1998 BMW 525i maintenance

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This group covers cylinder head and valvetrain service and
repair. Some of the repair procedures described here require
that the cylinder head first be removed as described in
113
Cylinder Head Removal and Installation.
NOTE- For timing chain and
VANOS repair information, see 117
Camshaft Timing Chain.
If it is
determined that the cylinder head will require signif-
icant reconditioning work, a remanufactured cylinder head
may be a good alternative. Remanufactured cylinder
heads are available from an authorized
BMW dealer.
The information given in this repair group is organized ac-
cording to engine code. For engine application information,
see
I00 Engine-General.
For specific repair procedures, refer to the appropriate repair
group:
* 020 Maintenance
100 Engine-General
113 Cylinder Head Removal and Installation
117 Camshafi Timing Chain
= 170 Radiator and Coo!ing System
Special Tools
Special BMW tools are required for most cylinder head ser-
vice described in this repair group. Many of these tools are ex-
pensive and only available through an authorized
BMW
dealer. If the special tools are not available, have the cylinder
head removed and disassembled by an authorized BMW
dealer. Be sure to read each procedure thoroughly before
starting a job to determine which special tools and equipment
will be necessary.
Most of the repairs to a cylinder head require precision
rna-
chine work to specific tolerances. This type of work should be
performed by an authorized BMW repairfacility or an ASE
certified machinist.
71 Torque wrench with flex shaft

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Cylinder Head and valvetrain1
Hydraulic lifters, checking and replacing
Self-adjusting hydraulic lifters (A) keep the valve clearances
within a limited working range. Hydraulic lifters are sealed
units and require no maintenance. Section view of camshaft
(6) and valve with conical valve spring (C) shown.
Under some circumstances, such as a cold start, the cam fol-
lowers may emit noise. Hydraulic lifter noise is usually a
high-
pitched tapping or chattering noise. In most instances, this is
considered normal as long as the noise goes away in a few
minutes (maximum
20 minutes). If the noise does not go
away, either the lifter is faulty or the oil pressure to the lifter is
low. Hydraulic lifter replacement requires that the camshaft
first be removed.
NOTE-
Before checking hydraulic lifters, male sure engine oil is
fresh and at the proper level.
Sticky lifters can be the result of
sludge build up in the cylinder head and lifters.
- Run engine until it reaches normal operating temperature.
Shut off engine.
- Working inside luggage compartment, disconnect negative
battery cable.
CAUTION-
Prior to disconnecting battery cable, read the baltery dls-
connection cautions given In 001 General Cautions and
Warnings.
Disconnecting the battery may erase fault
code(s)
stored in control module memory Check for fault codes
4 Remove left and right interior ventilation duct (left side
shown):
Release plastic locking tab
(A) or release loclting tabs on
top of duct (later models).
Rotate duct counterclockwise to
unloclt from bulithead and
remove (arrow).

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1 17-2
Camshaft Timing Chain
This repair group covers timing chain and VANOS repair
information for the following engines:
M52 (Single VANOS 6-cylinder engine)
M52
TU and M54 (Double VANOS engines)
M62 (Non VANOS
V-8 engine)
NOTE-
The M62 TU V-8 engine with VANOS Variable Camshaft
Timing repair information is not included.
NOTE-
See 100 Engine General for engine code and application
information.
Worn timing chains and sprocltets can lead to noisy operation
and erratic valve timing. Afaulty tensionercan also cause tim-
ing chain noises.
For specific repair procedures, refer to the appropriate repair
group:
020 Maintenance
113 Cylinder Head Removal and Installation
119 Lubrication System
121 Ignition System
170 Radiator and Cooling System
Special tools
Special BMW service tools are needed to perform the service
and repairs procedures covered in this repair group. Many of
these tools are expensive and only available through an au-
thorized BMW dealer. Be sure to read each procedure thor-
oughly before starting a job to determine which special tools
will be necessary.
In addition, Double VANOS system diagnosis can only be
carried out by using BMW specific electronic scan tools, such
as BMW
DISplus, MoDiC or equivalent.
4 Torque wrench wl flex extension
(Tool No. BMW 00
9 250)

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Camshaft Timing Chain
4 Crankshaft hub loclting tool. M54 engine
(Tool No.
BMW 11 8 190 11 1 8 200)
4 VANOS test lead, M52 6-cylinder
(Tool No.
BMW 12 6 410)
Crankshaft oil seal, front,
replacing
(M52 engine)
The crankshaft front seal is located in the lower timing cover,
behind the vibration damper.
- Disconnect negative (-) cable from battery.
CAUTIOIG
a Disconnecting the battery may erase fault code(s) stored in
control module memory Check
for fault codes using spe-
cial
BMW diagnostic equipment.
Prior to disconnecting the battery, read
the battery dis-
connection cautions given in
001 General Cautions
and
Warninqs.
- Remove splash guard from beneath engine.
- Remove engine cooling fan assembly. See 170 Radiator
and Cooling System.
NOTE-
Cooling ian nut (32 mm wrench) has left-hand threads.
- Remove drive belts. See 020 Maintenance.
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Camshaft Timing Chain
lnstall vibration damper mounting bolts. Note hub locating
dowel (arrow).
Tightening torque
Vibration damper to crankshaft hub
(ME) 22 Nm (16 ft-lb)
- Installation is reverse of removal noting the following:
Installing drive belts. See 020 Maintenance.
Install cooling fan. See 170 Radiator and Cooling Sys-
tem.
Crankshaft oil seal, replacing
(M52 TU and M54 engines)
The crankshafl front seal IS located in the lower timing cover,
behind the
vibrat~on damper.
- Disconnect negative (-) cable from battery.
Disconnecting the battery may erase fault
code(s) storedin
control module memoy Checlc for fault codes using spe-
cial
BMW diagnostic equipment.
Prior to disconnecting the battery, read the battery dis-
connection cautions given in
001 General Cautions
and Warnings.
- Remove splash guard from beneath engine
- Remove engine cooling fan assembly. See 170 Radiator
and Cooling System.
NOTE- Cooling fan nut
(32 mm wrench) has left-hand threads.
- Remove drive belts. See 020 Maintenance
NOTE-
Mark direction of belt rotation if reusing belt.
- Install crankshaft holding tool (BMW special tool 11 8 19011 1
8 200). Make sure tool locks into place in openings in damper
assembly. While counterholding crankshafl with special tool,
remove crankshaft center bolt.
CAUTIOI\C
Do not use flywheel locling tool to hold crankshaft station-
ary to loosen or tighten
cranl(shaft hub center bolt. Use
only the special tools specified, or equivalent hub holding
tool.
Use care when removing
damper/hub assembly, as ~t is
easy to damage the radiator

