Spark plug BMW 3 SERIES 1985 E30 User Guide

1 General information
This Part of Chapter 2 is devoted to in-
vehicle engine repair procedures. All
information concerning engine removal and
refitting and engine block and cylinder head
overhaul can be found in Chapter 2B.
The following repair procedures are based
on the assumption that the engine is still fitted
in the vehicle. If the engine has been removed
from the vehicle and mounted on a stand,
many of the steps outlined in this Part of
Chapter 2 will not apply.
The Specifications included in this Part of
Chapter 2 apply only to the procedures
contained in this Part. Chapter 2B contains
the Specifications necessary for cylinder head
and engine block rebuilding.
The single overhead camshaft four- and
six-cylinder engines covered in this manual
are very similar in design. Where there are
differences, they will be pointed out.
The means by which the overhead
camshaft is driven varies according to engine
type; M10 and M30 engines use a timing
chain, while M20 and M40 engines have a
timing belt.
2 Repair operations possible
with the engine in the vehicle
Many major repair operations can be
accomplished without removing the engine
from the vehicle.
Clean the engine compartment and the
exterior of the engine with some type of
degreaser before any work is done. It will
make the job easier, and help keep dirt out of
the internal areas of the engine.
Depending on the components involved, it
may be helpful to remove the bonnet to
improve access to the engine as repairs are
performed (see Chapter 11 if necessary).
Cover the wings to prevent damage to the
paint. Special pads are available, but an old
bedspread or blanket will also work.
If vacuum, exhaust, oil or coolant leaks
develop, indicating a need for gasket or seal
renewal, the repairs can generally be made
with the engine in the vehicle. The intake and
exhaust manifold gaskets, sump gasket,
crankshaft oil seals and cylinder head gasket
are all accessible with the engine in place.
Exterior components, such as the intake
and exhaust manifolds, the sump, the oil
pump, the water pump, the starter motor, the
alternator, the distributor and the fuel system
components, can be removed for repair with
the engine in place.
The cylinder head can be removed without
removing the engine, so this procedure is
covered in this Part of Chapter 2. Camshaft,
rocker arm and valve component servicing ismost easily accomplished with the cylinder
head removed; these procedures are covered
in Part B of this Chapter. Note, however, that
the camshaft on the M40 engine may be
removed with the engine in the vehicle since it
is retained by bearing caps.
In extreme cases caused by a lack of
necessary equipment, repair or renewal of
piston rings, pistons, connecting rods and
big-end bearings is possible with the engine in
the vehicle. However, this practice is not
recommended, because of the cleaning and
preparation work that must be done to the
components involved.
3 Top Dead Centre (TDC) for
No 1 piston- locating
2
Note 1:The following procedure is based on
the assumption that the distributor (if
applicable) is correctly fitted. If you are trying
to locate TDC to refit the distributor correctly,
piston position must be determined by feeling
for compression at the No 1 spark plug hole,
then aligning the ignition timing marks or
inserting the timing tool in the flywheel, as
applicable.
Note 2:The No 1 cylinder is the one closest to
the radiator.
1Top Dead Centre (TDC) is the highest point
in the cylinder that each piston reaches as it
travels up and down when the crankshaft
turns. Each piston reaches TDC on the
compression stroke and again on the exhaust
stroke, but TDC generally refers to piston
position on the compression stroke.
2Positioning the piston at TDC is an essential
part of many procedures, such as timing belt
or chain removal and distributor removal.
3Before beginning this procedure, be sure to
place the transmission in Neutral, and apply
the handbrake or chock the rear wheels. Also,
disable the ignition system by detaching the
coil wire from the centre terminal of the
distributor cap, and earthing it on the engine
block with a jumper wire. Remove the spark
plugs (see Chapter 1).
4In order to bring any piston to TDC, the
crankshaft must be turned using one of the
methods outlined below. When looking at the
front of the engine, normal crankshaft rotation
is clockwise.
(a) The preferred method is to turn the
crankshaft with a socket and ratchet
attached to the bolt threaded into the
front of the crankshaft.
(b) A remote starter switch, which may save
some time, can also be used. Follow the
instructions included with the switch.
