Seat BMW 3 SERIES 1988 E30 Workshop Manual

REPAIRS & OVERHAUL
Engine and Associated Systems
In-car engine repair procedures Page 2A•1
General engine overhaul procedures Page2B•1
Cooling, heating and air conditioning systems Page3•1
Fuel and exhaust systems Page 4•1
Engine electrical systems Page5•1
Engine management and emission control systems Page6•1
Transmission
Manual transmission Page7A•1
Automatic transmission Page7B•1
Clutch and driveline Page 8•1
Brakes
Braking systemPage 9•1
Suspension
Suspension and steering systems Page 10•1
Body Equipment
Bodywork and fittings Page 11•1
Electrical
Body electrical systems Page 12•1
Wiring DiagramsPage 12•10
REFERENCE
MOT Test Checks
Checks carried out from the driver’s seat PageREF•1
Checks carried out with the vehicle on the ground PageREF•2
Checks carried out with the vehicle raised PageREF•3
Checks carried out on your vehicle’s exhaust emission system PageREF•4
Tools and Working Facilities Page REF•5
General Repair Procedures Page REF•8
Fault FindingPage REF•9
Conversion factors PageREF•17
Automotive chemicals and lubricants PageREF•18
Buying spare parts and vehicle identification numbers PageREF•19
Glossary of Technical Terms PageREF•20
IndexPage REF•25
Contents

inhibitors wear out, so it must be renewed at
the specified intervals.
Brake and clutch fluid
Warning: Brake fluid can harm
your eyes and damage painted
surfaces, so use extreme caution
when handling or pouring it. Do
not use brake fluid that has been standing
open or is more than one year old. Brake
fluid absorbs moisture from the air, which
can cause a dangerous loss of brake
effectiveness. Use only the specified type
of brake fluid. Mixing different types (such
as DOT 3 or 4 and DOT 5) can cause brake
failure.
14The brake master cylinder is mounted at
the left rear corner of the engine
compartment. The clutch fluid reservoir
(manual transmission models) is mounted on
the right-hand side.
15To check the clutch fluid level, observe
the level through the translucent reservoir.
The level should be at or near the step
moulded into the reservoir. If the level is low,
remove the reservoir cap to add the specified
fluid (see illustration).
16The brake fluid level is checked by looking
through the plastic reservoir mounted on the
master cylinder (see illustration). The fluid
level should be between the MAX and MIN
lines on the reservoir. If the fluid level is low,
first wipe the top of the reservoir and the cap
with a clean rag, to prevent contamination of
the system as the cap is unscrewed. Top-up
with the recommended brake fluid, but do not
overfill.
17While the reservoir cap is off, check the
master cylinder reservoir for contamination. If
rust deposits, dirt particles or water droplets
are present, the system should be drained
and refilled.
18After filling the reservoir to the proper
level, make sure the cap is seated correctly, to
prevent fluid leakage and/or contamination.
19The fluid level in the master cylinder will
drop slightly as the disc brake pads wear.
There is no need to top up to compensate for
this fall provided that the level stays above the
MIN line; the level will rise again when new
pads are fitted. A very low level may indicateworn brake pads. Check for wear (see Sec-
tion 26).
20If the brake fluid level drops consistently,
check the entire system for leaks immediately.
Examine all brake lines, hoses and
connections, along with the calipers, wheel
cylinders and master cylinder (see Sec-
tion 26).
21When checking the fluid level, if you
discover one or both reservoirs empty or
nearly empty, the brake or clutch hydraulic
system should be checked for leaks and bled
(see Chapters 8 and 9).
Windscreen washer fluid
22Fluid for the windscreen washer system is
stored in a plastic reservoir in the engine
compartment (see illustration).
23In milder climates, plain water can be
used in the reservoir, but it should be kept no
more than two-thirds full, to allow for
expansion if the water freezes. In colder
climates, use windscreen washer system
antifreeze, available at any car accessory
shop, to lower the freezing point of the fluid.
This comes in concentrated or pre-mixed
form. If you purchase concentrated antifreeze,
mix the antifreeze with water in accordance
with the manufacturer’s directions on the
container.
Caution: Do not use cooling
system antifreeze - it will damage
the vehicle’s paint.
5 Tyre and tyre pressure
checks
1
1Periodic inspection of the tyres may save
you the inconvenience of being stranded with
a flat tyre. It can also provide you with vital
information regarding possible problems in
the steering and suspension systems before
major damage occurs.
2Tyres are equipped with bands that will
appear when tread depth reaches 1.6 mm, at
which time the tyres can be considered worn
out. This represents the legal minimum tread
depth; most authorities recommend renewing
any tyre on which the tread depth is 2 mm or
less. Tread wear can be monitored with a
simple, inexpensive device known as a tread
depth indicator (see illustration).
3Note any abnormal tyre wear (see
illustration overleaf). Tread pattern irregular-
ities such as cupping, flat spots and more
wear on one side than the other are
indications of front end alignment and/or
wheel balance problems. If any of these
conditions are noted, take the vehicle to a tyre
specialist to correct the problem.