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Camshaft Timing chain]
4 Coat new seal with oil and position in timing chain cover. Use
BMW special tool 11
3 280 and crankshaft center bolt to draw
seal in flush with timing case cover.
- Align vibration damper assembly with keyway and tap into
place. Insert new center bolt with washer.
CA
UTIOG
Inspect woodruff key for damage before installing hub
assembly.
- Install crankshaft holding tool malting sure tool locks into
place in openings in damper assembly. While counterholding
cranltshaft, tighten crankshaft center bolt.
- Attach special tools 11 8 20011 1 8 190 to damper assembly.
Counterhold damper with 11 8 190 while tightening center
bolt.
Tightening
torque
Vibration damper hub to crankshaft 410 Nm (302 it-ib)
- Installation is reverse of removal noting the following:
Install drive belts. See 020 Maintenance.
Install cooling fan. See 170 Radiator and Cooling Sys-
tem.
Crankshaft oil seal, replacing
(M62 and M62 TU engines)
- Disconnect negative (-) cable from battery
CAUTIOG
Disconnecting the battery may erase fault code(s) storedin
control module memory. Check for fault codes using spe-
cial BMW diagnostic equipment.
* Prior to disconnecting the battery, read the battery dis-
connection cautions in
001 General cautions and
warnings.
- Remove splash guard from beneath engine
- Remove engine cooling fan assembly. See 170 Radiator
and Cooling System.
NOTE
-
Cooling fan nut (32 mm wrench) has left-hand threads.
- Remove drive belts. See 020 Maintenance.
NOTE-
Marlc direction of belt rotation if reusing belt.

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I Camshaft Timing Chain
Mark 0" location on socket (arrow). Tighten hub bolt in four
stages.
Tightening torque Vibration damper
hub to cranlrshaft
Stage 1 100 Nm (74 it-lb)
Stage
2 60" Torque angle
Stage
3 60" Torque angle
Stage
4 30" Torque angle
- install vibration damper and mounting bolts
NOTE-
Male sure to align vibration damper with locating dowel pin
in hub.
Tightening torque Vibration damper to
cranltshait hub (ME) 22 Nm (16 ft-lb)
- Install drive belts. See 020 Maintenance.
- Install cooling fan. See 170 Radiator and Cooling System.
- Replace under engine splash shield, then reconnect nega-
tive battery cable.
!/ANBS CONTROL UNIT AND
TIMING CHAIN (M52 ENGINE)
VANOS control unit, removing (M52 engine)
NOTE-
Special BMW service tools are required to remove and in-
stall the
VANOS control unit. Read the procedure through
before starting the job.
If the camshafts are notproperly timed, the pistons can
contact the valves.
- Disconnect negative (-) cable from battery.
CAUTION-
Disconnecting the battery may erase fault code(s) stored in
control module memory. Prior to disconnecting the
battev,
check for fault codes using special BMW diagnostic equip-
ment.
* Prior to disconnecting the battery, read the battery dis-
connection cautions given in
001 General Cautions
and Warnings.

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Camshaft Timing Chain Timing chains, removing
(M52 engine)
Camshaft timing chain removal on M52 engines requires en-
gine oil pan removal.
Special
BMW sewice tools are needed for timing chain re-
moval and installation procedures. The special tools assure
propertiming of thevalvetrain. Precise marks to
setthe timing
on the camshafts are not provided for reassembly. Read the
procedures through before beginning the job.
NOTE-
If the camshafts are not properly timed, the pistons can con-
tact the valves.
- Remove VANOS control unit. See VANOS control unit, re-
moving (M52 engine).
- Remove radiator cooling fan and shroud. See 170 Radiator
and Cooling System.
- Drain cooling system. See 170 Radiator and Cooling Sys-
tem.
- Remove coolant hoses from thermostat housing and remove
thermostat housing from front of cylinder head.
- Loosen bolts for coolant pump pulley.
- Remove drive belts for alternator and AIC compressor. See
020 Maintenance.
- Remove coolant pump pulley.
Remove drive belt tensioner mounting bolts (arrows) and re-
move tensioner from front of engine.
- Remove engine speed sensor from lower timing chain cover.