Once the piston is close to TDC, use a
socket and ratchet as described in the
previous paragraph.
(c) If an assistant is available to turn the
ignition switch to the Start position in
short bursts, you can get the piston close
to TDC without a remote starter switch.Make sure your assistant is out of the
vehicle, away from the ignition switch,
then use a socket and ratchet as
described in (a) to complete the
procedure.
5Note the position of the terminal for the
No 1 spark plug lead on the distributor cap. If
the terminal isn’t marked, follow the plug lead
from the No 1 cylinder spark plug to the cap
(No 1 cylinder is nearest the radiator).
6Use a felt-tip pen or chalk to make a mark
directly below the No 1 terminal on the
distributor body or timing cover.
7Detach the distributor cap, and set it aside
(see Chapter 1 if necessary).
8Turn the crankshaft (see paragraph 4
above) until the timing marks (located at the
front of the engine) are aligned (see
illustration). The M40 engine does not have
any timing marks at the front of the engine,
but instead has a timing hole in the flywheel
which must be aligned with a hole in the rear
flange of the cylinder block. On this engine,
turn the crankshaft until the distributor rotor is
approaching the No 1 TDC position, then
continue to turn the crankshaft until a suitable
close-fitting drill can be inserted through the
hole in the cylinder block and into the
flywheel.
9Look at the distributor rotor - it should be
pointing directly at the mark you made on the
distributor body or timing cover.
10If the rotor is 180 degrees out, the No 1
piston is at TDC on the exhaust stroke.
11To get the piston to TDC on the
compression stroke, turn the crankshaft one
complete turn (360°) clockwise. The rotor
should now be pointing at the mark on the
distributor or timing cover. When the rotor is
pointing at the No 1 spark plug lead terminal
in the distributor cap and the ignition timing
marks are aligned, the No 1 piston is at TDC
on the compression stroke. Note:If it’s
impossible to align the ignition timing marks
when the rotor is pointing at the mark, the
timing belt or chain may have jumped the
teeth on the sprockets, or may have been
fitted incorrectly.
In-car engine repair procedures 2A•3
3.8 Align the notch in the pulley with the
notch on the timing plate, then check to
see if the distributor rotor is pointing to the
No 1 cylinder (if not, the camshaft is 180
degrees out - the crankshaft will have to
be rotated 360 degrees)
2A

12After the No 1 piston has been positioned
at TDC on the compression stroke, TDC for
any of the remaining pistons can be located
by turning the crankshaft and following the
firing order. Mark the remaining spark plug
lead terminal locations just like you did for the
No 1 terminal, then number the marks to
correspond with the cylinder numbers. As you
turn the crankshaft, the rotor will also turn.
When it’s pointing directly at one of the marks
on the distributor, the piston for that particular
cylinder is at TDC on the compression stroke.
4 Valve cover-
removal and refitting
1
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.
Removal
1Disconnect the battery negative cable.
2Detach the breather hose from the valve
cover.
3On M20 engines, unbolt and remove the
intake manifold support bracket and, if
applicable, the bracket for the engine sensors
or idle air stabiliser (it will probably be
necessary to disconnect the electrical
connectors from the sensors and stabiliser).
4On M30 engines, disconnect the electrical
connector for the airflow sensor. Unclip the
electrical harness, moving it out of the way.
5Where necessary on M30 engines, remove
the hoses and fittings from the intake air hose,
then loosen the clamp and separate the hose
from the throttle body. Unscrew the mounting
nuts for the air cleaner housing, and remove
the housing together with the air hose and
airflow sensor.
6Remove the valve cover retaining nuts and
washers (see illustrations). Where necessary,
disconnect the spark plug lead clip or coverfrom the stud(s), and set it aside. It will usually
not be necessary to disconnect the leads from
the spark plugs.
7Remove the valve cover and gasket.
Discard the old gasket. On the M40 engine,
also remove the camshaft cover (see
illustrations). If applicable, remove the semi-
circular rubber seal from the cut-out at the
front of the cylinder head.
Refitting
8Using a scraper, remove all traces of old
gasket material from the sealing surfaces of
the valve cover and cylinder head.
Caution: Be very careful not to
scratch or gouge the delicate
aluminium surfaces. Gasket
removal solvents are available at
motor factors, and may prove helpful.