4Look closely for cuts, punctures and
embedded nails or tacks. Sometimes, after a
nail has embedded itself in the tread, a tyre
will hold air pressure for a short time, or may
1•9
4.22 The windscreen washer fluid reservoir
is located in the right front corner of the
engine compartment on most models4.16 The brake fluid level should be kept
above the MIN mark on the translucent
reservoir - unscrew the cap to add fluid4.15 Adding hydraulic fluid to the clutch
fluid reservoir
5.4a If a slow puncture is suspected,
check the valve core first to make sure it’s
tight5.2 Use a tyre tread depth indicator to
monitor tyre wear - they are available at
car accessory shops and service stations,
and cost very little
1
Weekly Checks

5With the engine cool, remove the HT lead
from one spark plug. Do this by grabbing the
connector at the end of the wire, not the lead
itself (see illustration). Sometimes it is
necessary to use a twisting motion while the
connector and HT lead are pulled free.
6If compressed air is available, use it to blow
any dirt or foreign material away from the
spark plug area. A common bicycle pump will
also work. The idea here is to eliminate the
possibility of debris falling into the cylinder as
the spark plug is removed.
7Place the spark plug socket over the plug,
and remove it from the engine by turning it
anti-clockwise (see illustration).
8Compare the spark plug with those shown
in the accompanying photos to get an
indication of the overall running condition of
the engine.
9Apply a little copper-based anti-seize
compound to the threads of the new spark
plug. Locate the plug into the head, screwing
it in with your fingers until it no longer turns,
then tighten it with the socket. If available, use
a torque wrench to tighten the plug to ensure
that it is seated correctly. The correct torque
figure is included in this Chapter’s Specifi-
cations.10Before pushing the HT lead onto the end of
the plug, inspect it as outlined in Section 15.
11Attach the HT lead to the new spark plug,
again using a twisting motion on the
connector until it is firmly seated on the spark
plug.
12Follow the above procedure for the
remaining spark plugs, renewing them one at
a time to prevent mixing up the spark plug HT
leads.
15 Spark plug HT leads,
distributor cap and rotor -
check and renewal
1
1The spark plug HT leads should be checked
at the recommended intervals, and whenever
new spark plugs are fitted in the engine.
2Begin this procedure by making a visual
check of the spark plug HT leads while the
engine is running. In a darkened garage (make
sure there is ventilation) start the engine and
observe each HT lead. Be careful not to come
into contact with any moving engine parts. If
there is a break in the wire, you will see arcing
or a small spark at the damaged area. If arcing
is noticed, make a note to obtain new HT
leads, then allow the engine to cool.
3Disconnect the battery negative cable.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you have
the correct activation code
before disconnecting the battery. Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
4The HT leads should be inspected one at a
time to prevent mixing up the firing order,
which is essential for proper engine operation.
5Disconnect the HT lead from the spark
plug. Do not pull on the lead itself, only on the
connector.
6Inspect inside the connector for corrosion,
which will look like a white crusty powder.
Push the HT lead and connector back onto
the end of the spark plug. It should be a tight
fit on the plug end. If it is not, remove the lead
and use pliers to carefully crimp the metal
terminal inside the connector until it fits
securely on the end of the spark plug.
7Using a clean rag, wipe the entire length of
the HT lead to remove any built-up dirt and
grease. Once the lead is clean, check for
burns, cracks and other damage. Do not bend
the lead excessively, since the conductor
might break.
8Disconnect the HT lead from the distributor.
Again, pull only on the connector. Check for
corrosion and a tight fit in the same manner as
the spark plug end. Renew the HT lead in the
distributor if necessary.
9Check the remaining spark plug HT leads,
making sure they are securely fastened at the
distributor and spark plug when the check is
complete.
10If new spark plug HT leads are required,
purchase a set for your specific engine model.
Lead sets are available pre-cut, with the
connectors already fitted. Remove and renew
the HT leads one at a time, to avoid mix-ups
in the firing order.
11Loosen the screws or detach the clips and
remove the distributor cap (see illustration).
Remove the screws (if applicable) and pull the
rotor off the shaft (see illustration). Check the
distributor cap and rotor for wear. Look for
cracks, carbon tracks and worn, burned or
loose contacts (see illustrations). Renew the
cap and rotor if defects are found. It is
common practice to fit a new cap and rotor
whenever new spark plug HT leads are fitted.
When fitting a new cap, remove the HT leads
from the old cap one at a time, and attach
1•18
15.11b Use an Allen key to remove the
screws, then lift the rotor off the shaft
(later models)15.11a On later models, loosen the screws
and detach the distributor cap up so you
can inspect the inside
14.7 Use a socket spanner with an
extension to unscrew the spark plugs14.5 When removing the spark plug HT
leads, pull only on the connector
Every 12 000 miles
Where there might be difficulty in
inserting the spark plugs into the spark
plug holes, or the possibility of cross-
threading them into the head, a short
piece of rubber or plastic tubing can be
fitted over the end of the spark plug.
The flexible tubing will act as a universal
joint to help align the plug with the plug
hole, and should the plug begin to
cross-thread, the hose will slip on the
spark plug, preventing thread damage.

Torque wrench settings (continued)Nm
Connecting rod cap bolts/nuts
M10 and M30 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
M20 and M40 engines
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Angle-tighten an additional 70°
Camshaft bearing caps (M40 engine) . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Intermediate shaft sprocket-to-shaft bolt (M20 engine) . . . . . . . . . . . . . 60
Oil supply tube bolt(s)
M6 (normal) and M8 (banjo) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
M5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
* BMW recommend that the main bearing bolts are renewed as a matter of course.
