Volkswagen AAB Specifications
| Engine Model: Volkswagen AAB |
| Engine Type: 4-cycle inline 5-cylinder SOHC 10-valve liquid-cooled diesel |
| Total Displacement: 144.6 cu.in (2.37 L) |
| Rated Engine Power: 77 Hp (57 kW) at 3700 rpm |
| Fuel System Type: Indirect injection |
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The AAB is distinguished within the Volkswagen diesel
lineage by its five-cylinder configuration and its adherence to indirect
injection (IDI) technology. The engine displaces 2,370 cc through a bore and
stroke of 79.5 mm and 95.5 mm respectively, producing an undersquare design that
emphasizes low-speed torque production. The valvetrain is a belt-driven SOHC
operating two valves per cylinder via hydraulic bucket tappets, which eliminate
the need for periodic manual valve clearance adjustments.
The fuel system employs a Bosch VE-type mechanical distributor injection pump, a
robust and serviceable unit that delivers fuel to precombustion chambers (swirl
chambers) within the cylinder head. The AAB is an interference engine; a timing
belt failure results in piston-to-valve contact and significant internal damage.
The engine’s cooling system incorporates a timing belt-driven water pump, a
design feature that necessitates water pump replacement during timing belt
service to prevent future belt contamination from coolant leaks.
Power output is modest at 57 kW (78 hp), but the engine produces peak torque of
164 Nm at a low 1,800 rpm, providing effective pulling power for laden vehicles.
The AAB is recognized for its mechanical reliability, straightforward
serviceability, and characteristic five-cylinder exhaust note, though its
indirect injection architecture limits fuel efficiency and power density
compared to later direct-injection diesel engines.
Engine Type: Inline-5, naturally aspirated diesel, longitudinal mounting.
Displacement: 2,370 cc (144.6 cu.in).
Bore: 79.5 mm (3.13 in).
Stroke: 95.5 mm (3.76 in).
Compression Ratio: 22.5:1.
Management System: Mechanical with Bosch VE distributor injection pump.
Fuel System: Indirect injection with precombustion chambers.
Firing Order: 1-2-4-5-3.
Max Power: 57 kW (78 PS; 77 hp) @ 3,700 rpm.
Max Torque: 164 Nm (121 lb-ft) @ 1,800 rpm.
Redline: 4,600 rpm.
The cylinder block is constructed from cast iron with
an open-deck design, providing the rigidity necessary for diesel operation under
sustained high-load conditions. The inline-five configuration requires a longer
block casting than inline-four units, with five cylinder bores machined directly
into the cast iron without separate liners. The block incorporates a deep-skirt
construction extending below the crankshaft centerline, contributing to
structural stiffness.
The crankshaft is supported by six main bearings, an additional bearing compared
to inline-four engines, providing enhanced support for the longer rotating
assembly. The block includes integral oil galleries for the valvetrain and
crankshaft bearings. The water jacket surrounds the cylinders fully, with
coolant passages designed to provide uniform cooling across all five cylinders.
The engine mounts are cast into the block sides, with provisions for both
conventional and Syncro (all-wheel-drive) chassis configurations. The block also
houses the oil pump, which is driven directly by the crankshaft.
The cylinder head is a single casting in gray cast
iron, a material chosen for its thermal stability and compatibility with the
cast iron block. The SOHC valvetrain operates two valves per cylinder - one
intake and one exhaust - for a total of ten valves. The camshaft is driven by a
toothed timing belt and acts directly on hydraulic bucket tappets, which in turn
actuate the valves.
The hydraulic tappets automatically maintain zero valve clearance, eliminating
manual adjustment. The combustion system utilizes indirect injection with
precombustion chambers (swirl chambers) located within the cylinder head. Each
cylinder features a separate precombustion chamber insert, into which fuel is
injected. The design promotes swirl and mixing of fuel and air prior to main
combustion, reducing combustion noise and allowing for the high compression
ratio.
