light BMW 3 SERIES 1987 E30 Owner's Guide

7Wipe the oil out of the cylinder, and repeat
the procedure for the remaining cylinders.
8After the honing job is complete, chamfer
the top edges of the cylinder bores with a
small file, so the rings won’t catch when the
pistons are refitted. Be very careful not to nick
the cylinder walls with the end of the file.
9The entire engine block must be washed
again very thoroughly with warm, soapy
water, to remove all traces of the abrasive grit
produced during the honing operation. Note:
The bores can be considered clean when a
lint-free white cloth - dampened with clean
engine oil - used to wipe them out doesn’t
pick up any more honing residue, which will
show up as grey areas on the cloth.Be sure to
run a brush through all oil holes and galleries,
and flush them with running water.
10After rinsing, dry the block, and apply a
coat of light rust-preventive oil to all machined
surfaces. Wrap the block in a plastic bag to
keep it clean, and set it aside until
reassembly.
18 Pistons/connecting rods-
inspection
3
1Before the inspection process can be
carried out, the piston/connecting rod
assemblies must be cleaned and the original
piston rings removed from the pistons.Note:
Always use new piston rings when the engine
is reassembled.
2Using a piston ring refitting tool, carefully
remove the rings from the pistons. Be careful
not to nick or gouge the pistons in the
process (see illustration).
3Scrape all traces of carbon from the top of
the piston. A hand-held wire brush or a piece
of fine emery cloth can be used once the
majority of the deposits have been scraped
away. Do not, under any circumstances, use a
wire brush mounted in a drill motor to remove
deposits from the pistons. The piston material
is soft, and may be damaged by the wire
brush.
4Use a piston ring groove cleaning tool to
remove carbon deposits from the ring
grooves. Be very careful to remove only thecarbon deposits - don’t remove any metal,
and do not nick or scratch the sides of the
ring grooves (see illustration).
5Once the deposits have been removed,
clean the piston/rod assemblies with solvent,
and dry them with compressed air (if
available). Make sure the oil return holes in the
back sides of the ring grooves are clear.
6If the pistons and cylinder walls aren’t
damaged or worn excessively, and if the
engine block is not rebored, new pistons
won’t be necessary. Normal piston wear
appears as even vertical wear on the piston
thrust surfaces (90° to the gudgeon pin bore),
and slight looseness of the top ring in its
groove. New piston rings, however, should
always be used when an engine is rebuilt.
7Carefully inspect each piston for cracks
around the skirt, at the pin bosses, and at the
ring lands.
8Look for scoring and scuffing on the thrust
faces of the skirt, holes in the piston crown,
and burned areas at the edge of the crown. If
the skirt is scored or scuffed, the engine may
have been suffering from overheating and/or
abnormal combustion, which caused
excessively high operating temperatures. The
cooling and lubrication systems should be
checked thoroughly. A hole in the piston crown
is an indication that abnormal combustion (pre-
ignition) was occurring. Burned areas at the
edge of the piston crown are usually evidence
of spark knock (detonation). If any of the aboveproblems exist, the causes must be corrected,
or the damage will occur again. The causes
may include intake air leaks, incorrect fuel/air
mixture, or incorrect ignition timing. On later
vehicles with high levels of exhaust emission
control, including catalytic converters, the
problem may be with the EGR (exhaust gas
recirculation) system, where applicable.
9Corrosion of the piston, in the form of small
pits, indicates that coolant is leaking into the
combustion chamber and/or the crankcase.
Again, the cause must be corrected or the
problem may persist in the rebuilt engine.
10Measure the piston ring side clearance by
laying a new piston ring in each ring groove
and slipping a feeler gauge in beside it(see
illustration). Check the clearance at three or
four locations around each groove. Be sure to
use the correct ring for each groove - they are
different. If the side clearance is greater than
the figure listed in this Chapter’s Specifi-
cations, new pistons will have to be used.
11Check the piston-to-bore clearance by
measuring the bore (see Section 16) and the
piston diameter. Make sure the pistons and
bores are correctly matched. Measure the
piston across the skirt, at 90° to, and in line
with, the gudgeon pin (see illustration). (Any
difference between these two measurements
indicates that the piston is no longer perfectly
round.) Subtract the piston diameter from the
bore diameter to obtain the clearance. If it’s
greater than specified, the block will have to
be rebored, and new pistons and rings fitted.
2B•16 General engine overhaul procedures
18.11 Measure the piston diameter at a
90-degree angle to the gudgeon pin, at the
same height as the gudgeon pin
18.10 Check the ring side clearance with a
feeler gauge at several points around the
groove18.4 The piston ring grooves can be
cleaned with a special tool, as shown
here18.2 Removing the compression rings with
a ring expander - note the mark (arrowed)
facing up
If a groove cleaning tool isn’t available,
a piece broken off the old ring will do
the job, but protect your hands - piston
rings can be sharp

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)

file in a vice equipped with soft jaws, slip the
ring over the file, with the ends contacting the
file face, and slowly move the ring to remove
material from the ends. When performing this
operation, file only from the outside in(see
illustration).