After all gasket material has been
removed, the gasket surfaces can be
degreased by wiping them with a rag
dampened with a suitable solvent.
9If applicable, place a new semi-circular
rubber seal in the cut-out at the front of the
cylinder head, then apply RTV-type gasket
sealant to the joints between the seal and the
mating surface for the valve cover gasket.
Note:After the sealant is applied, you should
refit the valve cover and tighten the nuts within
ten minutes.
10Refit the camshaft cover (M40 engine), the
valve cover and a new gasket. Refit the
washers and nuts; tighten the nuts evenly and
securely. Don’t overtighten these nuts - theyshould be tight enough to prevent oil from
leaking past the gasket, but not so tight that
they warp the valve cover.
11The remainder of refitting is the reverse of
removal.
5 Intake manifold-
removal and refitting
2
Removal
1Allow the engine to cool completely, then
relieve the fuel pressure on fuel-injection
engines (see Chapter 4).
2Disconnect 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.
3Drain the engine coolant (see Chapter 1)
below the level of the intake manifold. If the
coolant is in good condition, it can be saved
and reused.
4On fuel injection engines, loosen the hose
clamp and disconnect the large air inlet hose
from the throttle body. It may also be
necessary to remove the entire air
cleaner/inlet hose assembly to provide
enough working room (see Chapter 4).
2A•4 In-car engine repair procedures
4.7b Removing the camshaft cover on the
M40 engine4.7a Removing the valve cover on the
M40 engine4.7c Removing the valve cover gasket on
the M40 engine
4.6b Valve cover bolt locations (arrowed)
on M20 six-cylinder engines4.6a Valve cover bolt locations (arrowed)
on M10 four-cylinder engines

6 Exhaust manifold-
removal and refitting
1
Warning: Make sure the engine is
completely cool before beginning
work on the exhaust system.
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.
1Disconnect the battery negative cable.
2On models where the air cleaner is on the
exhaust manifold side of the engine, remove
the air cleaner housing assembly and/or
airflow sensor to provide sufficient working
area (see Chapter 4, if necessary).
3Unplug the HT leads and set the spark plug
lead harness aside (see Chapter 1).
4Clearly label, then disconnect or remove, all
wires, hoses, fittings, etc. that are in the way.
Be sure to disconnect the oxygen sensor,
where fitted.
5Raise the vehicle, and support it securely
on axle stands. Working from under the
vehicle, separate the exhaust downpipe from
the manifold. Use penetrating oil on the
fasteners to ease removal (see illustrations).
6Remove the axle stands, and lower the
vehicle. Working from the ends of the
manifold toward the centre, loosen the
retaining nuts gradually until they can be
removed. Again, penetrating oil may prove
helpful.
7Pull the manifold off the head, then remove
the old gaskets (see illustrations). Note:Be
very careful not to damage the oxygen sensor,
where fitted.8Clean the gasket mating surfaces of the
head and manifold, and make sure the
threads on the exhaust manifold studs are in
good condition.
9Check for corrosion, warping, cracks, and
other damage. Repair or renew the manifold
as necessary.
10When refitting the manifold, use new
gaskets. Tighten the manifold-to-head
retaining nuts gradually, starting at the centre
and working out to the ends, to the torque
listed in this Chapter’s Specifications. Also
tighten the downpipe-to-manifold nuts.
11The remaining steps are simply a reversal
of the removal procedure.
7 Timing chain covers-
removal and refitting
5
Note 1:This procedure applies to M10 and
M30 engines.
Note 2:The upper timing chain cover can be
removed separately. If you need to remove
both the upper and lower covers, special tools
are required. Read paragraphs 8 and 9 before
beginning work.
Removal
1Disconnect 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.
2If you’re removing the lower timing chain
cover (the upper cover can be removed
separately), remove the cooling fan and fan
shroud, the radiator and the fan drivebelt
pulley (see Chapter 3).
3On the M10 engine only, remove the water
pump (see Chapter 3).
4On engines where the distributor cap is
mounted directly to the timing chain cover,
remove the cap, rotor and the black plastic
cover beneath the rotor (see Chapter 1).
