Isuzu G161Z Specifications
| Engine Model: Isuzu G161Z |
| Engine Type: 4-stroke in-line 4-cylinder 8-valve SOHC liquid-cooled gasoline |
| Total Displacement: 96.7 cu.in (1.58 L) |
| Rated Engine Power: 80-100 Hp (59-74 kW) at 5400 rpm |
| Fuel System Type: Carburetor |
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The Isuzu G161Z is a 1.6-liter inline
4-cylinder petrol engine from the G-Z series, representing Isuzu’s
transition from older OHV (overhead valve) designs to a more modern SOHC
(Single Overhead Camshaft) configuration. Produced primarily during the
1970s and 1980s, this engine became the standard powerplant for the
Isuzu Gemini (Bellett Gemini) and early Chevrolet Chevette models across
global markets.
The G161Z combined a high-nickel cast iron cylinder block with an
aluminum alloy cross-flow cylinder head, utilizing a timing chain rather
than a belt-driven camshaft, which contributed to its reputation for
durability and low maintenance. The engine was produced in multiple
compression ratios and power outputs to suit different market
regulations, with Australian, Japanese, and European variants receiving
different carburetion and emissions equipment. Its robust 5-main-bearing
crankshaft design provided smooth operation at higher engine speeds.
Engine Family: Isuzu G-Z series
Engine Code: G161Z
Configuration: Inline 4-cylinder, longitudinally mounted, rear-wheel
drive
Displacement: 1584 cc (96.7 cu.in)
Bore: 82.0 mm (3.23 in)
Stroke: 75.0 mm (2.95 in)
Compression Ratio: 8.7:1 (std)
Compression Ratio: 9.4:1 (high)
Firing Order: 1-3-4-2
Valvetrain Type: Single Overhead Camshaft, 8 valves (2 per cylinder)
Valvetrain Drive: Roller-type timing chain with mechanical tensioner
Maximum Power (8.7:1 CR): 59-63 kW (80-86 hp) at 5200-5400 rpm
Maximum Power (9.4:1 CR): 74 kW (100 hp) at 6000 rpm
Maximum Torque (8.7:1 CR): 120-125 Nm (89-92 lb-ft) at 3400 rpm
Maximum Torque (9.4:1 CR): 130 Nm (96 lb-ft) at 3800 rpm
Engine Redline: 6200 rpm
Idle Speed: 750-800 rpm ± 50 rpm; 800 rpm for ignition timing setting
The cylinder block is constructed from cast iron with a high nickel
content added to the metallurgical formulation, enhancing wear
resistance and extending service life under sustained operation. The
block features a deep-skirt design extending below the crankshaft
centerline, providing structural rigidity for the rotating assembly.
Five main bearings support the forged or cast iron crankshaft, a design
feature that provides superior high-rpm smoothness compared to 3-bearing
or 4-bearing configurations found in competitor engines of the era.
Cylinder bores are machined directly into the parent cast iron material
without replaceable liners, with a final plateau-honed finish to promote
oil retention and piston ring sealing. The block incorporates an
integral oil gallery running the full length of the cylinder bank on the
right-hand side, supplying lubricant to the main bearings, camshaft
bearings, and valvetrain. The engine mounting bosses are cast into the
block sides, with configuration specific to the Gemini/Chevette chassis.
The cylinder head is manufactured from cast aluminum alloy utilizing a
cross-flow design, with the intake manifold positioned on the right side
and the exhaust manifold on the left side in rear-wheel-drive
applications. The SOHC arrangement operates eight valves via rocker arms
that pivot on a fixed rocker shaft. Valve clearances are adjustable
using threaded adjusters and locknuts on the rocker arms, requiring
periodic maintenance. Intake valve diameter is 40.0 mm (1.57 in);
exhaust valve diameter is 34.0 mm (1.34 in).
Valve stems are 8.0 mm (0.31 in) in diameter. Valve clearances are
measured with the engine hot (normal operating temperature). Hot
clearance specification: intake 0.15 mm (0.006 in), exhaust 0.25 mm
(0.010 in). The combustion chamber is a hemispherical design promoting
effective flame propagation. The timing chain housing is cast integrally
with the cylinder head and front cover. Rocker arms are forged steel
units with hardened contact faces at both the camshaft lobe and valve
stem tip.
