676_013

14

Piston
To minimize noise, the cast pistons are mounted at a 0.5 mm offset towards the pressure side (see illustration 676_016
below). Due to the compression and valve timing, intake valve recesses of different sizes are integrated in the piston crown
(intake valve: large; exhaust valve: small). The chamber walls on the piston pressure side are narrower than on the counter-pressure side which is subject to less strain. The high rigidity of the pressure side makes it possible to achieve a defined
piston wear pattern while optimizing the load. On the counter-pressure side, the piston is much softer and can adapt better
to the shape of the cylinder. This combination results in different pistons for cylinder bank 1 (right bank) and cylinder bank 2
(left bank).

Piston rings
1. Top piston ring (compression ring) mounted in the ring carrier, rectangular section seal
2. Taper-faced ring
3. Oil scraper ring (3 parts)

Piston pins
The steel alloy piston pins are coated and hardened. Each piston pin measures 22 mm in diameter.

Note

The small valve recesses always face the inner V.

676_014

Piston pressure side
Counter-pressure side

Counter-pressure side
Piston pressure side

676_016

15

Connecting rods
The cracked trapezoidal connecting rods are made of high-strength steel. The bushing in the upper connecting rod small
end is made from a copper alloy (CuNi9Sn6). The connecting rod bearings are 22.3 mm wide. Both bearing shells are
identical. The bearings are made of three materials: a steel substrate, a bismuth-bronze alloy intermediate layer and a thin
bismuth crystal lining. The connecting rods are installed at an offset to the engine’s longitudinal axis.

676_017

Installing the connecting rods
It is important to install the connecting rods in the correct position. The points of the two installation markings must be in
line with one another (see illustration 676_018 ). Only connecting rods of the same weight class may be installed on a
given engine.

Installation marking

View showing data matrix code
XX = weight class of large connecting rod eye
YY = weight class of small connecting rod eye
676_018

676_019

Note

Do not interchange bearing shells during installation; if new components are installed the specifications for
clearance tolerances must be observed (see Elsa Pro for details).
16

Belt pulley / vibration damper
A single bolt secures the pulley/vibration damper to the crankshaft, and a dowel pin locates them in the correct position.
A diamond-coated washer is installed between the vibration damper and the end of the crankshaft as a locating element.
The housing of the viscous vibration damper is made of forged steel, while the inertia ring is manufactured out of
aluminum. This provides the greatest possible strength against deformation caused by centrifugal force.

Diamond-coated friction
washer

Pulley

Crankshaft speed detection

676_020

Engine Speed Sensor G28 is located in the timing chain cover. It detects signals from the magnetic ring on the drive plate.

Magnetic ring
Carrier plate

Engine Speed Sensor
G28
676_021
17

Cylinder head
The cylinder heads have the following technical features:
›
›
›
›
›
›
›
›

DOHC, 4 valves per cylinder.
Roller cam followers.
Integral exhaust manifold.
“Hot Side Inside” (HSI).
Direct injection combustion process with central injector position.
Audi valvelift system (AVS). Enables Cylinder on Demand (CoD) operation.
Intake valves: hardened and tempered.
Exhaust valves: hardened and tempered, sodium-filled hollow stems.

676_023

18

Noise insulation
The two-part insulating mats over the cylinder head covers help reduce noise. This provides effective insulation against
high-frequency ticking noises greater than 2500 Hz from the injectors and the high-pressure fuel pumps.

676_044

Note

Pay close attention to the installation order of components on the cylinder heads. Some components may be
located under the insulating mats and can no longer be installed after the mats have been installed.
19

Cylinder head cover attachments

Camshaft adjuster

Ignition coils

Hall sender

Cylinder head cover
(right-side)

Camshaft control valves
(solenoid)

676 _045

Timing chain case cover

Cylinder head gasket
A three-layer metal gasket is used. It is only available in one thickness.

Cylinder head gasket

676 _024
20

Valve gear

1

10
9
2

8
3

7

6
4
5

676 _025

Legend
1.
2.
3.
4.

