General information about the 2.5 liter diesel engine (Audi A8 D2)

The cars are equipped with liquid-cooled, six-cylinder diesel V-engines. The engines are located longitudinally in the engine compartment.

The engine cylinders are cast from grey cast iron as one piece with the cylinder block. The cylinder heads are made of light alloy and are bolted to the cylinder block. Steel valve guides are pressed into the cylinder head. An oil pan consisting of two sections is attached to the lower part of the engine cylinder block. Oil required for lubrication and cooling of the engine flows into it.

The engines use a cross-flow design, where air enters the engine cylinders on one side and exhaust gases are expelled on the other side of the engine. Injectors deliver fuel directly to the engine cylinders.

Each section of the cylinder block has a separate cylinder head with two camshafts. The intake camshafts are driven by a single toothed belt. The exhaust camshafts are driven by a toothed transmission from the intake camshafts.

Valve clearances are adjusted automatically by hydraulic tappets, so manual adjustment is not required.

An oil pump, driven by a chain from the crankshaft, serves to supply oil to the engine's rubbing surfaces. Under pressure, oil is supplied through channels to the crankshaft and camshaft bearings.

Technical data

Cylinder block
Inner diameter of cylinder, mm:
1st nominal	78,306–78,310
2nd nominal	78,310–78,314
1st enlarged	78,346–78,350
2nd enlarged	78,350–78,354
Pistons
Piston diameter, mm:
1st nominal	78,253–78,261
2nd nominal	78,259–78,267
1st enlarged	78,293–78,301
2nd enlarged	78,299–78,307
Piston rings
Piston ring gap
nominal/maximum permissible, mm:
upper compression	0,20–0,40/ 0,8
lower compression	0,80–1,00/ 1,4
oil scraper	0,25–0,50/ 0,8
Ring clearance in piston groove
nominal/maximum permissible, mm:
upper compression	0,100–0,136/ 0,150
lower compression	0,045–0,085/ 0,110
oil scraper	0,025–0,065/ 0,090
Cylinder head
Deviation from flatness of the mating surface of the cylinder head, mm	0,1
Camshafts
Axial clearance, mm:
nominal	0,06–0,15
maximum permissible	0,3
Radial clearance, mm:
nominal	0,035–0,085
maximum permissible	0,1
Crankshaft
Main journal diameter, mm:
nominal	64,958–64,978
1st repair	64,708–64,728
Diameter of connecting rod journals, mm:
nominal	57,958–57,978
1st repair	57,708–57,728
Axial clearance, mm:
nominal	0,090–0,251
maximum permissible	0,3
Radial clearance, mm:
nominal	0,018–0,045
maximum permissible	0,1

Tightening torques* of main threaded connections, Nm

Coolant drain plug	10
Engine mount to lower frame	25
Drive disk to torque converter	85
Engine torque compensator support to frame	40
Generator to engine:
M8	22
M10	45
Air Conditioning Compressor to Bracket	22
Power steering pump to bracket	22
Pulley to the power steering pump	22
Intake exhaust pipe to turbocharger	25
Vibration damper to crankshaft pulley	22
Tensioner device for the compressor poly V-belt to the bracket	22
Air conditioning compressor poly V-belt tension roller mounting bolt	22
Power steering pump and oil cooler bracket to engine	22
A/C Compressor Bracket to Power Steering Pump and Oil Heat Exchanger Bracket	22
Power steering pump to bracket	22
Pulley to the power steering pump	22
Timing belt pulley to camshaft mounting bolt	75
Bolts for fastening the vibration damper to the fuel pump pulley	22
Viscous coupling radiator fan bracket mounting bolts:
M6	10
M8	22
M10	45
Vacuum pump to cylinder head	10
Fuel pump drive pulley to camshaft pulley mounting bolts	22
Fuel pump timing belt tensioner pulley to viscous coupling radiator fan bracket	36
Flywheel mounting bolt	60 + turn 180°
Vacuum pump mounting bolts	10
Intake Manifold Front Section Mounting Bolts	10
Bolts for fastening the left section of the intake manifold	10
Bolts for fastening the right section of the intake manifold	10
Exhaust Gas Recirculation (EGR) Valve to Intake Manifold	22
Fuel pipes to the fuel pump and injectors	30
Bolts securing the heat shield to the turbocharger	10
Bolts securing the oil line to the intake manifold	22
Cylinder head cover fastening nuts	10
Fuel return pipes to fuel injectors	5
Bolt for fastening the guide pipe for the engine oil level indicator (dipstick) to the head cover	10
Bolts for fastening the oil line to the turbocharger	15
Turbocharger bracket to cylinder block mounting bolts	22
Glow plugs	18
Camshaft bearing cap fastening nuts	15
Cylinder head studs	5
Injectors to the cylinder head	10

* For other threaded connections, the tightening torques are as follows, Nm: M6 – 10; M8 – 20; M10 – 45; M12 – 65.