The fuel system utilizes a single downdraft carburetor, manufactured by
either Nikki or Hitachi depending on production date and market. The
carburetor incorporates a manual or water-operated automatic choke, a
mechanical accelerator pump, and a power valve enrichment circuit. Fuel
delivery is supplied by a mechanical diaphragm-type fuel pump mounted on
the side of the cylinder head, actuated by an eccentric lobe on the
camshaft.
The pump operates at a fuel pressure of 0.20-0.25 bar (2.9-3.6 psi) and
incorporates a sediment bowl with a removable mesh filter. A spacer
block is installed between the fuel pump and cylinder head to insulate
the pump from engine heat, with paper gaskets on both sides of the
spacer. Later emissions-controlled variants for certain markets received
a single-point throttle-body injection system, though carbureted
versions remain the most common configuration for the G161Z worldwide.
The lubrication system is a wet-sump configuration utilizing a
rotor-type oil pump mounted on the front of the crankshaft, driven
directly by a keyed drive sleeve. The pump draws oil through a fixed
mesh pickup screen located in the stamped steel oil pan and delivers it
through a full-flow spin-on oil filter mounted on the right side of the
cylinder block. System capacity with filter replacement is 3.5 liters
(3.7 qt).
The oil pan incorporates a baffle plate to maintain oil pickup during
cornering. Recommended oil viscosity is SAE 10W-30 or 10W-40 meeting API
SE, SF, or SG specifications for original equipment. Oil pressure at
operating temperature at 3000 rpm is specified at 3.0-4.0 bar (43.5-58.0
psi), while hot idle pressure is maintained at a minimum of 0.5 bar (7.3
psi). A pressure relief valve integrated into the oil pump housing
limits maximum system pressure to4.5 bar (65.3 psi).
The cooling system operates under pressure with a sealed expansion tank
or a radiator cap rated at 0.9 bar (13.1 psi). Coolant circulation is
driven by a centrifugal water pump mounted on the front of the cylinder
block, driven by a V-belt from the crankshaft pulley operating in
conjunction with the alternator. System total capacity is 6.0 liters
(6.3 qt) including the radiator and engine block. A wax-pellet
thermostat is housed in a housing at the water pump inlet, commencing
opening at 82°C (180°F) and reaching full open at 95°C (203°F).
An engine-driven cooling fan is mounted on the water pump pulley,
equipped with a fan clutch on certain variants. Coolant specified is
ethylene glycol-based, mixed at a 40:60 to 50:50 ratio with distilled
water. The cylinder block incorporates full-length water jackets
surrounding each cylinder, with coolant directed from the block to the
cylinder head through passages aligned with the head gasket. The
aluminum cylinder head requires coolant maintenance to prevent internal
corrosion and scale buildup.
| Intake and Exhaust Systems |
Exhaust System: Cast iron exhaust manifold with a single outlet flange.
Emissions-controlled variants incorporate exhaust gas recirculation
(EGR) ports and a catalytic converter in certain markets.
Intake System: Dry-type paper element air filter housed in a sheet metal
canister mounted on the carburetor. A hot air intake system drawing warm
air from the exhaust manifold shield is incorporated on cold-climate
specifications.
Ignition System: Distributor-type ignition with mechanical centrifugal
advance and vacuum advance diaphragm. The distributor is driven by a
helical gear on the exhaust camshaft. Spark plugs are specified with a
gap of 0.7-0.8 mm (0.028-0.031 in). Ignition timing is set at 6° before
top dead center (BTDC) at 800 rpm idle with the vacuum advance line
disconnected and plugged.
Emission Control: Positive crankcase ventilation (PCV) system with a
flow control valve connected to the intake manifold. Evaporative
emissions control system with charcoal canister on later variants.
Charging System: 12-volt electrical system with a belt-driven alternator
rated at 40-55 amps depending on vehicle equipment specification.
Overall Length: 670 mm (26.38 in).
Overall Width: 590 mm (23.23 in).
Overall Height: 660 mm (25.98 in).
Dry Engine Weight (without coolant, oil, flywheel, and accessories): 125
kg (276 lb).