Roller cam followers with supporting element
Exhaust valve spring
Twin-lip valve stem oil seal
Exhaust valve
Bi-metal valve with sodium filling and chromium-plated
valve stem ends
5. Inlet valve
Monometallic valves with inductive hardened valve seats
6. Valve spring plate (bottom)
7. Single-lip valve stem oil seal
8. Inlet valve spring
9. Upper valve spring plate
10. Valve keepers

The valve springs are a simple cylindrical shape.

21

Camshaft housings
The camshaft housings of both cylinder banks work in the
same way; the only difference is the location of certain
components. The camshaft housing for cylinder bank 2 is
described here as an example. The cylinder head is sealed
by a liquid gasket and a rubber molded gasket.
The camshafts are mounted in five sleeve bearings in the
camshaft housing. The center bearing is constructed
additionally as an axial bearing. The ignition coils, cam
actuators for Cylinder on Demand, Hall sensors for
camshaft position detection, high pressure fuel pump,
injectors, fuel rail and oil separator for the crankcase
breather system are also installed.
12

11

1
10

2
3
4

7

5
6

8

9
676_026

Legend
1. Cylinder head cover
2. Retention valve
3. Dowel sleeves
4. Seal
5. Camshafts
6. Control valve for camshaft adjuster
7. Axial bearing
8. Bearing cap
9. Bolted connection for camshaft bearing
10. Sealing plug
11. Plug
12. Bolted connection for cylinder head cover

22

Identification number of matched pair for camshaft housing and camshaft bearing

The following applies to the bearing caps:
E for intake side and A for exhaust side; bearing
position number 1 to 5 starting at the front.

676_027

Identification number of matched pair for camshaft housing and cylinder head
The following applies to the camshaft bearing caps:
E for inlet side and A for exhaust side; bearing position
number 1 to 5 starting at the front. The identification
number for the matched pair is given underneath. The
three-digit numbers on the bearing caps (see marking)
must match the last three digits of the four-digit number
on the camshaft housing.
›
›
›

This identification number matches each bearing cap to a
specific cylinder head.
It is important to ensure correct allocation during assembly.
The two four-digit numbers must be the same: XXXX = XXXX.

Camshaft housing

Cylinder head

676_029

23

Camshafts
All four camshafts are composite camshafts comprising a
basic shaft with pressed-on end pieces. The cam elements
are installed onto the splines on the shaft. Two cam elements are fixed in position; the other two are moveable.
The moveable cam elements have two cam profiles for each
valve. This provides the operational basis for the Cylinder
on Demand (CoD) system.

The high-pressure fuel pumps are driven by the exhaust
camshafts via four-lobe cams. In addition, each camshaft
has a sender wheel used for detecting the camshaft position.
The bearings for the camshafts are located in the basic
shaft. A groove for the axial bearing is located in the center
of the camshaft.

676_030

24

Camshaft components
8

7
1

7

6
2

5
3
4

676_031

Legend
1.
2.
3.
4.
5.
6.
7.
8.

Basic shaft
Bearing caps
Ball-and-spring locking mechanism
Control valve for camshaft adjuster
Shaft stub with four-lobe cams for driving the high-pressure fuel pump
Cam elements, moveable for the Cylinder on Demand system
Cam elements
Sender wheel

25

Cylinder on Demand (CoD)
The EA825 engine is equipped with a cylinder management
system. This system allows two cylinders on each cylinder
bank to be shut off in certain circumstances, for example,
under low engine load. When these cylinders are shut off,
the other cylinders can work more effectively with reduced
throttle loss. This saves fuel and reduces exhaust
emissions.
The cylinders are shut off by keeping the corresponding
inlet and exhaust valves closed, and by eliminating the fuel
supply and ignition for these cylinders.

