1991 BMW 3 SERIES Cylinder head

M10, M20 and M30 engines
3Adjust all valves to their maximum clearance
by rotating the eccentric on the valve end of
the rocker arm towards the centre of the head
(see Chapter 1, if necessary).
4Before removing the thrustplate, measure
the camshaft endfloat by mounting a dial
indicator to the front end of the cylinder head,
with the probe resting on the camshaft (see
illustration). Prise the camshaft back-and-
forth in the cylinder head. The reading is the
camshaft endfloat. Compare the reading to
this Chapter’s Specifications.
5Unbolt and remove the camshaft
thrustplate. Note:There are two different
locations for the thrustplate. On M10 and M30
engines, it is attached on the front of the
cylinder head, behind the timing gear flange.
On M20 and M40 engines, the thrustplate is
located inside the head, by the rocker shafts,
at the forward end of the cylinder head.
6Remove the rear cover plate from the back
of the cylinder head (see illustration).
7Remove the retaining clips from each of the
rocker arms. Note:There is more than one
style of clip. The wire-type clips (see
illustration)are fitted one each side of the
rocker arm; the spring-steel-type goes over
the rocker arm, and clips onto either side of it.
8Before removing the rocker arm shafts,
measure the rocker arm radial clearance,
using a dial indicator, and compare your
measurement to the Specifications at thebeginning of this Chapter. Without sliding the
rocker arm along the shaft, try to rotate the
rocker arm against the shaft in each direction
(see illustration). The total movement
measured at the camshaft end of the rocker
arm is the radial clearance. If the clearance is
excessive, either the rocker arm bush, rocker
arm shaft, or both, will need to be renewed.
9Remove the rubber retaining plugs, or the
threaded plugs, at the front of the cylinder
head, as applicable. There is a plug in front of
each rocker shaft.
Caution: If your engine has
welded-in retaining plugs at the
front of the rocker shafts, take
the cylinder head to a machine
shop for plug removal, to avoid possible
damage to the cylinder head or the rocker
arm shafts.
10Rotate the camshaft until the most rocker
arms possible are loose (not compressing
their associated valve springs).
11For the remaining rocker arms that are still
compressing their valve springs, BMW
recommends using a special forked tool to
compress the rocker arms against the valve
springs (and therefore take the valve spring
tension off the camshaft lobe). If the tool is not
available, insert a standard screwdriver into the
gap above the adjuster eccentric at the valve-
end tip of each rocker arm. Using thescrewdrivers, prise the rocker arms against the
valve springs, and hold them in place as the
camshaft is removed (see the next paragraph).
At least one assistant will be necessary for this
operation, since three or four valve springs
usually need compressing. If no assistance is
available, you could try retaining the
screwdrivers that are compressing the valve
springs to the bench with lengths of sturdy wire.
Warning: Be sure the wire is
securely attached to the bench
and screwdrivers, or the
screwdrivers could fly off the cylinder
head, possibly causing injury.
12When all the rocker arms are no longer
contacting the camshaft lobes, slowly and
carefully pull the camshaft out the front of the
cylinder head. It may be necessary to rotate
the camshaft as it is removed.
Caution: Be very careful not to
scratch the camshaft bearing
journals in the cylinder head as
the camshaft is withdrawn.
13After removing the camshaft, carefully
remove the rocker arm shafts. On models
without threaded holes at the front of the
shafts, drive them out from the rear of the
cylinder head with a hammer and hardwood
dowel that is slightly smaller in diameter than
the rocker arm shaft (see illustration). For
2B•8 General engine overhaul procedures
8.13 Removing a rocker arm shaft from
the front of the cylinder head - the shaft
must be either driven out from the rear of
the head with a hardwood dowel or, on
models where the rocker shaft is threaded
at the front, pulled out from the front with
a slide-hammer-type puller
8.8 Check the rocker arm-to-shaft radial
clearance by setting up a dial indicator as
shown, and trying to rotate the rocker arm
against the shaft - DO NOT slide the rocker
arm along the shaft
8.7 Remove the retaining clips from the
rocker arms - the wire-type clip is shown
here
8.6 Remove the cover from the rear of the
cylinder head - be sure to note the
locations of any washers, gaskets and
seals while you are removing the cover8.4 To check camshaft endfloat, mount a
dial indicator so that its stem is in-line with
the camshaft and just touching the
camshaft at the front8.2b Removing the oil tube from the
camshaft bearing caps on the top of the
cylinder head (M40 engine)

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)