Fully Dressed Weight (with carburetor, intake and exhaust manifolds,
alternator, starter, distributor, and all ancillaries): 148 kg (326 lb).
Oil Change Interval: 5000 km (3107 mi) or 6 months under normal service;
3000 km (1864 mi) under severe duty conditions. Oil Filter Replacement:
Replace at every oil change interval. Spark Plug Replacement: 20,000 km
(12,427 mi) for conventional copper-core plugs. Fuel Filter Replacement:
Inspect sediment bowl at every oil change; replace inline filter (where
fitted) every 30,000 km (18,641 mi).
Valve Clearance Adjustment: Inspect and adjust every 20,000 km (12,427
mi); adjustment performed with engine at normal operating temperature:
intake 0.15 mm (0.006 in), exhaust 0.25 mm (0.010 in). Timing Chain: No
replacement interval specified; inspect timing chain tensioner for wear
every 80,000 km (49,710 mi); replace chain and tensioner if rattling is
evident on cold startup.
Air Filter Replacement: 20,000 km (12,427 mi) or as indicated by visual
inspection. Coolant Replacement: 40,000 km (24,855 mi) or 24 months.
Drive Belt (Alternator/Water Pump): Inspect every 10,000 km (6214 mi);
replace if cracking, glazing, or fraying is evident. Carburetor Idle
Adjustment: Adjust idle speed to 750-800 rpm; adjust idle mixture screw
for maximum vacuum or smooth operation.
Cylinder Head Bolts (M10 x 1.25), Stage 1: 25 Nm (18 lb-ft)
Cylinder Head Bolts (M10 x 1.25), Stage 2: 50 Nm (37 lb-ft)
Cylinder Head Bolts (M10 x 1.25), Stage 3: 70 Nm (52 lb-ft)
Main Bearing Cap Bolts (M10 x 1.25), Stage 1: 30 Nm (22 lb-ft)
Main Bearing Cap Bolts (M10 x 1.25), Stage 2: 55 Nm (41 lb-ft)
Connecting Rod Cap Nuts (M8 x 1.0): 35 Nm (26 lb-ft)
Flywheel Bolts (M10 x 1.25): 60 Nm (44 lb-ft)
Camshaft Sprocket Bolt (M12 x 1.5): 50 Nm (37 lb-ft)
Rocker Arm Shaft Bolts (M8 x 1.25): 20 Nm (15 lb-ft)
Rocker Arm Adjuster Locknuts (M8 x 1.0): 15 Nm (11 lb-ft)
Intake Manifold Nuts (M8 x 1.25): 20 Nm (15 lb-ft)
Exhaust Manifold Nuts (M8 x 1.25): 25 Nm (18 lb-ft)
Spark Plugs: 25 Nm (18 lb-ft)
Engine Oil Drain Plug: 35 Nm (26 lb-ft)
Timing Chain Tensioner Bolts (M6 x 1.0): 10 Nm (7 lb-ft)
Water Pump Bolts (M8 x 1.25): 20 Nm (15 lb-ft)
Fuel Pump Mounting Nuts (M8 x 1.25): 15 Nm (11 lb-ft)
Distributor Mounting Clamp Bolt (M8 x 1.25): 15 Nm (11 lb-ft)
Isuzu Gemini (PF50, PF60, JT150): 1974-1987, longitudinal front-engine,
rear-wheel drive; G161Z as standard engine from introduction through
series production.
Holden Gemini (TX, TC, TD, TE, TF, TG): 1975-1986, Australian market;
G161Z as the primary powerplant for 1.6-liter variants; 8.7:1
compression ratio for standard models, 9.4:1 for high-compression
variants.
Chevrolet Chevette: 1975-1982, various international markets including
South America and Europe; G161Z in 1.6-liter petrol versions.
Isuzu 117 Coupe: 1977-1981, base 1600 model variant utilizing G161Z with
9.4:1 compression ratio and twin-carburetor configuration in certain
markets.
Isuzu Fargo (WFR): 1979-1983, early petrol variants of this light
commercial van; G161Z in low-compression 8.7:1 form for commercial duty
cycles.
Isuzu Faster / KB (TF series): Limited application in early pickup
variants for select Asian markets before transition to 4ZE1 engine
family.
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