6Excess end gap isn’t critical unless it’s
greater than 1.0 mm. Again, double-check to
make sure you have the correct rings for your
engine.
7Repeat the procedure for each ring that will
be fitted in the first cylinder and for each ring
in the remaining cylinders. Remember to keep
rings, pistons and cylinders matched up.
8Once the ring end gaps have been
checked/corrected, the rings can be fitted on
the pistons.
9The oil control ring (lowest one on the
piston) is usually fitted first. It’s normally
composed of three separate components.
Slip the spacer/expander into the groove(see
illustration). If an anti-rotation tang is used,
make sure it’s inserted into the drilled hole in
the ring groove. Next, refit the lower side rail.
Don’t use a piston ring refitting tool on the oil
ring side rails, as they may be damaged.
Instead, place one end of the side rail into the
groove between the spacer/expander and the
ring land, hold it firmly in place, and slide a
finger around the piston while pushing the rail
into the groove(see illustration). Next, refit
the upper side rail in the same manner.
10After the three oil ring components have
been fitted, check to make sure that both the
upper and lower side rails can be turned
smoothly in the ring groove.
11The middle ring is fitted next. It’s usually
stamped with a mark which must face up,
towards the top of the piston. Note:Always
follow the instructions printed on the ring
package or box - different manufacturers may
require different approaches. Do not mix up
the top and middle rings, as they have
different cross-sections.
12Make sure the identification mark is facing
the top of the piston, then slip the ring into the
middle groove on the piston (see illus-
tration 18.2). Don’t expand the ring any more
than necessary to slide it over the piston. Use
a proper ring-fitting tool if available; with care,
old feeler gauges can be used to prevent the
rings dropping into empty grooves.13Refit the top ring in the same manner.
Make sure the mark is facing upwards. Be
careful not to confuse the top and middle
rings.
14Repeat the procedure for the remaining
pistons and rings.
23 Intermediate shaft- refitting
5
1Clean the intermediate shaft bearing
surfaces and the pressed-in bearing sleeves
in the cylinder block.
2Lubricate the shaft, and slide it into the
block.
3Refit the two bolts that hold the retaining
plate to the block.
4The remainder of the parts are fitted in the
reverse order of removal.
24 Crankshaft- refitting and
main bearing oil clearance
check
4
1Crankshaft refitting is the first major step in
engine reassembly. It’s assumed at this point
that the engine block and crankshaft have
been cleaned, inspected, and repaired or
reconditioned.
2Position the block upside-down.
3Remove the main bearing cap bolts, and liftout the caps. Lay them out in the proper order
to ensure correct refitting.
4If they’re still in place, remove the original
bearing shells from the block and the main
bearing caps. Wipe the bearing surfaces of
the block and caps with a clean, lint-free
cloth. They must be kept spotlessly-clean.
Main bearing oil clearance
check
5Clean the back sides of the new main
bearing shells, and lay one in each main
bearing saddle in the block. If one of the
bearing shells from each set has a large
groove in it, make sure the grooved shell is
fitted in the block. Lay the other bearing from
each set in the corresponding main bearing
cap. Make sure the tab on the bearing shell
fits into the recess in the block or cap.
Caution: The oil holes in the
block must line up with the oil
holes in the bearing shell. Do not
hammer the bearing into place,
and don’t nick or gouge the bearing faces.
No lubrication should be used at this time.
6The flanged thrust bearing must be fitted in
the No 3 bearing cap and saddle in the M10
engine, in the No 6 bearing cap and saddle in
the M20 engine (see illustration), in the No 4
bearing cap and saddle in the M30 engine,
and in the No 4 bearing saddle only in the
M40 engine.
7Clean the faces of the bearings in the block
and the crankshaft main bearing journals with
a clean, lint-free cloth.
8Check or clean the oil holes in the
crankshaft, as any dirt here can go only one
way - straight through the new bearings.
9Once you’re certain the crankshaft is clean,
carefully lay it in position in the main bearings.
10Before the crankshaft can be permanently
fitted, the main bearing oil clearance must be
checked.
11Cut several pieces of the appropriate-size
Plastigage (they must be slightly shorter than
the width of the main bearings), and place one
piece on each crankshaft main bearing
journal, parallel with the crankshaft centreline
(see illustration).
12Clean the faces of the bearings in the
caps, and refit the caps in their respective
General engine overhaul procedures 2B•19
22.9b DO NOT use a piston ring refitting
tool when refitting the oil ring side rails22.9a Refitting the spacer/expander in the
oil control ring groove
24.11 Lay the Plastigage strips on the
main bearing journals, parallel to the
crankshaft centreline24.6 Refitting a thrust main bearing (note
the flanges) in the engine block bearing
saddle
2B

positions (don’t mix them up) with the arrows
pointing towards the front of the engine. Don’t
disturb the Plastigage.
