Toyota 3AU Specifications
| Engine Model: Toyota 3AU |
| Engine Type: 4-cycle inline 4-cylinder SOHC 8-valve liquid-cooled gasoline |
| Total Displacement: 88.6 cu.in (1.45 L) |
| Rated Engine Power: 83 Hp (61 kW) at 5600 rpm |
| Fuel System Type: Two-barrel downdraft carburetor |
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The Toyota 3A-U is a 1.5-liter, naturally aspirated
inline-four gasoline engine belonging to the Toyota A series. Introduced in 1979
as a replacement for the older T engine, the 3A-U was developed specifically for
the Japanese Domestic Market (JDM) to meet the stringent emissions regulations
of the era. The “U” designation indicates the presence of Toyota’s TTC-C (Toyota
Total Clean Catalytic) system, which combined a catalytic converter with an air
injection system to achieve compliance with Japan’s 1978 emissions standards.
This engine represented Toyota’s shift toward cleaner, more fuel-efficient
powerplants for its compact car lineup.
The 3AU is a single overhead camshaft (SOHC) engine with eight valves - two
valves per cylinder - a configuration that emphasizes low- to mid-range torque
and mechanical simplicity. The engine utilizes a cast iron cylinder block with
an aluminum alloy cylinder head, a hybrid construction that provides durability
while managing overall mass. Fuel delivery is provided by a single two-barrel
downdraft carburetor.
The timing system is belt-driven, and the engine is of non-interference design,
a feature that provides a safety margin against catastrophic damage in the event
of timing belt failure. The compact dimensions of the 3A-U, enabled by its
siamesed cylinder design, made it suitable for the small engine bays of Toyota’s
compact cars of the period. The engine was installed in the Toyota Corolla,
Sprinter, Tercel, Carina, and first-generation MR2, serving as a fuel-efficient
and emissions-compliant powerplant.
The 3A-U is a water-cooled, four-stroke, naturally aspirated gasoline engine
configured for longitudinal or transverse mounting depending on the vehicle
application. Its design emphasizes fuel efficiency, emissions compliance, and
compact packaging.
Engine Type: Inline-4, 4-cycle, water-cooled, naturally aspirated.
Displacement: 1,452 cc (88.6 cu.in).
Bore and Stroke: 77.5 mm (3.05 in) x 77.0 mm (3.03 in).
Compression Ratio: 9.0:1.
Valvetrain: SOHC, 8-valve (2 valves per cylinder) with belt drive.
Fuel System: Single two-barrel downdraft carburetor.
Firing Order: 1-3-4-2.
Maximum Power: 61 kW (83 hp) at 5,600 rpm.
Maximum Torque: 118 Nm (87 lb-ft) at 3,600 rpm.
Idle Speed: 750 ± 50 rpm.
Engine Redline: 5,600-6,000 rpm (application dependent).
The cylinder block is constructed from gray cast iron,
a material selected for its exceptional rigidity, vibration-damping properties,
and long-term dimensional stability. The block utilizes a siamesed cylinder
design, in which adjacent cylinders share a common wall, eliminating water
jacket passages between cylinders. This design reduces overall block length,
contributing to the engine’s compact dimensions of approximately 550 mm (21.7
in) in length.
Cast-in-place cylinder bores are machined directly into the iron casting. The
block incorporates five main bearing webs with two-bolt main bearing caps. The
crankshaft is supported by five bearings and is constructed from cast iron. A
stamped steel oil pan is sealed to the lower crankcase, providing the oil
reservoir. The block design incorporates water passages around the outer
perimeter of the cylinders to provide adequate cooling despite the siamesed
construction.
Block Material: Gray cast iron
Bore Diameter (finished): 77.5 mm (3.05 in)
Main Bearing Caps: Cast iron, two-bolt design
Cylinder Bore Deformation Limit: 0.05 mm (0.0020 in)
The cylinder head is manufactured from aluminum alloy,
a selection that reduces overall engine mass and improves heat dissipation from
the combustion chambers. The SOHC valvetrain actuates eight valves - two valves
per cylinder - through a system of rocker arms. The rocker arms incorporate
adjustment screws for manual valve clearance setting. The camshaft is driven by
a reinforced rubber timing belt from the crankshaft, with an automatic
spring-loaded tensioner maintaining belt tension.