5On the M30 engine fitted with the
L-Jetronic fuel system, remove the
distributor from the upper timing cover (see
Chapter 5).
6Remove the valve cover (see Section 4).
7If you’ll be removing the lower timing chain
cover on the M30 engine, remove the crankshaft
pulley from the vibration damper/hub. Hold the
pulley stationary with a socket on the centre
bolt, and remove the pulley bolts with another
socket (see illustration).
8If you’ll be removing the lower timing chain
2A•6 In-car engine repair procedures
6.7c Removing the exhaust manifold-to-
downpipe gasket (M40 engine)6.7b Removing the exhaust manifold
gasket (M40 engine)6.7a Removing the exhaust manifold
(M40 engine)
6.5b Exhaust manifold-to-downpipe flange
(M40 engine)6.5a Remove the exhaust manifold nuts
(arrowed) from the exhaust pipe (M20
engine) - soaking the nuts with penetrating
oil should make them easier to remove
Remove the windscreen
washer reservoir from the
right-hand side of the engine
compartment to give more
working room.

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

36Run the engine and check for leaks and
proper operation of all accessories, then refit
the bonnet and test drive the vehicle.
37Where necessary, have the air
conditioning system recharged and leak-
tested.
6 Engine overhaul- alternatives
The do-it-yourselfer is faced with a number
of options when performing an engine
overhaul. The decision to renew the engine
block, piston/connecting rod assemblies and
crankshaft depends on a number of factors,
with the number one consideration being the
condition of the block. Other considerations
are cost, access to machine shop facilities,
parts availability, time required to complete
the project, and the extent of prior mechanical
experience on the part of the do-it-yourselfer.
Some of the alternatives include:
Individual parts - If the inspection
procedures reveal that the engine block and
most engine components are in re-usable
condition, purchasing individual parts may be
the most economical alternative. The block,
crankshaft and piston/connecting rod
assemblies should all be inspected carefully.
Even if the block shows little wear, the
cylinder bores should be surface-honed.
Crankshaft kit- A crankshaft kit (where
available) consists of a reground crankshaft
with matched undersize new main and
connecting big-end bearings. Sometimes,
reconditioned connecting rods and new
pistons and rings are included with the kit
(such a kit is sometimes called an “engine
kit”). If the block is in good condition, but the
crankshaft journals are scored or worn, a
crankshaft kit and other individual parts may
be the most economical alternative.
Short block- A short block consists of an
engine block with a crankshaft and
piston/connecting rod assemblies already
fitted. New bearings are fitted, and all
clearances will be correct. The existing
camshaft, valve train components, cylinder
head and external parts can be bolted to the
short block with little or no machine shop
work necessary.
Full block - A “full” or “complete” block
consists of a short block plus an oil pump,
sump, cylinder head, valve cover, camshaft
and valve train components, timing sprockets
and chain (or belt) and timing cover. All
components are fitted with new bearings,
seals and gaskets used throughout. The
refitting of manifolds and external parts is all
that’s necessary.
Give careful thought to which alternative is
best for you, and discuss the situation with
local machine shops, parts dealers and
experienced rebuilders before ordering or
purchasing new parts.
7 Engine overhaul-
dismantling sequence
1It’s much easier to dismantle and work on
the engine if it’s mounted on a portable
engine stand. A stand can often be hired quite
cheaply from a tool hire shop. Before the
engine is mounted on a stand, the
flywheel/driveplate should be removed from
the engine.
2If a stand isn’t available, it’s possible to
dismantle the engine with it blocked up on the
floor. Be extra-careful not to tip or drop the
engine when working without a stand.
3If you’re going to obtain a rebuilt engine, all
the external components listed below must
come off first, to be transferred to the new
engine if applicable. This is also the case if
you’re doing a complete engine overhaul
yourself. Note:When removing the external
components from the engine, pay close
attention to details that may be helpful or
important during refitting. Note the fitted
position of gaskets, seals, spacers, pins,
brackets, washers, bolts and other small items.