13Starting with the centre main bearing and
working out toward the ends, progressively
tighten the main bearing cap bolts to the
torque listed in this Chapter’s Specifications.
On M10, M20 and M30 engines, tighten the
bolts in three stages. On the M40 engine,
tighten all the bolts initially to the Stage 1
torque, then angle-tighten them by the angle
given in the Specifications. Carry out the
angle-tightening on each bolt in one
controlled movement. Don’t rotate the
crankshaft at any time during the tightening
operation.
14Remove the bolts and carefully lift off the
main bearing caps. Keep them in order. Don’t
disturb the Plastigage or rotate the
crankshaft. If any of the main bearing caps are
difficult to remove, tap them gently from side-
to-side with a soft-face hammer to loosen
them.
15Compare the width of the crushed
Plastigage on each journal to the scale printed
on the Plastigage envelope to obtain the main
bearing oil clearance (see illustration). Check
the Specifications to make sure it’s correct.
16If the clearance is not as specified, thebearing shells may be the wrong size (which
means different ones will be required). Before
deciding that different shells are needed,
make sure that no dirt or oil was between the
bearing shells and the caps or block when the
clearance was measured. If the Plastigage
was wider at one end than the other, the
journal may be tapered (see Section 19).
17Carefully scrape all traces of the
Plastigage material off the main bearing
journals and/or the bearing faces. Use your
fingernail or the edge of a credit card - don’t
nick or scratch the bearing faces.
Final crankshaft refitting
18Carefully lift the crankshaft out of the
engine.
19Clean the bearing faces in the block, then
apply a thin, uniform layer of molybdenum
disulphide (“moly”) grease or engine oil to
each of the bearing surfaces. Be sure to coat
the thrust faces as well as the journal face of
the thrust bearing.
20Make sure the crankshaft journals are
clean, then lay the crankshaft back in place in
the block.
21Clean the faces of the bearings in the
caps, then apply engine oil to them.
22Refit the caps in their respective
positions, with the arrows pointing towards
the front of the engine.
23Refit the bolts finger-tight.
24Lightly tap the ends of the crankshaft
forward and backward with a lead or brass
hammer, to line up the main bearing and
crankshaft thrust surfaces.
25Tighten the bearing cap bolts to the
specified torque, working from the centre
outwards. On M10, M20 and M30 engines,
tighten the bolts in three stages to the final
torque, leaving out the thrust bearing cap
bolts at this stage. On M40 engines, tighten all
of the bolts in the two stages given in the
Specifications.
26On M10, M20 and M30 engines, tighten
the thrust bearing cap bolts to the torque
listed in this Chapter’s Specifications.
27On manual transmission models, fit a new
pilot bearing in the end of the crankshaft (see
Chapter 8).28Rotate the crankshaft a number of times
by hand to check for any obvious binding.
29The final step is to check the crankshaft
endfloat with a feeler gauge or a dial indicator
as described in Section 13. The endfloat
should be correct, providing the crankshaft
thrust faces aren’t worn or damaged, and new
bearings have been fitted.
30Fit the new seal, then bolt the housing to
the block (see Section 25).
25 Crankshaft rear oil seal-
refitting
3
1The crankshaft must be fitted first, and the
main bearing caps bolted in place. The new
seal should then be fitted in the retainer, and
the retainer bolted to the block.
2Before refitting the crankshaft, check the
seal contact surface very carefully for
scratches and nicks that could damage the
new seal lip and cause oil leaks. If the
crankshaft is damaged, the only alternative is
a new or different crankshaft, unless a
machine shop can suggest a means of repair.
3The old seal can be removed from the
housing with a hammer and punch by driving
it out from the back side (see illustration). Be
sure to note how far it’s recessed into the
housing bore before removing it; the new seal
will have to be recessed an equal amount. Be
very careful not to scratch or otherwise
damage the bore in the housing, or oil leaks
could develop.
4Make sure the retainer is clean, then apply
a thin coat of engine oil to the outer edge of
the new seal. The seal must be pressed
squarely into the housing bore, so hammering
it into place is not recommended. At the very
least, use a block of wood as shown, or a
section of large-diameter pipe (see
illustration). If you don’t have access to a
press, sandwich the housing and seal
between two smooth pieces of wood, and
press the seal into place with the jaws of a
large vice. The pieces of wood must be thick
enough to distribute the force evenly around
the entire circumference of the seal. Work
2B•20 General engine overhaul procedures
25.5 Lubricate the lip of the seal, and bolt
the retainer to the rear of the engine block25.4 Drive the new seal into the retainer
with a wooden block or a section of pipe, if
you have one large enough - make sure
the seal enters the retainer bore squarely25.3 After removing the retainer from the
block, support it on two wooden blocks,
and drive out the old seal with a punch and
hammer
24.15 Compare the width of the crushed
Plastigage to the scale on the envelope to
determine the main bearing oil clearance
(always take the measurement at the
widest point of the Plastigage); be sure to
use the correct scale - standard and
metric ones are included

slowly, and make sure the seal enters the bore
squarely.