The combustion chambers are of a compact hemispherical design that promotes
efficient flame propagation. The cylinder head incorporates the TTC-C emissions
control system, including air injection passages that direct secondary air into
the exhaust ports to promote oxidation of hydrocarbons and carbon monoxide in
the catalytic converter. The engine is of non-interference design; piston crowns
and valves occupy separate spaces within the combustion chamber, meaning that
timing belt failure does not result in valve-to-piston contact.
Head Material: Aluminum alloy
Valve Configuration: SOHC, 2 valves per cylinder with rocker arms
Valve Diameter (Intake): 38.0 mm (1.50 in)
Valve Diameter (Exhaust): 32.0 mm (1.26 in)
Valve Stem Diameter: 7.0 mm (0.28 in)
Valve Seat Angle: 45 degrees
Non-Interference Design: Yes
The 3AU employs a single two-barrel downdraft
carburetor manufactured by Aisan or similar supplier. The carburetor features a
primary and secondary barrel, with the secondary barrel opening under increased
throttle demand to provide additional airflow and fuel delivery. The carburetor
incorporates a choke system for cold-start enrichment and various emission
control devices, including a deceleration fuel cut system and a throttle
positioner to reduce hydrocarbon emissions during deceleration.
A mechanical fuel pump mounted on the cylinder head draws fuel from the fuel
tank and delivers it to the carburetor float chamber. The carburetor is equipped
with an automatic choke mechanism on most variants, utilizing a bi-metallic coil
and electric heater for cold-start operation. The TTC-C emissions system
includes an air pump that injects secondary air into the exhaust ports and a
three-way catalytic converter to reduce emissions.
Carburetor Type: Single two-barrel downdraft (Aisan).
Fuel Pump Type: Mechanical, diaphragm-type.
Fuel Requirement: 87 octane (Research Octane Number 91) minimum.
Emissions System: TTC-C (Toyota Total Clean Catalytic) with air injection and
catalytic converter.
The lubrication system is a fully pressurized, wet-sump
design utilizing a gear-type oil pump mounted to the front of the crankshaft.
The oil pump draws lubricant from the stamped steel oil pan through a mesh
strainer and circulates it through a full-flow, replaceable oil filter before
entering the main oil gallery. From the gallery, pressurized oil is distributed
to the crankshaft main bearings, connecting rod bearings, camshaft bearings,
rocker arm assemblies, and timing belt tensioner.
A pressure relief valve integrated into the oil pump maintains system pressure
within operational limits to prevent over-pressurization during cold starts. The
lubrication system is designed to provide adequate protection across the
engine’s operating temperature range with the specified oil viscosity.
Oil Type: SAE 10W-30 or 5W-30 (API SF, SG, or higher)
Oil Capacity (with filter): 3.5 liters (3.7 US qt)
Oil Pressure (at 3,000 rpm): 294-392 kPa (42.6-56.9 psi)
Oil Pump Type: Gear-type, crankshaft-driven
Oil Filter Type: Spin-on, full-flow
The cooling system is a pressurized, liquid-cooled
design employing a cross-flow aluminum or copper-brass radiator with an
engine-driven cooling fan. A centrifugal-type water pump, driven by the timing
belt, circulates coolant through the engine block, cylinder head, and heater
core. A wax-pellet thermostat regulates coolant flow to maintain optimal
operating temperature, with a bypass circuit that allows the engine to warm
rapidly by circulating coolant only within the engine until the thermostat
opens.
The cooling system is designed to provide uniform cooling across the cast iron
block and aluminum head interface, maintaining consistent thermal expansion
characteristics across the cylinder head gasket sealing surfaces.
Coolant Type: Ethylene-glycol based antifreeze with corrosion inhibitors
Coolant Capacity: 4.5-5.5 liters (4.8-5.8 US qt)
Thermostat Opening Temperature: 82-86 °C (180-187 °F)
Thermostat Full-Open Temperature: 95 °C (203 °F)
Radiator Cap Pressure: 88-108 kPa (12.8-15.7 psi)
Water Pump Type: Centrifugal, timing belt-driven
| Intake and Exhaust Systems |
Intake System: Cast aluminum intake manifold with a
single two-barrel carburetor mounting flange. The intake manifold incorporates
water passages for carburetor base heating to improve fuel vaporization during
cold operation. An air cleaner housing with a dry-type paper filter element is
mounted above the carburetor.
Exhaust System: Cast iron exhaust manifold with individual runners collecting
into a single downpipe. The TTC-C system includes an air injection manifold that
introduces secondary air into each exhaust port. A three-way catalytic converter
is mounted in the exhaust system, with an oxygen sensor on later variants
providing feedback for air-fuel ratio control.