Alternator and brackets
Emissions control components
Distributor, HT leads and spark plugs
Thermostat and housing cover
Water pump
Fuel injection/carburettor and fuel system
components
Intake and exhaust manifolds
Oil filter and oil pressure sending unit
Engine mounting brackets (see illustration)
Clutch and flywheel/driveplate
Engine rear plate (where applicable)
4If you’re obtaining a short block, which
consists of the engine block, crankshaft,
pistons and connecting rods all assembled,
then the cylinder head, sump and oil pump
will have to be removed as well. See Section 6
for additional information regarding the
different possibilities to be considered.
5If you’re planning a complete overhaul, the
engine must be dismantled and the internal
components removed in the following general
order:
Valve cover
Intake and exhaust manifolds
Timing belt or chain covers
Timing chain/belt
Water pump
Cylinder head
Sump
Oil pump
Piston/connecting rod assemblies
Crankshaft and main bearings
Camshaft
Rocker shafts and rocker arms (M10, M20
and M30 engines)
Cam followers and hydraulic tappets
(M40 engine)
Valve spring retainers and springs
Valves
6Before beginning the dismantling andoverhaul procedures, make sure the following
items are available. Also, refer to Section 21
for a list of tools and materials needed for
engine reassembly.
Common hand tools
Small cardboard boxes or plastic bags for
storing parts
Compartment-type metal box for storing
the hydraulic tappets (M40 engine)
Gasket scraper
Ridge reamer
Vibration damper puller
Micrometers
Telescoping gauges
Dial indicator set
Valve spring compressor
Cylinder surfacing hone
Piston ring groove cleaning tool
Electric drill motor
Tap and die set
Wire brushes
Oil gallery brushes
Cleaning solvent
8 Cylinder head- dismantling
4
1Remove the cylinder head (see Chapter 2A).
2Remove the oil supply tube from its
mounting on top of the cylinder head (see
illustrations). Note:It’s important to renew
the seals under the tube mounting bolts.
General engine overhaul procedures 2B•7
7.3 Engine left-hand mounting bracket -
M40 engine
8.2a Remove the oil tube from the top of
the cylinder head (M10 engine). Be sure to
note the location of all gaskets and
washers for reassembly
2B

the bearing - use your fingernail or the edge of
a credit card.
20Make sure the bearing faces are perfectly
clean, then apply a uniform layer of
molybdenum disulphide (“moly”) grease or
engine assembly oil to both of them. You’ll
have to push the piston into the cylinder to
expose the face of the bearing shell in the
connecting rod - be sure to slip the protective
hoses over the rod bolts first, where
applicable.
21Slide the connecting rod back into place
on the journal, and remove the protective
hoses from the rod cap bolts. Refit the rod
cap, and tighten the nuts/bolts to the
specified torque.
22Repeat the entire procedure for the
remaining pistons/connecting rods.
23The important points to remember are:
a) Keep the back sides of the bearing shells
and the insides of the connecting rods
and caps perfectly clean when
assembling them.
b) Make sure you have the correct
piston/rod assembly for each cylinder.
c) The notch or mark on the piston must
face the front of the engine.
d) Lubricate the cylinder walls with clean oil.
e) Lubricate the bearing faces when refitting
the rod caps after the oil clearance has
been checked.
24After all the piston/connecting rod
assemblies have been properly fitted, rotate
the crankshaft a number of times by hand to
check for any obvious binding.25Check the connecting rod side play (see
Section 13).
26Compare the measured side play to the
Specifications to make sure it’s correct. If it
was correct before dismantling, and the
original crankshaft and rods were refitted, it
should still be right. If new rods or a new
crankshaft were fitted, the side play may be
incorrect. If so, the rods will have to be
removed and taken to a machine shop for
attention.
27 Initial start-up and running-
in after overhaul
1
Warning:Have a fire extinguisher
handy when starting the engine
for the first time.
1Once the engine has been refitted in the
vehicle, double-check the engine oil and
coolant levels.
2With the spark plugs removed and the
ignition system disabled (see Section 3), crank
the engine until oil pressure registers on the
gauge, or until the oil pressure warning light
goes out.
3Refit the spark plugs, connect the HT leads,
and restore the ignition system functions (see
Section 3).