The inlet and exhaust valves are shut off via the Audi
valvelift system. To make this happen, the system’s actuators are activated in the same sequence as the firing order,
which sets the moveable cam elements for cylinder 2, 3, 5
and 8 to zero stroke.
›
›

Firing order with all cylinders activated: 1-3-7-2-6-5-4-8
Firing order with half of cylinders activated: 1-7-6-4

For the vehicle occupants, it will be nearly imperceptible
that only half of the cylinders are activated, as the active
engine mountings eliminate nearly all potential vibrations.
The function of the active engine mountings is described in
SSP 920223 and SSP 990293

Cylinder 1

5/6

1/2

3/4

7/8

Cylinder 2

676_032

Legend
1.
2.
3.
4.
5.
6.
7.
8.

26

Cylinder 2 Exhaust Cam Actuator 1 F454
Cylinder 2 Intake Cam Actuator 1 F452
Cylinder 3 Exhaust Cam Actuator 1 F458
Cylinder 3 Intake Cam Actuator 1 F456
Cylinder 5 Exhaust Cam Actuator 1 F466
Cylinder 5 Intake Cam Actuator 1 F464
Cylinder 8 Exhaust Cam Actuator 1 F478
Cylinder 8 Intake Cam Actuator 1 F476

Cylinder on Demand strategy
Criteria for starting/ending CoD operation

Engine coolant temperature

95°F - 185°F (35°C - 85°C)

Engine torque

Between 62.69 - 162.26 lb ft (85 - 220 Nm) depending on the engine speed

Gear

D

Inactive in gears

1…3

Battery voltage

Greater than 9,6 V

Catalytic converter heating

Inactive

Engine flaps

Inactive

Prevented during OBD diagnosis

› Oxygen sensor check
› Catalytic converter check
› Fuel tank breather check

EVAP system, high load greater than 12

Inactive

Maximum time in CoD cycle

300 s

Exhaust gas is captured and sealed in when the cylinders are shut off.

How the CoD system works
This section describes the three phases in which the sliding cams move from zero to full lift.

Phase 1
When the cam actuator is activated by the engine control
module, the actuator pin is inserted into the Y-shaped
slotted gate. The ball locks the cam element in place
through spring force. The intake and exhaust valves are
closed.

676_033

27

Phase 2
When the camshaft rotates further, the shape of the
slotted gate causes the actuator pin to press the cam
element out of the retainer.

676_034

Phase 3
Once it has changed positions, the cam element is locked in
the second position by the ball through spring force. The
retraction slot pushes the actuator pin back in. This triggers
the retraction signal in the actuator. The intake and exhaust
valves are still closed; they are just about to be opened by
the contour of the full lift cam.

676_035

28

Camshaft adjusters
To optimize power output and torque as well as reducing
emission levels and increasing fuel economy, camshaft
adjusters are installed on all camshafts. The system also
uses an internal exhaust gas recirculation strategy.
The hydraulic camshaft adjusters are in constant operation
and have an adjustment range of 50° (crank angle).

Diamond-coated friction washer,
must not be reused

Camshaft adjuster valve
(solenoid valve, bolted into chain case cover)

Intake camshaft Cylinder bank 2

Timing valve
(also secures camshaft adjuster to camshaft)

Reference

For more information about the camshaft adjuster valve and the control valve, please refer to eSelf-Study
Program 920173, The Audi 3.0L V6 TFSI EA839 Engine.
29

Intake camshaft adjusters
When the engine is switched off, locking pins use spring
force to lock the intake camshaft adjusters in the “retard”
position.

Adjustment range 25° cam angle

Chain sprocket (rotor)

Stator
Locking pin

Direction of camshaft rotation

676_036

Exhaust camshaft adjusters
When the engine is switched off, spring force on the
locking pins locks the exhaust camshaft adjusters in the
“advanced” position. A return spring is necessary to achieve
the “advanced” locking position when switching off the
engine.
Chain sprocket (rotor)

Return spring

Locking pin
Stator

30

676_144

Camshaft drive configuration
The camshaft drive system of the new V8 engine is located
on the transmission side of the engine. A gear on the crankshaft drives the intermediate gear which in turn drives the
simplex chains for the camshafts.
The intermediate gear is configured as a tensioning gear. It
is responsible for preventing noise.

Camshaft Position Sensor 4
G301

Camshaft Position Sensor 3
G300
Tensioning rail

Contact surface

Camshaft Position Sensor 2
G163