2B•4 General engine overhaul procedures
1 General information
Included in this Part of Chapter 2 are the
general overhaul procedures for the cylinder
head and engine internal components.
The information ranges from advice
concerning preparation for an overhaul and
the purchase of new parts to detailed,
paragraph-by-paragraph procedures covering
removal and refitting of internal components
and the inspection of parts.
The following Sections have been written
based on the assumption that the engine has
been removed from the vehicle. For
information concerning in-vehicle engine
repair, as well as removal and refitting of the
external components necessary for the
overhaul, see Chapter 2A, and Section 7 of
this Part.
The Specifications included in this Part are
only those necessary for the inspection and
overhaul procedures which follow. Refer to
Part A for additional Specifications.
2 Engine overhaul-
general information
It’s not always easy to determine when, or
if, an engine should be completely
overhauled, as a number of factors must be
considered.
High mileage is not necessarily an
indication that an overhaul is needed, while
low mileage doesn’t preclude the need for an
overhaul. Frequency of servicing is probably
the most important consideration. An engine
that’s had regular and frequent oil and filter
changes, as well as other required
maintenance, will most likely give many
thousands of miles of reliable service.
Conversely, a neglected engine may require
an overhaul very early in its life.
Excessive oil consumption is an indication
that piston rings, valve seals and/or valve
guides are in need of attention. Make sure
that oil leaks aren’t responsible before
deciding that the rings and/or guides are
worn. Perform a cylinder compression check
to determine the extent of the work required
(see Section 3).Check the oil pressure: Unscrew the oil
pressure sender unit, and connect an oil
pressure gauge in its place. Measure the oil
pressure with the engine at its normal
operating temperature. Compare your
readings to the oil pressures listed in this
Chapter’s Specifications. If the readings are
significantly below these (and if the oil and oil
filter are in good condition), the crankshaft
bearings and/or the oil pump are probably
worn out. On M10 and M30 engines, the oil
pressure sender unit is located high on the left
rear of the cylinder head. On M20 engines, the
sender unit is threaded into the side of the
engine block, below the oil filter. On M40
engines, the sender unit is threaded into the
rear of the oil filter housing.
Loss of power, rough running, knocking or
metallic engine noises, excessive valve train
noise and high fuel consumption may also
point to the need for an overhaul, especially if
they’re all present at the same time. If a
complete tune-up doesn’t remedy the
situation, major mechanical work is the only
solution.
An engine overhaul involves restoring the
internal parts to the specifications of a new
engine. During an overhaul, new piston rings
are fitted and the cylinder walls are
reconditioned (rebored and/or honed). If a
rebore is done by an engineering works, new
oversize pistons will also be fitted. The main
bearings and connecting big-end bearings are
generally renewed and, if necessary, the
crankshaft may be reground to restore the
journals. Generally, the valves are serviced as
well, since they’re usually in less-than-perfect
condition at this point. While the engine is
being overhauled, other components, such as
the distributor, starter and alternator, can be
rebuilt as well. The end result should be a like-
new engine that will give many thousands of
trouble-free miles. Note: Critical cooling
system components such as the hoses,
drivebelts, thermostat and water pump MUST
be renewed when an engine is overhauled.
The radiator should be checked carefully, to
ensure that it isn’t clogged or leaking (see
Chapters 1 or 3). Also, we don’t recommend
overhauling the oil pump - always fit a new
one when an engine is rebuilt.
Before beginning the engine overhaul, read
through the entire procedure to familiarise
yourself with the scope and requirements ofthe job. Overhauling an engine isn’t difficult if
you follow all of the instructions carefully,
have the necessary tools and equipment and
pay close attention to all specifications;
however, it is time consuming. Plan on the
vehicle being tied up for a minimum of two
weeks, especially if parts must be taken to an
automotive machine shop for repair or recon-
ditioning. Check on availability of parts and
make sure that any necessary special tools
and equipment are obtained in advance. Most
work can be done with typical hand tools,
although a number of precision measuring
tools are required for inspecting parts to
determine if they must be replaced. Often an
automotive machine shop will handle the
inspection of parts and offer advice
concerning reconditioning and renewal. Note:
Always wait until the engine has been
completely disassembled and all components,
especially the engine block, have been
inspected before deciding what service and
repair operations must be performed by an
automotive machine shop. Since the block’s
condition will be the major factor to consider
when determining whether to overhaul the
original engine or buy a rebuilt one, never
purchase parts or have machine work done on
other components until the block has been
thoroughly inspected. As a general rule, time
is the primary cost of an overhaul, so it doesn’t
pay to refit worn or substandard parts.
As a final note, to ensure maximum life and
minimum trouble from a rebuilt engine,
everything must be assembled with care, in a
spotlessly-clean environment.
3 Compression check
2
1A compression check will tell you what
mechanical condition the upper end (pistons,
rings, valves, head gaskets) of your engine is
in. Specifically, it can tell you if the
compression is down due to leakage caused
by worn piston rings, defective valves and
seats, or a blown head gasket. Note:The
engine must be at normal operating
temperature, and the battery must be fully-
charged, for this check.
2Begin by cleaning the area around the
spark plugs before you remove them
(compressed air should be used, if available,

otherwise a small brush or even a bicycle tyre
pump will work). The idea is to prevent dirt
from getting into the cylinders as the
compression check is being done.
3Remove all the spark plugs from the engine
(see Chapter 1).