5The seal lips must be lubricated with multi-
purpose grease or clean engine oil before the
seal/retainer is slipped over the crankshaft
and bolted to the block (see illustration). Use
a new gasket - no sealant is required - and
make sure the dowel pins are in place before
refitting the retainer.
6Tighten the retainer nuts/screws a little at a
time until they’re all snug, then tighten them to
the torque listed in the Specifications in
Chapter 2A.
26 Pistons/connecting rods-
refitting and big-end bearing
oil clearance check
4
1Before refitting the piston/connecting rod
assemblies, the cylinder walls must be
perfectly clean, the top edge of each cylinder
must be chamfered, and the crankshaft must
be in place.
2Remove the cap from the end of No 1
connecting rod (refer to the marks made
during removal). Remove the original bearing
shells, and wipe the bearing surfaces of the
connecting rod and cap with a clean, lint-free
cloth. They must be kept spotlessly-clean.
Connecting rod big-end bearing
oil clearance check
3Clean the back side of the new upper
bearing shell, then lay it in place in the
connecting rod. Make sure the tab on the
bearing fits into the recess in the rod. Don’t
hammer the bearing shell into place, and be
very careful not to nick or gouge the bearing
face. Don’t lubricate the bearing at this time.
4Clean the back side of the other bearing
shell, and refit it in the rod cap. Again, make
sure the tab on the bearing fits into the recess
in the cap, and don’t apply any lubricant. It’s
critically important that the mating surfaces of
the bearing and connecting rod are perfectlyclean and oil-free when they’re assembled for
this check.
5Position the piston ring gaps so they’re
staggered 120° from each other.
6Where applicable, slip a section of plastic
or rubber hose over each connecting rod cap
bolt.
7Lubricate the piston and rings with clean
engine oil, and attach a piston ring
compressor to the piston. Leave the skirt
protruding about 6 or 7 mm to guide the
piston into the cylinder. The rings must be
compressed until they’re flush with the piston.
8Rotate the crankshaft until the No 1
connecting rod journal is at BDC (bottom
dead centre). Apply a coat of engine oil to the
cylinder walls.
9With the mark or notch on top of the piston
facing the front of the engine, gently insert the
piston/connecting rod assembly into the No 1
cylinder bore, and rest the bottom edge of the
ring compressor on the engine block.
10Tap the top edge of the ring compressor
to make sure it’s contacting the block around
its entire circumference.
11Gently tap on the top of the piston with
the end of a wooden hammer handle (see
illustration)while guiding the end of the
connecting rod into place on the crankshaft
journal. Work slowly, and if any resistance is
felt as the piston enters the cylinder, stop
immediately. Find out what’s catching, and fix
it before proceeding. Do not, for any reason,
force the piston into the cylinder - you might
break a ring and/or the piston.
12Once the piston/connecting rod assembly
is fitted, the connecting rod big-end bearing
oil clearance must be checked before the rod
cap is permanently bolted in place.13Cut a piece of the appropriate-size
Plastigage slightly shorter than the width of
the connecting rod big-end bearing,
and lay it in place on the No 1 connecting rod
journal, parallel with the crankshaft centre-
line.
14Clean the connecting rod cap bearing
face, remove the protective hoses from the
connecting rod bolts, and refit the rod cap.
Make sure the mating mark on the cap is on
the same side as the mark on the connecting
rod.
15Refit the nuts/bolts, and tighten them to
the torque listed in this Chapter’s Specifica-
tions. On M10 and M30 engines, work up to
the final torque in three stages. Note:Use a
thin-wall socket, to avoid erroneous torque
readings that can result if the socket is
wedged between the rod cap and nut. If the
socket tends to wedge itself between the nut
and the cap, lift up on it slightly until it no
longer contacts the cap. Do not rotate the
crankshaft at any time during this operation.
16Undo the nuts and remove the rod cap,
being very careful not to disturb the
Plastigage.
17Compare the width of the crushed
Plastigage to the scale printed on the
Plastigage envelope to obtain the oil
clearance (see illustration). Compare it to the
Specifications to make sure the clearance is
correct.
18If the clearance is not as specified, the
bearing shells may be the wrong size (which
means different ones will be required). Before
deciding that different shells are needed,
make sure that no dirt or oil was between the
bearing shells and the connecting rod or cap
when the clearance was measured. Also,
recheck the journal diameter. If the Plastigage
was wider at one end than the other, the
journal may be tapered (see Section 19).
