air intake BMW 3 SERIES 1985 E30 User Guide

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

detach them. Pieces of masking tape with
numbers or letters written on them work well
(see illustration).
6Label and detach all coolant hoses from the
engine (see Chapter 3).
7Remove the cooling fan, shroud and
radiator (see Chapter 3). Note:On the M40
engine, it is only necessary to remove the
cooling fan and shroud; however, prevent
damage to the radiator by covering it with a
piece of wood or cardboard.
8Remove the drivebelts (see Chapter 1).
9Disconnect the fuel lines from the fuel rail
(see Chapter 4).
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area, and don’t work
in a garage where a natural gas-type
appliance (such as a water heater or
clothes dryer) with a pilot light is present.
If you spill any fuel on your skin, rinse it off
immediately with soap and water. When
you perform any kind of work on the fuel
system, wear safety glasses, and have a
fire extinguisher on hand.
10Disconnect the accelerator cable (see
Chapter 4) and kickdown linkage/speed
control cable (see Chapter 7B), if applicable,
from the engine.
11Where fitted, unbolt the power steering
pump (see Chapter 10). Leave the lines/hoses
attached, and make sure the pump is kept in
an upright position in the engine compartment
(use wire or rope to restrain it out of the way).
12On air-conditioned models, unbolt the
compressor (see Chapter 3) and set it aside,
or tie it up out of the way. Do not disconnect
the hoses.
13Drain the engine oil (see Chapter 1) and
remove the filter. Remove the engine splash
guard from under the engine.
14Remove the starter motor (see Chapter 5).15Remove the alternator (see Chapter 5).
This is not essential on all models, but it is a
good idea in any case to avoid accidental
damage.
16Unbolt the exhaust system from the
engine (see Chapter 4).
17If you’re working on a vehicle with an
automatic transmission, remove the torque
converter-to-driveplate fasteners (see
Chapter 7B). On the M40 engine, unbolt the
automatic transmission fluid coolant pipes
from the sump.
18Support the transmission with a jack.
Position a block of wood between them, to
prevent damage to the transmission. Special
transmission jacks with safety chains are
available - use one if possible.
19Attach an engine sling or a length of chain
to the lifting brackets on the engine. If the
brackets have been removed, the chain can
be bolted directly to the intake manifold studs,
but place a flat washer between the chain and
the nut, and tighten the nut all the way up to
the chain, to avoid the possibility of the studs
bending.
20Roll the hoist into position and connect
the sling to it. Take up the slack in the sling or
chain, but don’t lift the engine.
Warning: DO NOT place any part
of your body under the engine
when it’s supported only by a
hoist or other lifting device.
21On M10, M20 and M30 engines, remove
the transmission rear crossmember, and
slightly lower the rear of the transmission.
22Remove the transmission-to-engine block
bolts using a Torx socket. Note:The bolts
holding the bellhousing to the engine block
will require a swivel at the socket, and a very
long extension going back towards the
transmission.
23Remove the engine mounting-to-frame
bracket nuts. On the M40 engine, unbolt the
dampers from the mountings.
24Recheck to be sure nothing is still
connecting the engine to the transmission or
vehicle. Disconnect anything still remaining.
25Raise the engine slightly. Carefully work it
forwards to separate it from the transmission.
If you’re working on a vehicle with an
automatic transmission, you may find the
torque converter comes forward with theengine. If it stays with the transmission, leave
it, but you may find it easier to let it come
forward until it can be grasped easier and be
pulled from the crankshaft. Note:When
refitting the torque converter to the
transmission before the engine is refitted, be
sure to renew the transmission front pump
seal, which will probably be damaged when
the converter comes out with the engine.
Either method is acceptable, but be prepared
for some fluid to leak from the torque
converter if it comes out of the transmission. If
you’re working on a vehicle with a manual
transmission, draw the engine forwards until
the input shaft is completely disengaged from
the clutch. Slowly raise the engine out of the
engine compartment. Check carefully to make
sure everything is disconnected.
26Remove the flywheel/driveplate (and
where applicable, the engine rear plate), and
mount the engine on an engine stand (see
illustration). Do not turn the M40 engine
upside-down (see Cautionin Section 4).
Refitting
27Check the engine and transmission
mountings. If they’re worn or damaged, renew
them.
28Refit the flywheel or driveplate (see
Chapter 2A). If you’re working on a manual
transmission vehicle, refit the clutch and
pressure plate (see Chapter 7A). Now is a
good time to fit a new clutch.
29If the torque converter came out with the
engine during removal, carefully refit the
converter into the transmission before the
engine is lowered into the vehicle.
30Carefully lower the engine into the engine
compartment - make sure the engine
mountings line up.
31If you’re working on an automatic
transmission vehicle, guide the torque
converter onto the crankshaft following the
procedure outlined in Chapter 7B.
32If you’re working on a manual
transmission vehicle, apply a dab of high-
melting-point grease to the input shaft, and
guide it into the clutch and crankshaft pilot
bearing until the bellhousing is flush with the
engine block.. Do not allow the weight of the
engine to hang on the input shaft.
33Refit the transmission-to-engine bolts,
and tighten them securely.
Caution: DO NOT use the bolts to
force the transmission and
engine together.
34Refit the remaining components in the
reverse order of removal.
35Add coolant, oil, power steering and
transmission fluid as needed.
2B•6 General engine overhaul procedures
5.26 Removing the engine rear plate -
M40 engine5.5 Label each wire before unplugging the
connector
If there’s any possibility of
confusion, make a sketch of
the engine compartment and
clearly label the lines, hoses
and wires.
It may be necessary to rock
the engine slightly, or to turn
the crankshaft, to allow the
input shaft splines to mate
with the clutch plate