4Block the throttle wide open, or have an
assistant hold the throttle pedal down.
5On carburettor models, disconnect the LT
lead from the coil. On fuel injection models,
disable the fuel pump and ignition circuit by
removing the main relay(see illustration).
This is to avoid the possibility of a fire from
fuel being sprayed in the engine
compartment. The location of the main relay is
generally near the fuse panel area under the
bonnet, but refer to Chapter 12 for the
specific location on your model.
6Fit the compression gauge in the No 1
spark plug hole (No 1 cylinder is nearest the
radiator).
7Turn the engine on the starter motor over at
least seven compression strokes, and watch
the gauge. The compression should build up
quickly in a healthy engine. Low compression
on the first stroke, followed by gradually-
increasing pressure on successive strokes,
indicates worn piston rings. A low
compression reading on the first stroke, which
doesn’t build up during successive strokes,
indicates leaking valves or a blown head
gasket (a cracked head could also be the
cause). Deposits on the undersides of the
valve heads can also cause low compression.
Record the highest gauge reading obtained.
8Repeat the procedure for the remaining
cylinders, and compare the results to the
compression listed in this Chapter’s Specifi-
cations.
9If compression was low, add some engine
oil (about three squirts from a plunger-type oil
can) to each cylinder, through the spark plug
hole, and repeat the test.
10If the compression increases after the oil
is added, the piston rings are definitely worn.
If the compression doesn’t increasesignificantly, the leakage is occurring at the
valves or head gasket. Leakage past the
valves may be caused by burned valve seats
and/or faces or warped, cracked or bent
valves.
11If two adjacent cylinders have equally low
compression, there’s a strong possibility that
the head gasket between them is blown. The
appearance of coolant in the combustion
chambers or the crankcase would verify this
condition.
12If one cylinder is 20 percent lower than the
others, and the engine has a slightly rough
idle, a worn exhaust lobe on the camshaft
could be the cause.
13If the compression is unusually high, the
combustion chambers are probably coated
with carbon deposits. If that’s the case, the
cylinder head should be removed and
decarbonised.
14If compression is way down, or varies
greatly between cylinders, it would be a good
idea to have a leak-down test performed by a
garage. This test will pinpoint exactly
where the leakage is occurring and how
severe it is.
4 Engine removal-
methods and precautions
If you’ve decided that an engine must be
removed for overhaul or major repair work,
several preliminary steps should be taken.
Locating a suitable place to work is
extremely important. Adequate work space,
along with storage space for the vehicle, will
be needed. If a workshop or garage isn’t
available, at the very least a flat, level, clean
work surface made of concrete or asphalt is
required.
Cleaning the engine compartment and
engine before beginning the removal
procedure will help keep tools clean and
organised.
An engine hoist or A-frame will also be
necessary. Make sure the equipment is rated
in excess of the combined weight of the
engine and accessories. Safety is of primary
importance, considering the potential hazards
involved in lifting the engine out of the vehicle.
If the engine is being removed by a novice,
a helper should be available. Advice and aid
from someone more experienced would also
be helpful. There are many instances when
one person cannot simultaneously perform all
of the operations required when lifting the
engine out of the vehicle.
Plan the operation ahead of time. Arrange
for or obtain all the tools and equipment you’ll
need prior to beginning the job. Some of the
equipment necessary to perform engine
removal and refitting safely and with relative
ease are (in addition to an engine hoist) a
heavy-duty trolley jack, complete sets of
spanners and sockets as described in thefront of this manual, wooden blocks, and
plenty of rags and cleaning solvent for
mopping up spilled oil, coolant and fuel. If the
hoist must be hired, make sure that you
arrange for it in advance, and perform all of
the operations possible without it beforehand.
This will save you money and time.
Plan for the vehicle to be out of use for
quite a while. A machine shop will be required
to perform some of the work which the do-it-
yourselfer can’t accomplish without special
equipment. These establishments often have
a busy schedule, so it would be a good idea
to consult them before removing the engine,
in order to accurately estimate the amount of
time required to rebuild or repair components
that may need work.
Always be extremely careful when removing
and refitting the engine. Serious injury can
result from careless actions. Plan ahead, take
your time and a job of this nature, although
major, can be accomplished successfully.
Warning: The air conditioning
system is under high pressure.
Do not loosen any fittings or
remove any components until
after the system has been discharged by a
qualified engineer. Always wear eye
protection when disconnecting air
conditioning system fittings.
Caution: If removing the M40
engine, it is important not to turn
the engine upside-down for
longer than 10 minutes since it is
possible for the oil to drain out of the
hydraulic tappets. This would render the
tappets unserviceable, and damage could
possibly occur to the engine when it is
next started up.
5 Engine- removal and refitting
3
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code before
disconnecting the battery.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
Removal1Relieve the fuel system pressure (see
Chapter 4), then disconnect the negative
cable from the battery.
2Cover the wings and front panel, and
remove the bonnet (see Chapter 11). Special
pads are available to protect the wings, but an
old bedspread or blanket will also work.
3Remove the air cleaner housing and intake
ducts (see Chapter 4).
4Drain the cooling system (see Chapter 1).