Valves: 10 total (5 intake, 5 exhaust)
Intake Valve Diameter: 34.0 mm (1.34 in)
Exhaust Valve Diameter: 31.0 mm (1.22 in)
Valve Stem Diameter: 8.0 mm (0.31 in) for both intake and exhaust
Valve Seat Material: High-strength alloy steel inserts
The cylinder head gasket is a composite fiber and steel construction, designed
to accommodate the thermal expansion characteristics of the cast iron block and
head. The intake and exhaust ports are positioned on opposite sides of the
cylinder head in a cross-flow arrangement.
The fuel system is a mechanically governed indirect
injection system centered on a Bosch VE-type distributor injection pump. The
pump is driven by a separate toothed belt from the camshaft, operating
independently of the timing belt that drives the camshaft. This arrangement
requires two separate belts: one for the camshaft and a second for the injection
pump.
The VE pump combines a low-pressure transfer pump, a high-pressure radial piston
pump, and a mechanical governor within a single housing. Fuel is drawn from the
tank through a water separator and filter, then pressurized within the pump to
injection pressures of approximately 400-500 bar (5,800-7,250 psi). From the
pump, high-pressure fuel is distributed to the five individual injectors via
steel injection lines.
The injectors are mechanical units with a spring-loaded pintle, set to open at a
calibrated cracking pressure. Fuel is injected into the precombustion chambers,
where initial combustion occurs before expanding into the main combustion
chamber. A cold-start advance mechanism on the injection pump advances injection
timing during engine warm-up to improve cold running.
The lubrication system is a pressurized, wet-sump
design with a gear-type oil pump driven directly by the crankshaft. The pump is
mounted within the front cover assembly and draws oil from a stamped steel oil
pan through a screened pickup tube.
A full-flow, spin-on oil filter is mounted
externally on the engine block. The system supplies oil to the six main
bearings, five connecting rod bearings, camshaft bearings, and hydraulic
tappets. The engine is equipped with an oil cooler integrated into the
oil filter housing, utilizing engine coolant to maintain oil temperature
under sustained load.
Oil Capacity (including filter): 5.5 liters (5.8 US qt).
Oil Pressure at 2,000 rpm: Minimum 200 kPa (29.0 psi).
Recommended Oil Viscosity: 15W-40 or 10W-40, API CD/CE or higher,
meeting diesel-specific specifications.
Oil Pump Type: Gear-type, crankshaft-driven.
The cooling system is a pressurized, closed-loop design
with a belt-driven water pump mounted to the front of the cylinder block. The
water pump is driven by the timing belt that also drives the camshaft, a design
requiring water pump replacement whenever the timing belt is serviced. Coolant
flows from the radiator through the pump, into the cylinder block passages
surrounding the cylinders, then upward through the cylinder head, and returns to
the radiator through a thermostat housing.
A wax-type thermostat maintains an operating temperature between 85-92 °C
(185-198 °F). The system utilizes a cross-flow radiator with an electric cooling
fan controlled by a thermostatic switch mounted in the radiator. A separate
heater circuit draws coolant from the rear of the cylinder head. Coolant
capacity for the engine and radiator is 8.5 liters (9.0 US qt).
Intake System: The intake manifold is a cast aluminum
unit with individual runners for each cylinder. The manifold incorporates a
swirl flap system in some variants to optimize air movement at low engine
speeds. A dry paper air filter is housed in a plastic air cleaner assembly.
Exhaust System: A cast iron exhaust manifold routes gases to a single exhaust
pipe. Depending on the production year and market, the system may include a
catalytic converter and a diesel oxidation catalyst. The exhaust system is
single-pipe with a single muffler.
Preheating System: The engine is equipped with a glow plug system for cold-start
assistance. Five glow plugs, one per cylinder, are controlled by a glow plug
relay and a coolant temperature sensor. The preheating time is automatically
regulated based on engine coolant temperature.