Final connecting rod refitting
19Carefully scrape all traces of the
Plastigage material off the rod journal and/or
bearing face. Be very careful not to scratch
General engine overhaul procedures 2B•21
26.17 Measuring the width of the crushed Plastigage to
determine the big-end bearing oil clearance (be sure to use the
correct scale - standard and metric ones are included)26.11 Drive the piston gently into the cylinder bore with the end of
a wooden or plastic hammer handle
2B
The piston rings may try to
pop out of the ring
compressor just before
entering the cylinder bore, so
keep some downward pressure on the
ring compressor

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

Warning: Do not remove the
pressure cap from the radiator or
expansion tank until the engine
has cooled completely and
there’s no pressure remaining in the
cooling system. Removing the cap from a
hot engine risks personal injury by
scalding.
Heating system
The heating system consists of a blower fan
and heater matrix located in the heater box,
with hoses connecting the heater matrix to the
engine cooling system, and the heater/air
conditioning control head on the dashboard.
Hot engine coolant is circulated through the
heater matrix passages all the time the engine
is running. Switching the heater on opens a
flap door to direct air through the heater
matrix, and the warmed air enters the
passenger compartment. A fan switch on the
control head activates the blower motor,
which forces more air through the heater
matrix, giving additional heater output for
demisting, etc.
Air conditioning system
The air conditioning system consists of a
condenser mounted in front of the radiator, an
evaporator mounted adjacent to the heater
matrix, a compressor mounted on the engine,
a filter-drier (receiver-drier) which contains a
high-pressure relief valve, and the plumbing
connecting all of the above components.
A blower fan forces the warmer air of the
passenger compartment through the
evaporator matrix (a radiator-in-reverse),
transferring the heat from the air to the
refrigerant. The liquid refrigerant boils off into
low-pressure vapour, taking the heat with it
when it leaves the evaporator.
Note: Refer to the precautions at the start
of Section 12 concerning the potential
dangers associated with the air conditioning
system.
2 Antifreeze-
general information
Warning: Do not allow antifreeze
to come in contact with your skin
or painted surfaces of the
vehicle. Rinse off spills
immediately with plenty of water. If
consumed, antifreeze can be fatal;
children and pets are attracted by its
sweet taste, so wipe up garage floor and
drip pan coolant spills immediately. Keep
antifreeze containers covered, and repair
leaks in your cooling system as soon as
they are noticed.
The cooling system should be filled with a
60/40% water/ethylene-glycol-based anti-
freeze solution, which will prevent freezing
down to approximately -27°C (-17°F). The
antifreeze also raises the boiling point of thecoolant, and (if of good quality) provides
protection against corrosion.
The cooling system should be drained,
flushed and refilled at the specified intervals
(see Chapter 1). Old or contaminated
antifreeze solutions are likely to cause
damage, and encourage the formation of rust
and scale in the system. Use distilled water
with the antifreeze, if available, or clean
rainwater. Tap water will do, but not if the
water in your area is at all “hard”.
Before adding antifreeze, check all hose
connections, because antifreeze tends to
search out and leak through very minute
openings. Engines don’t normally consume
coolant, so if the level goes down, find the
cause and correct it.
The antifreeze mixture should be
maintained at its correct proportions; adding
too much antifreeze reduces the efficiency of
the cooling system. If necessary, consult the
mixture ratio chart on the antifreeze container
before adding coolant. Hydrometers are
available at most car accessory shops to test
the coolant. Use antifreeze which meets the
vehicle manufacturer’s specifications.
3 Thermostat-
check and renewal
1
Warning: Do not remove the
radiator cap, drain the coolant, or
renew the thermostat until the
engine has cooled completely.
Check
1Before assuming the thermostat is to blame
for a cooling system problem, check the
coolant level, drivebelt tension (see Chapter 1)
and temperature gauge (or warning light)
operation.
2If the engine seems to be taking a long time
to warm up (based on heater output or
temperature gauge operation), the thermostat
is probably stuck open. Renew the
thermostat.
3If the engine runs hot, use your hand to
check the temperature of the upper radiator
hose. If the hose isn’t hot, but the engine is,
the thermostat is probably stuck closed,preventing the coolant inside the engine from
circulating to the radiator. Renew the
thermostat.
Caution: Don’t drive the vehicle
without a thermostat. The engine
will be very slow to warm-up in
cold conditions, resulting in poor
fuel economy and driveability. A new
thermostat is normally an inexpensive
component anyway.
4If the upper radiator hose is hot, it means
that the coolant is flowing and the thermostat
is at least partly open. Consult the “Fault
finding” Section at the rear of this manual for
cooling system diagnosis.
Renewal
All models
5Disconnect the negative cable from the
battery.
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.
6Drain the cooling system (see Chapter 1). If
the coolant is relatively new or in good
condition, save it and re-use it.
M10 engines
7The thermostat is located in the bottom
hose. First remove the cooling fan.
8Note the fitted position of the thermostat,
then unscrew the hose clamps and withdraw
the thermostat from the hose connections
(see illustration).
9Refit the thermostat-to-hose connections,
and tighten the hose clamps.
10Refit the cooling fan.
M20 and M30 engines
11Loosen the hose clamp (see illustration),
then detach the hose(s) from the thermostat
cover.