5Label the vacuum lines, emissions system
hoses, wiring connectors, earth straps and
fuel lines, to ensure correct refitting, then
General engine overhaul procedures 2B•5
3.5 As a safety precaution, before
performing a compression check, remove
the cover and the main relay (arrowed)
from the left side of the engine
compartment to disable the fuel and
ignition systems (525i model shown, other
models similar)
2B

rocker shafts with a threaded front hole,
screw in a slide hammer to pull the shaft from
the head.
14As each rocker arm shaft is slid out of the
cylinder head, the rocker arms will be
released, one by one.
15Drop each rocker arm into a labelled bag,
so they can be returned to their original
locations on reassembly. While you’re
removing the rocker arm shafts, note their
orientation. The guide plate notches and the
small oil holes face in; the large oil holes face
down, toward the valve guides. Also, label the
rocker shafts so they can be returned to their
original locations in the cylinder head.
M40 engines
Caution: Keep the cylinder head
upright until all of the hydraulic
tappets have been removed. If
this precaution is not taken, the
oil may drain out of the tappets and render
them unserviceable.
16Check that the camshaft bearing caps are
numbered or identified for location.
17Progressively unscrew and remove the
camshaft bearing cap retaining bolts, then
remove the caps (see illustrations).
18Lift the camshaft from the top of the
cylinder head, and remove the oil seal from
the timing end.
19Have ready a compartmentalised box
filled with engine oil to receive the hydraulic
tappets so that they are kept identified for
their correct location (see illustration). Also
have a further box ready to receive the cam
followers.20Remove the cam followers and thrust
discs, then lift out the hydraulic tappets from
their bores in the cylinder head (see
illustrations).
All engines
21Before the valves are removed, arrange to
label and store them, along with their related
components, so they can be kept separate
and reinstalled in the same valve guides from
which they’re removed (see illustration).
22Compress the springs on the first valve
with a spring compressor, and remove the
collets (see illustration). Carefully release the
valve spring compressor, and remove the
retainer, the spring and the spring seat (if
used).
23Pull the valve out of the head, then
remove the oil seal from the guide.
General engine overhaul procedures 2B•9
8.19 Compartmentalised box to hold the
hydraulic tappets (M40 engine)8.17b . . . and camshaft - M40 engine8.17a Removing the camshaft bearing
caps . . .
8.22 Using a valve spring compressor to
compress a valve spring
8.21 A small plastic bag, with an
appropriate label, can be used to store the
valve components so they can be kept
together and refitted in the original position
8.20b . . . and thrust discs . . .8.20a Remove the cam followers . . .
8.20c . . . then lift out the hydraulic tappets
2B
If the valve binds in the guide (won’t
pull through), push it back into the
head, and deburr the area around the
collet groove with a fine file or
whetstone.

24Repeat the procedure for the remaining
valves. Remember to keep all the parts for
each valve together, so they can be refitted in
the same locations.
25Once the valves and related components
have been removed and stored in an
organised manner, the head should be
thoroughly cleaned and inspected. If a
complete engine overhaul is being done,
finish the engine dismantling procedures
before beginning the cylinder head cleaning
and inspection process.
9 Cylinder head and
components-
cleaning and inspection
4
1Thorough cleaning of the cylinder head(s)
and related valve train components, followed
by a detailed inspection, will enable you to
decide how much valve service work must be
done during the engine overhaul. Note: If the
engine was severely overheated, the cylinder
head is probably warped (see paragraph 10).
Cleaning
2Scrape all traces of old gasket material and
sealing compound off the cylinder head,
intake manifold and exhaust manifold sealing
surfaces. Be very careful not to gouge the
cylinder head. Special gasket removal
solvents are available at motor factors.
3Remove all built-up scale from the coolant
passages.
4Run a stiff brush through the various holes
to remove deposits that may have formed in
them.
5Run an appropriate-size tap into each of the
threaded holes, to remove corrosion and
thread sealant that may be present. If
compressed air is available, use it to clear the
holes of debris produced by this operation.
Warning: Wear eye protection
when using compressed air!
6Clean the cylinder head with solvent, and
dry it thoroughly. Compressed air will speed
the drying process, and ensure that all holesand recessed areas are clean. Note:
Decarbonising chemicals are available, and
may prove very useful when cleaning cylinder
heads and valve train components. They are
very caustic, however, and should be used
with caution. Be sure to follow the instructions
on the container.
7Clean all the rocker shafts/arms/followers,
springs, valve springs, spring seats, keepers
and retainers with solvent, and dry them
thoroughly. Clean the components from one
valve at a time, to avoid mixing up the parts.
Caution: DO NOT clean the
hydraulic tappets of the M40
engine; leave them completely
immersed in oil.
8Scrape off any heavy deposits that may
have formed on the valves, then use a
motorised wire brush to remove deposits from
the valve heads and stems. Again, make sure
the valves don’t get mixed up.
Inspection
Note: Be sure to perform all of the following
inspection procedures before concluding that
machine shop work is required. Make a list of
the items that need attention.
Cylinder head
9Inspect the head very carefully for cracks,
evidence of coolant leakage, and other
damage. If cracks are found, check with an
machine shop concerning repair. If repair isn’t
possible, a new cylinder head should be
obtained.
10Using a straightedge and feeler gauge,
check the head gasket mating surface for
warpage (see illustration). If the warpage
exceeds the limit listed in this Chapter’s
Specifications, it may be possible to have it
resurfaced at a machine shop, providing the
head is not reduced to less than the specified
minimum thickness.