4Start the engine. It may take a few
moments for the fuel system to build uppressure, but the engine should start without
a great deal of effort. Note: If backfiring
occurs through the throttle body or
carburettor, check the valve timing (check that
the timing chain/belt has been correctly fitted),
the firing order (check the fitted order of the
spark plug HT leads), and the ignition timing.
5After the engine starts, it should be allowed
to warm up to normal operating temperature.
While the engine is warming up, make a
thorough check for fuel, oil and coolant leaks.
6Shut the engine off and recheck the engine
oil and coolant levels.
7Drive the vehicle to an area with minimum
traffic, accelerate at full throttle from 30 to
50 mph, then lift off the throttle completely,
and allow the vehicle to slow to 30 mph with
the throttle closed. Repeat the procedure
10 or 12 times. This will load the piston rings,
and cause them to seat properly against the
cylinder walls. Check again for oil and coolant
leaks.
8Drive the vehicle gently for the first
500 miles (no sustained high speeds) and
keep a constant check on the oil level. It is not
unusual for an engine to use oil during the
running-in period.
9At approximately 500 to 600 miles, change
the oil and filter.
10For the next few hundred miles, drive the
vehicle normally - don’t nurse it, but don’t
abuse it, either.
11After 2000 miles, change the oil and filter
again. The engine may now be considered to
be fully run-in.
2B•22 General engine overhaul procedures

3General
Coolant capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . See Chapter 1
Thermostat rating
Opening temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80°C (176°F)
Fully open at . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100°C (212°F)
Cooling fan thermo-switch - switching temperatures
Low-speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91°C (196°F)
High-speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99°C (210°F)
Torque wrench settingsNm
Mechanical cooling fan clutch-to-water pump securing
nut (left-hand thread) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Mechanical cooling fan-to-clutch bolts . . . . . . . . . . . . . . . . . . . . . . . . . 10
Water pump bolts
Small bolts (M6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Large bolts (M8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Thermostat housing bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Chapter 3
Cooling, heating and air conditioning systems
Air conditioner receiver-drier - removal and refitting . . . . . . . . . . . . 16
Air conditioning blower motor (E28/”old-shape” 5-series
models) - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Air conditioning compressor - removal and refitting . . . . . . . . . . . . . 13
Air conditioning condenser - removal and refitting . . . . . . . . . . . . . . 15
Air conditioning system - precautions and maintenance . . . . . . . . . 12
Antifreeze - general information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Coolant level check . . . . . . . . . . . . . . . . . . . . . . . . . . See Chapter 1
Coolant temperature sender unit - check and renewal . . . . . . . . . . . 8
Cooling system check . . . . . . . . . . . . . . . . . . . . . . . . See Chapter 1
Cooling system servicing (draining, flushing and refilling)See Chapter 1Engine cooling fan(s) and clutch - check, removal and refitting . . . . 5
Evaporator matrix - removal and refitting . . . . . . . . . . . . . . . . . . . . . 17
General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Heater and air conditioner control assembly - removal and refitting 10
Heater and air conditioning blower motor - removal,testing and
refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Heater matrix - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . 11
Radiator - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Thermostat - check and renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Water pump - check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Water pump - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . 7
3•1
Easy,suitable for
novice with little
experienceFairly easy,suitable
for beginner with
some experienceFairly difficult,
suitable for competent
DIY mechanic
Difficult,suitable for
experienced DIY
mechanicVery difficult,
suitable for expert
DIY or professional
Degrees of difficulty
Specifications Contents
1 General information
Engine cooling system
All vehicles covered by this manual employ
a pressurised engine cooling system, with
thermostatically-controlled coolant circulation.
An impeller-type water pump mounted on
the front of the block pumps coolant through
the engine. The coolant flows around each
cylinder, and towards the rear of the engine.
Cast-in coolant passages direct coolantaround the intake and exhaust ports, near the
spark plug areas, and in close proximity to the
exhaust valve guides.