Ignition System: Distributor-based ignition system with
a camshaft-driven distributor. The distributor houses the ignition rotor, cap,
and mechanical and vacuum advance mechanisms. A separate ignition coil is
mounted on the engine or firewall. The TTC-C system incorporates ignition timing
modifications to assist catalytic converter warm-up.
Timing Drive: A reinforced rubber timing belt with integral teeth drives the
camshaft from the crankshaft sprocket. An automatic spring-loaded tensioner
maintains belt tension. The timing belt is a scheduled maintenance item with a
defined replacement interval. The engine’s non-interference design ensures that
valve-to-piston contact does not occur if the belt fails.
Overall Length: 550 mm (21.7 in)
Overall Width: 620 mm (24.4 in)
Overall Height: 680 mm (26.8 in)
Dry Weight (complete engine): 105-115 kg (231-254 lb)
Oil Change Interval: 10,000 km (6,200 mi) under normal
driving conditions.
Oil Change Interval: 5,000 km (3,100 mi) under severe conditions.
Oil Filter Change: At every oil change.
Timing Belt Replacement: 100,000 km (60,000 mi) or 5 years.
Engine Coolant Replacement: 40,000 km (25,000 mi) or 2 years.
Spark Plug Replacement: 20,000 km (12,500 mi) for standard plugs.
Spark Plug Type: NGK BPR5EYA or Denso W16EXR-U.
Spark Plug Gap: 0.7-0.8 mm (0.028-0.031 in).
Drive Belt (Accessory) Inspection: Every 10,000 km (6,200 mi) for tension,
cracking, and glazing.
Air Filter Replacement: 20,000 km (12,500 mi) or as indicated by inspection.
Fuel Filter Replacement: 20,000 km (12,500 mi) for external filter types.
Valve Clearance Adjustment: Inspect and adjust every 20,000 km (12,500 mi).
Intake Valve Clearance: 0.15-0.25 mm (0.0059-0.0098 in) cold.
Exhaust Valve Clearance: 0.25-0.35 mm (0.0098-0.0138 in) cold.
Idle Speed Adjustment: 750 ± 50 rpm with no electrical or accessory load.
Cylinder Head Bolts (M10 x 1.25), 1st pass: 20-25 Nm
(15-18 lb-ft).
Cylinder Head Bolts (M10 x 1.25), 2nd pass: 50-55 Nm (37-41 lb-ft).
Main Bearing Cap Bolts (M10 x 1.25): 45-50 Nm (33-37 lb-ft).
Connecting Rod Cap Bolts (M8 x 1.0): 25-28 Nm (18-21 lb-ft).
Camshaft Bearing Cap Bolts (M8 x 1.25): 18-22 Nm (13-16 lb-ft).
Rocker Arm Shaft Bolts (M8 x 1.25): 18-22 Nm (13-16 lb-ft).
Intake Manifold Bolts (M8 x 1.25): 16-20 Nm (12-15 lb-ft).
Exhaust Manifold Nuts (M8 x 1.25): 16-20 Nm (12-15 lb-ft).
Spark Plugs: 18-22 Nm (13-16 lb-ft).
Oil Pan Bolts (M6 x 1.0): 8-10 Nm (71-89 lb-in).
Water Pump Bolts (M6 x 1.0): 8-10 Nm (71-89 lb-in).
Timing Belt Tensioner Bolt (M8 x 1.25): 18-22 Nm (13-16 lb-ft).
Crankshaft Pulley Bolt (M14 x 1.5): 130-140 Nm (96-103 lb-ft).
Flywheel / Drive Plate Bolts (M10 x 1.25): 70-75 Nm (52-55 lb-ft).
The Toyota 3A-U engine was utilized exclusively in
Japanese Domestic Market vehicles throughout its production period from 1979 to
1989.
Toyota Corolla (AE70): 1979-1983.
Toyota Corolla (AE81, AE85): 1983-1987.
Toyota Sprinter / Trueno / Levin (AE70, AE85): 1979-1987.
Toyota Tercel / Corsa / Corolla II (AL12): 1979-1982.
Toyota Tercel / Corsa / Corolla II (AL21, AL25): 1982-1989.
Toyota Carina (AA60): Selected variants with 3A-U engine.
Toyota Corona (AT140, AT150): Selected variants with 3A-U engine.
Toyota MR2 (AW10): 1984-1989 (entry-level 1.5-liter variant).
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