11Examine the valve seats in each of the
combustion chambers. If they’re badly pitted,
cracked or burned, the head will require
servicing that’s beyond the scope of the home
mechanic.12Check the valve stem-to-guide clearance
by measuring the lateral movement of the
valve stem with a dial indicator (see
illustration). The valve must be in the guide
and approximately 2.0 mm off the seat. The
total valve stem movement indicated by the
gauge needle must be divided by two, to
obtain the actual clearance. After this is done,
if there’s still some doubt regarding the
condition of the valve guides, they should be
checked by a machine shop (the cost should
be minimal).
Valves
13Carefully inspect each valve face for
uneven wear, deformation, cracks, pits and
burned areas (see illustration). Check the
valve stem for scuffing and the neck for
cracks. Rotate the valve, and check for any
obvious indication that it’s bent. Look for pits
and excessive wear on the end of the stem.
The presence of any of these conditions
indicates the need for valve service as
described in the next Section.
14Measure the margin width on each valve
(see illustration). Any valve with a margin
narrower than specified will have to be
replaced with a new one.
Valve components
15Check each valve spring for wear on the
ends. The tension of all springs should be
checked with a special fixture before deciding
2B•10 General engine overhaul procedures
9.14 The margin width on each valve must
be as specified (if no margin exists, the
valve cannot be reused)
9.13 Check for valve wear at the points
shown here
9.12 A dial indicator can be used to
determine the valve stem-to-guide
clearance (move the valve as indicated by
the arrows)
9.10 Check the cylinder head gasket
surface for warpage by trying to slip a
feeler gauge under the straightedge (see
this Chapter’s Specifications for the
maximum warpage allowed, and use a
feeler gauge of that thickness)
1 Valve tip
2 Collet groove
3 Stem (least-worn
area)4 Stem (most-worn
area)
5 Valve face
6 Margin

that they’re suitable for use in a rebuilt engine
(take the springs to a machine shop for this
check).
16Stand each spring on a flat surface, and
check it for squareness (see illustration). If
any of the springs are distorted or sagged, or
possibly have a broken coil, fit new parts.
17Check the spring retainers and keepers
for obvious wear and cracks. Any
questionable parts should be renewed, as
extensive damage will occur if they fail during
engine operation.
Rocker arms (M10, M20 and
M30 engines)
Note:The rocker arms for the exhaust valves
are the most subject to wear, and should be
checked with particular care.
18Inspect all the rocker arms for excessive
wear on the tips that contact the valve stem
and camshaft (see illustration).
19Check the rocker arm radial clearance
(see Section 8). If it’s excessive, either the
rocker arm bush or the shaft (or both) is
excessively worn. To determine which is more
worn, slide the rocker arm onto an unworn
portion of the rocker arm shaft, and check the
radial clearance again. If it’s now within speci-
fications, the shaft is probably the most-worn
component. If it’s not within specifications,
the rocker arm bushes should be renewed.
Rocker arm shafts (M10, M20 and
M30 engines)
20Check the shafts for scoring, excessive
wear and other damage. The areas where therocker arms contact the shafts should be
smooth. If there is a visible ridge at the edge
of where the rocker arm rides, the shaft is
probably worn excessively.
Cam followers and hydraulic tappets
(M40 engines)
21Check the cam followers where they
contact the valve stems and pivot posts for
wear, scoring and pitting. If there is excessive
wear on both the followers and camshaft,
then a new camshaft, complete with cam
followers, must be obtained.
22Similarly check the hydraulic tappets where
they contact the bores in the cylinder head for
wear, scoring and pitting. Occasionally, a
hydraulic tappet may be noisy and require
renewal, and this will have been noticed when
the engine was running. It is not easy to check a
tappet for internal damage or wear once it has
been removed; if there is any doubt, a complete
set of new tappets should be fitted.
Camshaft
23Inspect the camshaft journals (the round
bearing areas) and lobes for scoring, pitting,
flaking and excessive wear. Using a
micrometer, measure the height of each
exhaust and intake lobe. Compare the heights
of all the exhaust lobes and intake lobes. If the
readings among the exhaust valve lobes or
intake valve lobes vary more than about
0.08 mm, or if the camshaft is exhibiting any
signs of wear, renew the camshaft.
24Inspect the camshaft bearing surfaces in
the cylinder head for scoring and other
damage. If the bearing surfaces are scored or
damaged, you’ll normally have to renew the
cylinder head, since the bearings are simply a
machined surface in the cylinder head. Note:
A machine shop (particularly one that
specialises in BMWs) or dealer service
department may be able to provide an
alternative to fitting a new cylinder head, if the
only problem with the head is mildly-scored
camshaft bearing surfaces.
25Using a micrometer, measure the journals
on the camshaft, and record the
measurements (see illustration). Using a
telescoping gauge or inside micrometer,measure the camshaft bearing diameters in the
cylinder head (on the M40 engine, refit the
bearing caps first). Subtract the camshaft
journal measurement from its corresponding
bearing inside diameter to obtain the oil
clearance. Compare the oil clearance to what’s
listed in this Chapter’s Specifications. If it’s not
within tolerance, a new camshaft and/or
cylinder head will be required. Note:Before
fitting a new cylinder head, check with a
machine shop (particularly one that specialises
in BMWs). They may be able to repair the head.
10 Valves- servicing
4
1Examine the valves as described in Sec-
tion 9, paragraphs 13 and 14. Renew any
valve that shows signs of wear or damage.