A wax-pellet-type thermostat is located in-
line in the bottom hose on M10 engines, in a
housing near the front of the engine on M20
and M30 engines, or behind an elbow under
the timing belt upper cover (on the front of the
cylinder head) on M40 engines. During warm-
up, the closed thermostat prevents coolant
from circulating through the radiator. As the
engine nears normal operating temperature,
the thermostat opens and allows hot coolant
to travel through the radiator, where it’s
cooled before returning to the engine.The pressure in the system raises the
boiling point of the coolant, and increases the
cooling efficiency of the radiator. The cooling
system is sealed by a pressure-type cap. If
the system pressure exceeds the cap
pressure relief value, the excess pressure in
the system forces the spring-loaded valve
inside the cap off its seat, and allows the
coolant to escape through the overflow tube.
The pressure cap on four-cylinder models is
on the top of the radiator; on six-cylinder models,
it’s on top of a translucent plastic expansion
tank. The cap pressure rating is moulded into the
top of the cap. The pressure rating is either
1.0 bar (14 psi) or 1.2 bars (17 psi).

Fuel injection system - fault finding
L-Jetronic fuel injection system
Engine difficult to start, or fails to start (when cold)
Probable cause Corrective action
Cold start injector or thermotime switch faulty Test cold start injector and thermotime switch. Renew faulty components (see Section 19)
Fuel pump inoperative Check fuel pump fuse and fuel pump relay (see Sections 3 and 4)
Airflow meter flap (door) binding or stuck
in open position Inspect the airflow meter for damage (see Section 16)
Fuel pressure incorrect Test system pressure (see Section 3). Test fuel pressure regulator (Section 18)
Intake air leaks Inspect all vacuum lines, air ducts, and oil filler and dipstick seals
Fuel injectors clogged or not operating Check fuel injectors (see Section 20) and wiring harness
Coolant temperature sensor faulty or
wiring problem Test coolant temperature sensor (see Chapter 6, Section 4)
Throttle position sensor (TPS) incorrectly adjusted Check TPS adjustment (see Chapter 6, Section 4)
Incorrect ignition timing Check ignition timing (see Chapter 5). Check vacuum advance system
Dirt or other contaminants in fuel Check the fuel and drain the tank if necessary
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Engine difficult to start, or fails to start (when warm)
Probable cause Corrective action
Cold start injector leaking or operating continuously Test cold start injector and thermotime switch (see Section 19)
Fuel pressure incorrect Test fuel pump(s). Renew if necessary (see Section 3)
Insufficient residual fuel pressure Test residual fuel pressure. Renew fuel pump or fuel accumulator as necessary
(see Section 18)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks. Correct leaks as required (see Chapter 4)
Coolant temperature sensor faulty or
wiring problem Test coolant temperature sensor (see Chapter 6, Section 4)
Vapour lock (warm weather) Check fuel pressure (see Section 3)
EVAP system faulty (where applicable) Check EVAP system (see Chapter 6, Section 6)
Incorrect ignition timing Check ignition timing (see Chapter 5). Check vacuum advance system
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Idle speed control system faulty Test the idle air stabiliser valve (see Section 21)
Engine misses and hesitates under load
Probable cause Corrective action
Fuel injector clogged or faulty Test fuel injectors. Check for clogged injector lines. Renew faulty injectors (see Section 20)
Fuel pressure incorrect Test fuel system pressure (see Section 3). Test fuel pressure regulator (see Section 18)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks (see Chapter 4)
Engine maintenance Tune-up engine (see Chapter 1). Check the distributor cap, rotor, HT leads and spark
plugs, and renew any faulty components
Airflow meter flap (door) binding, or
stuck in open position Inspect the airflow meter for damage (see Section 16)
Intake air leaks Inspect all vacuum lines, air ducts and oil filler and dipstick seals
Engine has erratic idle speed
Probable cause Corrective action
Idle air stabiliser valve faulty Check the idle air stabiliser valve (see Section 21)
No power to the idle air stabiliser valve Check the idle air stabiliser relay and wiring circuit (see Chapter 12)
Vacuum advance system faulty Check vacuum advance system and electronic vacuum advance relay
Idle speed control unit faulty Have the idle speed control unit checked by a dealer
Motronic fuel injection system
Note:With this system, when faults occur, the ECU stores a fault code in its memory. These codes can only be read by a BMW dealer, as
specialised equipment is required. It may save time to have at least the initial fault diagnosis carried out by a dealer.