3•2 Cooling, heating and air conditioning systems
3.11 On M20 and M30 engine models,
loosen the hose clamp (A) and disconnect
the hose from the thermostat housing
cover - note that the coolant temperature
sender unit (barely visible behind the fuel
pressure regulator) is located at the top of
the thermostat housing (B)
3.8 On the M10 (four-cylinder) engine, the
thermostat (arrowed) is connected in-line
in the radiator hose

disconnect the fluid cooler lines from the
radiator. Use a drip tray to catch spilled fluid.
Plug the fluid cooler lines and fittings.
7Disconnect the coolant sensors located on
the radiator (see illustration). The thermo-
statically-controlled switches for high- and
low-speed operation of the auxiliary fan are
located in the radiator tanks, in various
locations depending on engine and model.
8Remove the radiator mounting bolt(s). The
mountings are either on the top or sides of the
radiator (see illustration).
9Carefully lift out the radiator from the
bottom mountings, taking care not to damage
the cooling fins. Don’t spill coolant on the
vehicle, or scratch the paint.
10With the radiator removed, it can be
inspected for leaks and damage. If it needs
repair, have a specialist perform the work, as
special techniques are required.
11Flies and dirt can be removed from the
radiator with compressed air and a soft brush.
Don’t bend the cooling fins as this is done.
12Check the radiator mountings for
deterioration, and renew if necessary (see
illustration).
Refitting
13Refitting is the reverse of the removal
procedure.
14After refitting, fill the cooling system with
the proper mixture of antifreeze and water.
Refer to Chapter 1 if necessary.15Start the engine and check for leaks.
Allow the engine to reach normal operating
temperature, indicated by the upper radiator
hose becoming hot. Recheck the coolant
level, and add more if required.
16If you’re working on an automatic
transmission model, check and add
transmission fluid as needed.
5 Engine cooling fan(s) and
clutch- check, removal and
refitting
1
Warning: To avoid possible injury
or damage, DO NOT operate the
engine with a damaged fan. Do
not attempt to repair fan blades -
fit a new fan. Also, the electric auxiliary fan
in front of the radiator or air conditioning
condenser can come on without the
engine running or ignition being on. It is
controlled by the coolant temperature of
the thermo-switches located in the
radiator.
Check
Electric auxiliary fan
Note: This fan on most models is controlled
by two thermo-switches placed in the radiator:
one for low-speed/low-temperature operation,
and one for high-speed/high-temperature
operation. Each switch comes on at a different
coolant temperature (refer to the Specifica-
tions at the beginning of this Chapter).
1The thermostatically-controlled switches for
high- and low-speed operation of the auxiliary
fan are fitted in various locations in the
radiator (see illustration 4.7), depending on
engine or model. Two single switches, or one
dual switch, may be fitted.
2Insert a small screwdriver into the
connector to lift the lock tab, and unplug the
fan wire harness.
3To test the fan motor, unplug the electrical
connector at the motor, and use jumper wires
to connect the fan directly to the battery. If the
fan doesn’t work when connected directly to
the battery, the motor is proved faulty, and
must be renewed. If the fan works, there’s agood chance the switch is malfunctioning. To
more accurately diagnose the problem, follow
the steps that apply to your model. Note: Spin
the auxiliary fan motor by hand, to check that
the motor or fan isn’t binding. Make sure,
however, that the engine is sufficiently cool
that there is no danger of the fan cutting-in on
its own when this is done.
4To test the low-speed and high-speed
circuits, disconnect the electrical connector
from one of the fan switches, and bridge the
terminals of the switch’s electrical connector
with a short piece of wire. The fan should run
at low or high speed, depending on which
switch has been disconnected. On some
models the ignition must be on before the fan
will run.
5Repeat the test at the other switch so that
both high and low speeds are tested.
6If the low-speed and high-speed circuits
are OK, but there has been a problem with the
fan not operating correctly in service, renew
the switch (or switches). To remove a switch,
drain the coolant below the level of the switch
(see Chapter 1), then unscrew the switch and
screw in the new one. Refill the system with
coolant.
7If the switches are satisfactory, but the
motor still does not operate, the problem lies
in the fuse, the relay, the wiring which
connects the components (or the fan motor
itself). Carefully check the fuse, relay, all
wiring and connections. See Chapter 12 for
more information on how to carry out these
checks.
Mechanical fan with viscous clutch
8Disconnect the battery negative cable, and
rock the fan back and forth by hand to check
for excessive bearing play.
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.
9With the engine cold, turn the fan blades by
hand. The fan should turn with slight
resistance.
10Visually inspect for substantial fluid
leakage from the fan clutch assembly. If
problems are noted, renew the fan clutch
assembly.
11With the engine completely warmed up,
turn off the ignition switch and disconnect the
battery negative cable. Turn the fan by hand.
Heavier resistance should be evident. If the
fan turns easily, a new fan clutch may be
needed.
Removal and refitting
Electric auxiliary fan
12Disconnect the battery negative cable.
