cover incorporates the chain
housing and the front engine seals.
Intake System: Air is drawn through a dry-type paper element air filter
housed in a stamped steel or plastic air cleaner assembly. The air
cleaner mounts directly above the carburetor. A heat riser tube directs
warm air from the exhaust manifold to the air cleaner during cold
starts. A crankcase ventilation hose connects the valve cover to the air
cleaner, routing blow-by gases into the intake system for combustion
(closed PCV system).
Exhaust System: The exhaust system incorporates a cast-iron manifold
collecting gases from the four cylinders. The manifold is bolted to the
cylinder head with steel gaskets. A single exhaust pipe connects the
manifold to the catalytic converter (on emissions-equipped variants) and
a muffler. The system includes the oxygen sensor on later
emissions-controlled applications.
Emission Control: Late-production G161 and G161Z engines incorporate
exhaust gas recirculation (EGR) systems, evaporative emissions control
(charcoal canister), and positive crankcase ventilation (PCV). The G161Z
variant specifically was calibrated to meet more stringent emissions
standards of the late 1970s.
Overall Engine Length: 610 mm (24.0 in) from fan to flywheel.
Overall Engine Width: 550 mm (21.7 in).
Overall Engine Height: 640 mm (25.2 in) from oil pan bottom to rocker
cover top.
Dry Weight: 125 kg (276 lb), inclusive of the intake manifold, exhaust
manifold, carburetor, distributor, starter motor, and alternator.
Engine Oil Capacity (with Filter): 4.0 liters (4.2 U.S. qt, 3.5 imperial
qt).
Engine Oil Specification: API SE, SF, or SG grade; SAE 10W-30, 10W-40,
or 20W-50.
Coolant Capacity: 7.0 liters (7.4 qt) inclusive of the radiator and
engine block.
Coolant Specification: Ethylene glycol-based antifreeze mixed 50:50 with
distilled water.
Thermostat Opening Temperature: 82°C (180°F).
Spark Plug Type: NGK BP6ES or equivalent.
Spark Plug Gap: 0.7-0.8 mm (0.028-0.031 in).
Spark Plug Replacement Interval: 20,000 km (12,000 mi).
Intake Valve Clearance (Hot): 0.20 mm (0.008 in).
Exhaust Valve Clearance (Hot): 0.25 mm (0.010 in).
Valve Clearance Inspection Interval: 25,000 km (15,000 mi) or annually.
Ignition Timing: 6 degrees before top dead center @ 800 rpm idle.
Ignition Points Gap (early models): 0.45-0.55 mm (0.018-0.022 in).
Dwell Angle (early models): 49-55 degrees.
Fuel Filter Replacement Interval: 20,000 km (12,000 mi).
Air Filter Replacement Interval: 20,000 km (12,000 mi) or annually.
Carburetor Adjustment: Idle mixture screw set at 1.5-2.0 turns from
lightly seated.
Cylinder Head Bolts, Step 1: 30 Nm (3.1 kgf-m, 22 lb-ft).
Cylinder Head Bolts, Step 2: 50 Nm (5.1 kgf-m, 37 lb-ft).
Cylinder Head Bolts, Step 3: 70 Nm (7.1 kgf-m, 52 lb-ft).
Main Bearing Cap Bolts: 70 Nm (7.1 kgf-m, 52 lb-ft).
Connecting Rod Cap Bolts: 45 Nm (4.6 kgf-m, 33 lb-ft).
Flywheel Bolts: 55 Nm (5.6 kgf-m, 41 lb-ft).
Crankshaft Pulley Bolt: 100 Nm (10.2 kgf-m, 74 lb-ft).
Camshaft Sprocket Bolt: 50 Nm (5.1 kgf-m, 37 lb-ft).
Camshaft Bearing Cap Bolts: 20 Nm (2.0 kgf-m, 15 lb-ft).
Rocker Arm Shaft Bolts: 25 Nm (2.5 kgf-m, 18 lb-ft).
Intake Manifold Bolts: 20 Nm (2.0 kgf-m, 15 lb-ft).
Exhaust Manifold Nuts: 25 Nm (2.5 kgf-m, 18 lb-ft).
Oil Pump Mounting Bolts: 15 Nm (1.5 kgf-m, 11 lb-ft).
Oil Pan Bolts: 10 Nm (1.0 kgf-m, 7 lb-ft).
Timing Chain Tensioner Bolt: 20 Nm (2.0 kgf-m, 15 lb-ft).
Spark Plugs: 20 Nm (2.0 kgf-m, 15 lb-ft).
Oil Filter (Spin-on Type): 15 Nm (1.5 kgf-m, 11 lb-ft).
Fuel Pump Mounting Bolts: 15 Nm (1.5 kgf-m, 11 lb-ft).
Carburetor Mounting Nuts: 15 Nm (1.5 kgf-m, 11 lb-ft).
Starter Motor Mounting Bolts: 35 Nm (3.6 kgf-m, 26 lb-ft).
Alternator Mounting Bolts: 30 Nm (3.1 kgf-m, 22 lb-ft).
The Isuzu G161 and G161Z engines were utilized across Isuzu's passenger
car, pickup truck, and commercial vehicle lineups throughout the 1970s
and early 1980s.
Isuzu Passenger Cars
Isuzu Gemini (Bellett, PF series): 1974-1981, with the G161 in base
models and G161Z in higher trim levels.
Isuzu Gemini (I-Mark): Late 1970s to early 1980s, North American and
export markets.
Isuzu Florian: Select export markets receiving the 1.6-liter powerplant.
Isuzu Pickup Trucks and Commercial Vehicles
Isuzu Faster (KB series): 1972-1982, with G161 and G161Z in various cab
and chassis configurations.
Isuzu Pickup / Isuzu P'Up: North American market pickup from 1972
through 1982.
Chevrolet LUV (Light Utility Vehicle): 1972-1982, badge-engineered Isuzu
Faster sold through Chevrolet dealerships in North America.
Bedford KB: 1972-1982, badge-engineered Isuzu Faster sold under the
Bedford brand in the United Kingdom and Commonwealth markets.
Industrial and Marine Applications
Isuzu Industrial Power Units: Stationary engine versions for pumps,
generators, and small industrial equipment.
Marine Propulsion: Small boat applications using marinized G161 engines.
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