Lack of power
Probable cause Corrective action
Coolant temperature sensor faulty, Test coolant temperature sensor and wiring. Repair wiring or renew sensor if
or wire to sensor broken faulty (see Chapter 6)
Fuel pressure incorrect Check fuel pressure from main pump and transfer pump, as applicable (see Section 3)
Throttle plate not opening fully Check accelerator cable adjustment to make sure throttle is opening fully. Adjust cable if
necessary (see Section 9)
Fuel and exhaust systems 4•21
4

Engine difficult to start, or fails to start (when cold)
Probable cause Corrective action
Cold start injector or thermotime switch
faulty (early Motronic system only) Test cold start injector and thermotime switch. Renew faulty components (see Section 19)
Fuel pump not running Check fuel pump fuse and fuel pump relay (see Sections 2 and 3)
Airflow meter flap (door) binding, or
stuck in open position Inspect the airflow meter for damage (see Section 16)
Fuel pressure incorrect Test system pressure (see Section 3)
Intake air leaks Inspect all vacuum lines, air ducts and oil filler and dipstick seals
Fuel injectors clogged or not operating Check fuel injectors (see Section 20) and wiring harness
Coolant temperature sensor faulty or Test coolant temperature sensor (see Chapter 6, Section 4)
wiring problem
TPS (throttle position sensor) incorrectly adjusted Check TPS adjustment (see Chapter 6, Section 4)
Dirt or other contaminants in fuel Check the fuel and drain the tank if necessary
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Crankshaft position signal missing Faulty position sensor or flywheel, or reference pin missing (see Chapter 5)
Engine difficult to start, or fails to start (when warm)
Probable cause Corrective action
Cold start injector leaking or operating
continuously (early Motronic system only) Test cold start injector and thermotime switch (see Section 19)
Fuel pressure incorrect Test fuel pressure (see Section 3)
Insufficient residual fuel pressure Test fuel system hold pressure (see Section 3)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks. Correct leaks as necessary
Coolant temperature sensor faulty
or wiring problem Test coolant temperature sensor (see Chapter 6, Section 4)
Vapour lock (in warm weather) Check fuel pressure (see Section 3)
EVAP system faulty Check EVAP system (see Chapter 6, Section 6)
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Idle speed control system faulty Test the idle air stabiliser valve (see Section 21)
Oxygen sensor faulty (where applicable) Check the oxygen sensor (see Chapter 6, Section 4)
Engine misses and hesitates under load
Probable cause Corrective action
Fuel injector clogged Test fuel injectors. Check for clogged injector lines. Renew faulty injectors (see Section 20)
Fuel pressure incorrect Test fuel system pressure (see Section 3). Test fuel pressure regulator (see Section 18)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks (see Chapter 4)
Engine maintenance Tune-up engine (see Chapter 1). Check the distributor cap, rotor, HT leads and spark
plugs, and renew any faulty components
Airflow meter flap (door) binding, or Inspect the airflow meter for damage (see Section 16)
stuck in open position
Intake air leaks Inspect all vacuum lines, air ducts, and oil filler and dipstick seals
Throttle position sensor (TPS) incorrectly adjusted Check TPS adjustment (see Chapter 6)
Engine idles too fast
Probable cause Corrective action
Accelerator pedal, cable or throttle valve binding Check for worn or broken components, kinked cable, or other damage. Renew faulty
components
Air leaking past throttle valve Inspect throttle valve, and adjust or renew as required
Engine has erratic idle speed
Probable cause Corrective action
Idle air stabiliser valve faulty Check the idle air stabiliser valve (see Section 21)
No power to the idle air stabiliser valve Check the idle air stabiliser relay and wiring circuit (see Chapter 12)
Idle speed control unit faulty Have the idle speed control unit checked by a dealer
Poor fuel economy
Probable cause Corrective action
Cold start injector leaking
(early Motronic system only) Test and, if necessary, renew cold start injector (see Section 19)
Oxygen sensor faulty (where applicable) Test the oxygen sensor (see Chapter 6, Section 4))
Sticking handbrake/binding brakes Check the handbrake/braking system (see Chapter 9)
Tyre pressures low Check tyre pressures (Chapter 1)
4•22 Fuel and exhaust systems