1998 AUDI A8 engine

15-29

Compression, checking


Test conditions

Engine oil temperature at least 30 C

Battery fully charged

- Disconnect harness connectors from all 6 fuel
injectors.

- Disconnect 5-pin harness connector from power
output stage of ignition coils.

- Open throttle fully.

- Use VAG1381 or VAG1763 compression tester
to check compression.

- Operate starter until no further pressure
increases are indicated by VAG1381 or
VAG1763 compression tester.

Compression pressure
New
Wear
limit Max. permissable
difference between
cylinders
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15-30

Sealing cap (core plug) in cylinder head,
installing

Cylinder heads supplied as replacement parts
can be used on either the left or right-sides of the
engine. A sealing cap (core plug) must be
installed in the front end of the cylinder head in
each case.

- Coat outside circumference of sealing cap (core
plug) with sealant AMV 188 001 02.

CAUTION!

Part numbers are listed here for reference
only. Always check with your Parts
department for the latest information.

- Using VW295 needle bearing drift, drive in sealing cap (core plug) until
outside rim is flush with end of chamfer in cylinder head (see inset).
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15-31

Camshafts and camshaft adjusters,
removing and installing


Removing

- Remove engine cover (arrows).
Cylinder head installed Lock carrier in service position page 13
-1
- Remove ribbed belt page 13
-8 .
- Remove toothed belt page 13
-12
.

Left-side cylinder head - Remove noise insulation panel (arrows).
- Unbolt engine coolant expansion tank from bracket and lay aside.
- Remove crankshaft housing ventilation line from valve cover.
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15-40

CAUTION!

After installing new hydraulic lifters, the
engine must not be started for approx. 30
minutes. The hydraulic valve lifters have to
settle (otherwise valves will strike the
pistons).
After installing the valvetrain and lifters,
carefully rotate the crankshaft by hand at
least 2 full revolutions before starting to be
sure that valves do not strike the pistons.

Sealing contact surfaces between bearing cap and cylinder head.
- Carefully apply a small amount of sealant D 454 300 A2 at four end
points of sealing surfaces on cylinder head (arrows) using small screw
driver.
- Install cylinder head cover.
- Install toothed belt page 13
-15
.
- Remove ribbed belt page 13
-8 .
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15-45

Hydraulic valve lifters, checking


CAUTION!

After installing new hydraulic valve lifters the
engine must not be started for about 30
minutes. The hydraulic valve lifters must
settle (otherwise valves will strike pistons).
Then turn crankshaft two full revolutions by
hand before starting.

Notes:

Only replace hydraulic valve lifters in complete
sets. Hydraulic valve lifters cannot be adjusted
or repaired.
Irregular valve noise when starting engine is
normal.

- Start engine and let run until coolant
temperature reaches at least 80 C.

- Increase RPM to 2500 for about 2 minutes. If
necessary, test drive vehicle.
If hydraulic valve lifters are still loud, locate faulty
valve lifter as follows:

- Remove cylinder head cover.
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15-52

Valve guides, checking

When servicing engines or cylinder heads with
leaking valves, refacing or replacing valve seats
and valves is not sufficient. Valve guides must be
checked for wear. This is especially important for
engines with high mileage.

Wear limit - Insert valve into guide.
Valve shaft edge must seal with guide. Due to differences in valve stem
diameter, make sure only intake valves are used to check intake
guides, and only exhaust valves are used to check exhaust guides.
- Measure axial play.Intake valve guide
Exhaust valve guide
0.8 mm (0.031 in.) 0.8 mm (0.031 in.) - If wear limit is exceeded, replace cylinder head.
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