2If the valve appears satisfactory at this
stage, measure the valve stem diameter at
several points using a micrometer (see
illustration 9.13). Any significant difference in
the readings obtained indicates wear of the
valve stem. Should any of these conditions be
apparent, the valve(s) must be renewed.
3If the valves are in satisfactory condition they
should be ground (lapped) into their respective
seats to ensure a gas-tight seal. If the seat is
only lightly pitted, or if it has been re-cut, fine
grinding compound should be used to produce
the required finish. Coarse valve-grinding
compound should not normally be used,
unless a seat is badly burned or deeply pitted.
If this is the case, the cylinder head and valves
should be inspected by an expert, to decide
whether seat re-cutting or even the renewal of
the valve or seat insert is required.
4Valve grinding is carried out as follows.
Place the cylinder head upside-down on a
bench, with a block of wood at each end to
give clearance for the valve stems.
5Smear a trace of the appropriate grade of
valve-grinding compound on the seat face,
and press a suction grinding tool onto the
valve head. With a semi-rotary action, grind
the valve head to its seat, lifting the valve
occasionally to redistribute the grinding
compound (see illustration).
General engine overhaul procedures 2B•11
9.25 Measure each camshaft bearing
journal and its corresponding bearing
diameter in the cylinder head, then subtract
the journal diameter from the bearing
inside diameter to obtain the oil clearance9.18 Look for signs of pitting, discoloration
or excessive wear on the ends of the
rocker arms where they contact the
camshaft and the valve stem tip10.5 Grinding-in a valve - do not grind-in
the valves any more than absolutely
necessary, or their seats will be
prematurely sunk into the cylinder head
2B
9.16 Check each valve spring for
squareness

6If coarse grinding compound is being used,
work only until a dull, matt even surface is
produced on both the valve seat and the
valve, then wipe off the used compound and
repeat the process with fine compound. When
a smooth, unbroken ring of light grey matt
finish is produced on both the valve and seat,
the grinding operation is complete. Do not
grind in the valves any further than absolutely
necessary.
7When all the valves have been ground-in,
carefully wash off all traces of grinding
compound using paraffin or a suitable solvent
before reassembly of the cylinder head.
11 Cylinder head- reassembly
5
1Make sure the cylinder head is spotlessly-
clean before beginning reassembly.
2If the head was sent out for valve servicing,
the valves and related components will
already be in place. Begin the reassembly
procedure with paragraph 8.
3Starting at one end of the head, applymolybdenum disulphide (“moly”) grease or
clean engine oil to each valve stem, and refit
the first valve.
4Lubricate the lip of the valve guide seal,
carefully slide it over the tip of the valve, then
slide it all the way down the stem to the guide.
Using a hammer and a deep socket or seal-
fitting tool, gently tap the seal into place until
it’s completely seated on the guide (see
illustrations). Don’t twist or distort a seal
during fitting, or it won’t seal properly against
the valve stem. Note:On some engines, the
seals for intake and exhaust valves are
different - don’t mix them up.
5Drop the spring seat or shim(s) over the
valve guide, and set the valve spring and
retainer in place.
6Compress the spring with a valve spring
compressor and carefully refit the collets in
the upper groove, then slowly release the
compressor and make sure the collets seat
properly (see illustration).
7Repeat paragraphs 3 to 6 for each of the
valves. Be sure to return the components to
their original locations - don’t mix them up!
M10, M20 and M30 engines
8Refit the rocker arms and shafts by
reversing the dismantling sequence. Be sure
to refit the rocker shafts in the correct
orientation. The guide plate notches and the
small oil holes face inwards; the large oil holes
face down, toward the valve guides.
9Lubricate the camshaft journals and lobes(see illustration), then carefully insert it into
the cylinder head, rotating it as you go so the
camshaft lobes will clear the rocker arms. It
will also be necessary to compress the rocker
arms against the valve springs, as described
in Section 8, so they’ll clear the camshaft
lobes. Be very careful not to scratch or gouge
the camshaft bearing surfaces in the cylinder
head.
M40 engines
10Lubricate the bores for the hydraulic
tappets in the cylinder head, then insert the
tappets in their original positions.
11Locate the thrust discs and cam followers
on the valves and pivot posts in their original
positions.
12Lubricate the bearing surfaces of the
camshaft in the cylinder head.
13Locate the camshaft in the cylinder head
so that the valves of No 1 cylinder are both
open, and the valves of No 4 cylinder are
“rocking” (exhaust closing and inlet opening).
No 1 cylinder is at the timing belt end.
14Lubricate the bearing surfaces in the
bearing caps, then locate them in their correct
positions and insert the retaining bolts.
Progressively tighten the bolts to the specified
torque.
15Fit a new oil seal to the camshaft front
bearing cap (see Chapter 2A, Section 11).
All engines
16Refit the oil supply tube to the top of the
cylinder head together with new seals, then
tighten the bolts to the specified torque.
17The cylinder head may now be refitted
(see Chapter 2A).
12 Pistons/connecting rods-
removal
5
Note:Before removing the piston/connecting
rod assemblies, remove the cylinder head and
the sump. On M10, M20 and M30 engines
only, remove the oil pump. Refer to the
appropriate Sections in Chapter 2A.