13To remove the auxiliary fan follow the
procedure that applies to your vehicle.
3•4 Cooling, heating and air conditioning systems
4.12 When the radiator is out, the radiator
mountings can be inspected - check for
signs of deterioration, and renew them, if
needed
4.8 The radiator is bolted to the front
panel at either the sides or the top of the
radiator4.7 Sensors that control the high- and
low-speed operation of the auxiliary
cooling fan are located in various places in
the radiator tanks

3-Series models
14Remove the radiator grille assembly (see
Chapter 11).
15Unbolt and remove the fan bracket and
shroud assembly from the radiator (see
Section 5).
16Remove the radiator (see Section 4).
17Unbolt the air conditioning condenser
mounting bolts, where applicable. Do not
remove the condenser or disconnect any
refrigerant lines from the condenser.
18Carefully pull the condenser back towards
the engine, slightly, to gain access to lift the
auxiliary fan.
19Disconnect the fan motor electrical
connection and remove the auxiliary fan.
20Refitting is the reverse of removal.
5-Series models
21Remove the screws and trim panel in front
of the radiator.
22Unbolt the fan assembly from the
condenser mounting points.
23Disconnect the fan electrical connector.
24Remove the fan and housing from the car,
being careful not to damage the air
conditioning condenser (when applicable)
while removing the fan.
25Refitting is the reverse of removal.
Mechanical fan with viscous clutch
26Disconnect the battery negative cable.
Remove the fan shroud mounting screws or
plastic fasteners, and detach the shroud (see
Section 4).
27 Use a 32 mm open-ended spanner to
remove the fan/clutch assembly. Place the
spanner on the large nut ahead of the pulley
(see illustrations), and tap the end of the
spanner to loosen the nut.
Caution: The nut has left-handed
threads, so it loosens by being
turned clockwise, as viewed from
the front of the vehicle.
28Lift the fan/clutch assembly (and shroud,
if necessary) out of the engine compartment.
29If necessary, remove the four bolts
attaching the pulley to the water pump hub.
The pulley can then be removed after
removing the drivebelt(s) (see illustration).30Carefully inspect the fan blades for
damage and defects. Renew it if necessary.
31At this point, the fan may be unbolted
from the clutch, if necessary. If the fan clutch
is stored, position it with the radiator side
facing down.
32Refitting is the reverse of removal.
6 Water pump- check
1
1A failure in the water pump can cause
serious engine damage due to overheating.
2There are two ways to check the operation
of the water pump while it’s fitted on the
engine. If either of the following checks
suggest that the pump is defective, a new one
should be fitted.
3Water pumps are equipped with “weep” or
“vent” holes. If a failure occurs in the pump
seal, coolant will leak from the hole. In most
cases, you’ll need a torch to find the hole on
the water pump from underneath to check for
leaks.
4If the water pump shaft bearings fail, there
may be a howling sound at the front of the
engine while it’s running. Shaft wear can be
felt if the water pump pulley is rocked up and
down (with the drivebelt removed). Don’t
mistake drivebelt slippage, which causes a
squealing sound, for water pump bearing
failure. Alternator bearing failure can also
cause a howling sound, but after removing the
drivebelt(s) it should be easy enough to tell
which component is responsible.
7 Water pump-
removal and refitting
2
Warning: Wait until the engine is
completely cool before beginning
this procedure.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.
2Drain the cooling system (see Chapter 1). If
the coolant is relatively new, or in good
condition, save it and re-use it.
3Remove the cooling fan shroud (see
Section 5).
4Remove the drivebelts (see Chapter 1).
5Where applicable, loosen the clamps and
detach the hoses from the water pump. If
they’re stuck, grasp each hose near the end
with a pair of water pump pliers and gently
twist it to break the seal, then pull it off. If the
hoses are deteriorated, cut them off and refit
new ones.
6Remove the fan and clutch assembly and
the pulley at the end of the water pump shaft
(see Section 5).
7To remove the water pump, follow the
specific steps that apply to your engine.
M10 engine
8Unscrew the mounting bolts and remove
the water pump (see illustration).
Cooling, heating and air conditioning systems 3•5
5.29 Removing the water pump pulley
(M40 engine)5.27b . . . to loosen the nut, place a 32 mm
open-ended spanner on the nut, and
sharply strike the spanner (A) with a metal
drift (B) and hammer; this will loosen the
nut and allow it to be turned easily so the
fan can be removed5.27a The cooling fan on the water pump
is attached to the shaft by a left-hand-
threaded nut located directly behind the
fan . . .
7.8 On M10 engines, there are seven bolts
(locations arrowed) that hold the water
pump to the block
3

12Disconnect the cables from the clips
securing them to the lever assembly, marking
them for accurate refitting.
13Disconnect the electrical connection from
the control assembly.
14Remove the screws attaching the bezel to
the control assembly, and remove the control
assembly.
Refitting
15Refitting is the reverse of the removal
procedure.
11 Heater matrix-
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.