Emissions Control: The AAB meets Euro 1 emissions standards in its original
configuration, with later variants adapted to meet Euro 2 through the addition
of exhaust gas recirculation (EGR) and a diesel oxidation catalyst. The EGR
system routes a portion of exhaust gas back to the intake manifold through a
vacuum-actuated valve.
Overall Length: 790 mm (31.1 in).
Overall Width: 570 mm (22.4 in).
Overall Height: 700 mm (27.6 in).
Dry Weight (complete engine): 190 kg (419 lb) without accessories.
Dry Weight (complete engine): 210 kg (463 lb) with intake, exhaust, alternator,
and starter motor.
Timing Belt (Camshaft) Replacement Interval: 90,000 km
(56,000 mi) or 5 years.
Engine Oil Change Interval: 7,500 km (4,700 mi) or 12 months with mineral oil.
Engine Oil Change Interval: 10,000 km (6,200 mi) with semi-synthetic oil.
Oil Filter Replacement: With every oil change.
Fuel Filter Replacement Interval: 30,000 km (18,600 mi).
Glow Plug Inspection: Every 60,000 km (37,000 mi).
Coolant Replacement Interval: 40,000 km (25,000 mi) or 2 years.
Accessory Drive Belt Inspection: Every 10,000 km (6,200 mi).
Accessory Drive Belt Replacement: Every 60,000 km (37,000 mi).
Valve Clearance Check: Not required due to hydraulic tappets.
Injection Pump Belt Replacement Interval: 90,000 km (56,000 mi) concurrent with
timing belt service.
Water Pump Replacement: Recommended with each timing belt replacement due to
belt-driven design.
Cylinder Head Bolts: 60 Nm (44 lb-ft)
Connecting Rod Cap Bolts: 30 Nm (22 lb-ft)
Main Bearing Cap Bolts: 65 Nm (48 lb-ft)
Camshaft Bearing Cap Bolts: 20 Nm (15 lb-ft)
Intake Manifold Bolts: 20 Nm (15 lb-ft)
Exhaust Manifold Nuts: 25 Nm (18 lb-ft)
Glow Plugs: 15 Nm (11 lb-ft)
Fuel Injectors: 70 Nm (52 lb-ft)
Oil Filter: 25 Nm (18 lb-ft)
Oil Drain Plug: 35 Nm (26 lb-ft)
Crankshaft Pulley Bolt: 150 Nm (111 lb-ft)
Flywheel/Flexplate Bolts: 60 Nm (44 lb-ft)
Injection Pump Sprocket Bolt: 45 Nm (33 lb-ft)
The Volkswagen AAB engine was primarily utilized in the
Volkswagen Transporter T4 range from 1990 to 1998, serving as the entry-level
and mid-range diesel powerplant across multiple body styles and drive
configurations.
Volkswagen Transporter T4 (Van): The AAB powered the standard panel van and
cargo variants, providing a durable and fuel-efficient option for commercial
operators. The engine was available in both standard wheelbase (SWB) and long
wheelbase (LWB) configurations.
Volkswagen Caravelle (T4): The passenger-oriented Caravelle received the AAB in
base and mid-trim levels, offering seating for up to eight occupants with the
diesel’s low-end torque suited for laden travel.
Volkswagen Multivan (T4): The premium passenger variant utilized the AAB in
certain markets as a lower-cost alternative to the gasoline VR6 engine. The
Multivan applications often featured enhanced sound insulation to refine the
diesel’s operational noise.
Volkswagen California (T4): The camper van conversion received the AAB as the
standard diesel engine, valued for its reliability and fuel economy in
long-distance touring applications.
Volkswagen Transporter Syncro (T4): The all-wheel-drive Syncro variants utilized
the AAB in conjunction with a transfer case and rear differential. The engine’s
torque output at low engine speeds complemented the off-road capability of the
Syncro system.
Volkswagen LT (early applications): A limited number of Volkswagen LT light
trucks received the AAB engine during the transition period before the
introduction of the dedicated LT diesel engines.
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