1Use your fingernail to feel if a ridge has
formed at the upper limit of ring travel (about
6 mm down from the top of each cylinder). If
2B•12 General engine overhaul procedures
11.9 Lubricate the camshaft bearing
journals and lobes with engine assembly
paste or molybdenum disulphide (“moly”)
grease
11.6 With the retainer fitted, compress the
valve spring and refit the collets as shown 11.4b . . .then lightly drive on the seal with
a socket or piece of tubing11.4a Lubricate the valve guide seal, and
place it on the guide (the valve should be
in place too) . . .
A light spring placed under
the valve head will greatly
ease the valve grinding
operation.
Apply a small dab of grease to each
collet to hold it in place, if necessary.

5Gently tap the caps with a soft-faced
hammer, then separate them from the engine
block. If necessary, use the bolts as levers to
remove the caps. Try not to drop the bearing
shells if they come out with the caps.
6Carefully lift the crankshaft out of the
engine. It may be a good idea to have an
assistant available, since the crankshaft is
quite heavy (see illustration). With the
bearing shells in place in the engine block and
main bearing caps, return the caps to their
respective locations on the engine block, and
tighten the bolts finger-tight.
14 Intermediate shaft-
removal and inspection
5
Note:The intermediate shaft is used on the
M20 engine only. The shaft rotates in the
engine block parallel to the crankshaft. It is
driven by the timing belt, and its only purpose
is to drive the oil pump.
1Remove the timing belt (see Chapter 2A).
2With the belt removed, unbolt the gear from
the intermediate shaft and unbolt the front
cover.
3Remove the oil pump driveshaft (see
Chapter 2A).
4The shaft is held in the cylinder block by a
retaining plate with two bolts. Remove the
bolts, and pull the shaft forwards and out of
the block.
5Look for any signs of abnormal wear on the
bearing surfaces or the gear at the back end
of the shaft, which drives the oil pump shaft. If
the bearing surfaces in the engine block show
wear, they’ll have to be attended to by a
machine shop.
15 Engine block- cleaning
2
Caution: The core plugs may be
difficult or impossible to retrieve
if they’re driven into the block
coolant passages.
1Remove the core plugs from the engine
block. To do this, knock one side of each plug
into the block with a hammer and punch,
grasp the other side by its edge with large
pliers, and pull it out.
2Using a gasket scraper, remove all traces of
gasket material from the engine block. Be very
careful not to nick or gouge the gasket sealing
surfaces.
3Remove the main bearing caps, and
separate the bearing shells from the caps and
the engine block. Tag the bearings, indicating
which cylinder they were removed from and
whether they were in the cap or the block,
then set them aside.
4Remove all of the threaded oil gallery plugs
from the block. The plugs are usually very
tight - they may have to be drilled out and theholes retapped. Use new plugs when the
engine is reassembled.
5If the engine is extremely dirty, it should be
taken to a machine shop to be steam-
cleaned.
6After the block is returned, clean all oil
holes and oil galleries one more time. Brushes
specifically designed for this purpose are
available at most motor factors. Flush the
passages with warm water until the water runs
clear, dry the block thoroughly, and wipe all
machined surfaces with a light, rust-
preventive oil. If you have access to
compressed air, use it to speed the drying
process and to blow out all the oil holes and
galleries.
Warning: Wear eye protection
when using compressed air!
7If the block isn’t extremely dirty or sludged
up, you can do an adequate cleaning job with
hot soapy water and a stiff brush. Take plenty
of time, and do a thorough job. Regardless of
the cleaning method used, be sure to clean all
oil holes and galleries very thoroughly, dry the
block completely, and coat all machined
surfaces with light oil.
8The threaded holes in the block must be
clean to ensure accurate torque readingsduring reassembly. Run the proper-size tap
into each of the holes to remove rust,
corrosion, thread sealant or sludge, and to
restore damaged threads (see illustration). If
possible, use compressed air to clear the
holes of debris produced by this operation. Be
sure also that the holes are dry- any oil or
other fluid present could cause the block to
be cracked by hydraulic pressure when the
bolts are tightened. Now is a good time to
clean the threads on all bolts. Note that BMW
recommend that the cylinder head bolts and
main bearing bolts are renewed as a matter of
course.
9Refit the main bearing caps, and tighten the
bolts finger-tight.
10After coating the sealing surfaces of the
new core plugs with a suitable sealant, refit
them in the engine block (see illustration).
Make sure they’re driven in straight and
seated properly, or leakage could result.
Special tools are available for this purpose,
but a large socket, with an outside diameter
that will just slip into the core plug, a 1/2-inch
drive extension, and a hammer, will work just
as well.
11Apply non-hardening sealant to the new
oil gallery plugs, and thread them into the
holes in the block. Make sure they’re
tightened securely.
12If the engine isn’t going to be
reassembled right away, cover it with a large
plastic bag to keep it clean.
2B•14 General engine overhaul procedures
15.10 A large socket on an extension can
be used to drive the new core plugs into
the block
15.8 All bolt holes in the block -
particularly the main bearing cap and head
bolt holes - should be cleaned and
restored with a tap (be sure to remove
debris from the holes after this is done)
13.6 Remove the crankshaft by lifting
straight up. Be very careful when removing
the crankshaft - it is very heavy13.4 Use a centre-punch or number-
stamping dies to mark the main bearing
caps to ensure refitting in their original
locations on the block (make the punch
marks near one of the bolt heads)