1Disconnect the battery negative cable.
2Drain the cooling system (see Chapter 1).
3Remove the centre console (see Chap-
ter 11). Spread an old blanket over the front
carpeting; this will prevent stains if any
residual coolant spills.
Removal
3-Series models
4Remove the left-hand side heater ducting,
and set it aside.
5Remove the heater valve clamp.
6Remove the screws and detach the flange
where the two coolant lines enter the heater
matrix case. Be careful; some coolant may
spill.
7Remove the two screws holding the heater
matrix case to the heater main assembly.
8Slide the heater matrix out of the mounting.
Be careful not to spill any of the remaining
coolant in the heater matrix when removing it.
5-Series models
9Disconnect the temperature sensor
electrical connectors.
10Disconnect the straps holding the wiring
to the case, and set the wiring out of the way.
11Unfasten the cover fasteners.
12Remove the screws holding the cover in
place, then remove the cover.
13Disconnect all heater pipe connections
attached to the heater matrix. Be careful;
some coolant may spill.
14Lifting on the right side of the heater
matrix first, remove the heater matrix.
Refitting
Note: Always use new O-rings when attaching
the coolant lines to the heater matrix.15Refitting is the reverse of removal. Refill
the cooling system (see Chapter 1), then run
the engine with the heater on, and check for
correct operation and leaks.
12 Air conditioning system-
precautions and maintenance
1
Precautions
Warning: The air conditioning
system is under high pressure.
DO NOT loosen any hose or line
fittings, or remove any
components, until after the system has
been discharged. Air conditioning
refrigerant should be properly discharged
by a qualified refrigeration engineer. The
refrigerant used in the system must not be
allowed into contact with your skin or
eyes, or there is a risk of frostbite. Should
the refrigerant come into contact with a
naked flame, a poisonous gas will be
produced. Smoking in the presence of
refrigerant is therefore highly dangerous,
particularly if refrigerant vapour is inhaled
through a lighted cigarette. The refrigerant
is heavier than air, and it may cause
suffocation if discharged in an enclosed
space such as a domestic garage.
Finally, uncontrolled release of the
refrigerant causes environmental damage,
by contributing to the “greenhouse
effect”.
Maintenance
1The following maintenance checks should
be performed on a regular basis to ensure the
air conditioner continues to operate at peak
efficiency:
a) Check the drivebelt. If it’s worn or
deteriorated, renew it (see Chapter 1).
b) Check the system hoses. Look for cracks,
bubbles, hard spots and deterioration.
Inspect the hoses and all fittings for oil
bubbles and seepage. If there’s any
evidence of wear, damage or leaks, have
new hose(s) fitted.
c) Inspect the condenser fins for leaves, flies
and other debris. Use a “fin comb” or
compressed air to clean the condenser.
d) Make sure the system has the correct
refrigerant charge, as described below.
2It’s a good idea to operate the system for
about 10 minutes at least once a month,
particularly during the winter. Long-term non-
use can cause hardening, and subsequent
failure, of the seals.
3Because of the complexity of the air
conditioning system and the special
equipment necessary to service it, in-depth
fault diagnosis and repair procedures are not
included in this manual. However, simple
checks and component renewal procedures
are provided in this Chapter.
4The most common cause of poor cooling issimply a low system refrigerant charge. If a
noticeable loss of cool air output occurs, the
following quick check may help you determine
if the refrigerant level is low.
5Warm the engine up to normal operating
temperature.
6Set the air conditioning temperature
selector at the coldest setting, and put the
blower at the highest setting. Open the doors
(to make sure the air conditioning system
doesn’t switch off as soon as it cools the
passenger compartment).
7With the compressor engaged - the
compressor clutch will make an audible click,
and the centre of the clutch will rotate - feel
the tube located adjacent to the right front
frame rail, near the radiator.
8If a significant temperature drop is noticed,
the refrigerant level is probably OK.
9If the inlet line has frost accumulation, or
feels cooler than the receiver-drier surface,
the refrigerant charge is low. Recharging the
system should be carried out by a qualified
refrigeration engineer.
13 Air conditioning compressor
- removal and refitting
5
Warning: Due to the potential
dangers associated with the
system, you are strongly advised
to have any work on the air
conditioning system carried out by a BMW
dealer or air conditioning specialist. At the
very least, DO NOT dismantle any part of
the system (hoses, compressor, line
fittings, etc.) until after the system has
been discharged by a qualified engineer.
Refer to the precautions given at the start
of Section 12.
Note: If a new compressor is fitted, the
receiver-drier (see Section 16) should also be
renewed.
Removal
1Have the air conditioning system
discharged (see Warning above).
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.
3Disconnect the compressor clutch wiring
harness.
4Remove the drivebelt (see Chapter 1).
5Disconnect the refrigerant lines from the
rear of the compressor. Plug the open fittings
to prevent entry of dirt and moisture.
6Unbolt the compressor from the mounting
3•8 Cooling, heating and air conditioning systems