3When examining the bearings, remove
them from the engine block, the main bearing
caps, the connecting rods and the rod caps,
and lay them out on a clean surface in the
same general position as their location in the
engine. This will enable you to match any
bearing problems with the corresponding
crankshaft journal.
4Dirt and other foreign particles get into the
engine in a variety of ways. It may be left in
the engine during assembly, or it may pass
through filters or the crankcase ventilation
(PCV) system. It may get into the oil, and from
there into the bearings. Metal chips from
machining operations and normal engine wear
are often present. Abrasives are sometimes
left in engine components after recondi-
tioning, especially when parts are not
thoroughly cleaned using the proper cleaning
methods. Whatever the source, these foreign
objects often end up embedded in the soft
bearing material, and are easily recognised.
Large particles will not embed in the bearing,
and will score or gouge the bearing and
journal. The best prevention for this cause of
bearing failure is to clean all parts thoroughly,
and to keep everything spotlessly-clean
during engine assembly. Frequent and regular
engine oil and filter changes are also
recommended.
5Lack of lubrication (or lubrication
breakdown) has a number of interrelated
causes. Excessive heat (which thins the oil),
overloading (which squeezes the oil from the
bearing face) and oil “leakage” or “throw off”
(from excessive bearing clearances, worn oil
pump, or high engine speeds) all contribute to
lubrication breakdown. Blocked oil passages,
which usually are the result of misaligned oil
holes in a bearing shell, will also oil-starve a
bearing and destroy it. When lack of
lubrication is the cause of bearing failure, the
bearing material is wiped or extruded from the
steel backing of the bearing. Temperatures
may increase to the point where the steel
backing turns blue from overheating.
6Driving habits can have a definite effect on
bearing life. Full-throttle, low-speed operation
(labouring the engine) puts very high loads onbearings, which tends to squeeze out the oil
film. These loads cause the bearings to flex,
which produces fine cracks in the bearing
face (fatigue failure). Eventually, the bearing
material will loosen in places, and tear away
from the steel backing. Short-trip driving
leads to corrosion of bearings, because
insufficient engine heat is produced to drive
off the condensation and corrosive gases.
These products collect in the engine oil,
forming acid and sludge. As the oil is carried
to the engine bearings, the acid attacks and
corrodes the bearing material.
7Incorrect bearing refitting during engine
assembly will lead to bearing failure as well.
Tight-fitting bearings leave insufficient bearing
oil clearance, and will result in oil starvation.
Dirt or foreign particles trapped behind a
bearing shell result in high spots on the
bearing, which will lead to failure.
21 Engine overhaul-
reassembly sequence
1Before beginning engine reassembly, make
sure you have all the necessary new parts,
gaskets and seals, as well as the following
items on hand:
Common hand tools
A torque wrench
Piston ring refitting tool
Piston ring compressor
Vibration damper refitting tool
Short lengths of rubber or plastic hose to fit
over connecting rod bolts (where
applicable)
Plastigage
Feeler gauges
A fine-tooth file
New engine oil
Engine assembly oil or molybdenum
disulphide (“moly”) grease
Gasket sealant
Thread-locking compound
2In order to save time and avoid problems,
engine reassembly should be done in the
following general order:Piston rings
Crankshaft and main bearings
Piston/connecting rod assemblies
Oil pump
Sump
Cylinder head assembly
Timing belt or chain and tensioner
assemblies
Water pump
Timing belt or chain covers
Intake and exhaust manifolds
Valve cover
Engine rear plate
Flywheel/driveplate
22 Piston rings- refitting
2
1Before fitting the new piston rings, the ring
end gaps must be checked. It’s assumed that
the piston ring side clearance has been
checked and verified (see Section 18).
2Lay out the piston/connecting rod
assemblies and the new ring sets, so that the
ring sets will be matched with the same piston
and cylinder during the end gap measurement
and engine assembly.
3Insert the top ring into the first cylinder, and
square it up with the cylinder walls by pushing
it in with the top of the piston (see illustration).
The ring should be near the bottom of the
cylinder, at the lower limit of ring travel.
4To measure the end gap, slip feeler gauges
between the ends of the ring until a gauge equal
to the gap width is found(see illustration). The
feeler gauge should slide between the ring ends
with a slight amount of drag. Compare the
measurement to this Chapter’s Specifications.
If the gap is larger or smaller than specified,
double-check to make sure you have the
correct rings before proceeding.
5If the gap is too small, it must be enlarged,
or the ring ends may come in contact with
each other during engine operation, which
can cause serious damage to the engine. The
end gap can be increased by filing the ring
ends very carefully with a fine file. Mount the
2B•18 General engine overhaul procedures
22.5 If the end gap is too small, clamp a
file in a vice, and file the ring ends (from
the outside in only) to enlarge the gap
slightly22.4 With the ring square in the cylinder,
measure the end gap with a feeler gauge22.3 When checking piston ring end gap,
the ring must be square in the cylinder
bore (this is done by pushing the ring down
with the top of a piston as shown)

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).