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

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

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

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).

Carburettor (Solex 2BE)
Main jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X120
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X110
Air correction jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Venturi diameter
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 mm
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 mm
Idle fuel jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47.5 mm
Idle air jet
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
Float needle valve diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 mm
Throttle positioner coil resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.97 to 1.63 ohms
Intake air temperature resistance
-10º C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8200 to 10 500 ohms
20º C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2200 to 2700 ohms
80º C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 to 360 ohms
Float level
Stage 1 float chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27.0 to 29.0 mm
Stage 2 float chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29.0 to 31.0 mm
Fuel pressure checks (carburettor engines)
Fuel pump delivery pressure (engine idling) . . . . . . . . . . . . . . . . . . . . . . 0.1 to 0.3 bars
Fuel pressure checks (fuel injection engines)
Fuel system pressure (relative to intake manifold pressure)
3-Series (E30)
316i with M40/B16 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 ± 0.06 bars
318i with M10/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 to 3.0 bars
318i with M40/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 ± 0.06 bars
320i with M20/B20 engine (L-Jetronic) . . . . . . . . . . . . . . . . . . . . . . 2.5 to 3.0 bars
320i with M20/B20 engine (Motronic) . . . . . . . . . . . . . . . . . . . . . . . 2.5 ± 0.05 bars
325i with M20/B25 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 ± 0.05 bars
5-Series (E28/”old-shape”)
All models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 to 3.0 bars
5-Series (E34/”new-shape”)
518i with M40/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 ± 0.06 bars
All other models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 to 3.0 bars
Fuel system hold pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 bars
Fuel pump maximum pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 to 6.9 bars
Fuel pump hold pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 bars
Transfer pump pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.28 to 0.35 bars
Injectors
Injector resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.5 to 17.5 ohms
Accelerator cable free play . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.0 mm
Torque wrench settingsNm
Carburettor mountings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Fuel pump to cylinder head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Throttle body nuts/bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 to 26
4•2 Fuel and exhaust systems
1 General information
With the exception of early models (316 and
518 models) all engines are equipped with
electronic fuel injection.
Early 316 and 518 models are equipped
with Solex carburettors. The carburettor fitted
is either a Solex 2B4 (early models) or
2BE (later models). The mechanical fuel pumpis driven by an eccentric lobe on the
camshaft.
Fuel injection models are equipped with
either the L-Jetronic or the Motronic fuel
injection system. From 1988, fuel injection
models are equipped with an updated version
of the Motronic system - this system is easily
distinguished from the earlier system by the
absence of a cold start injector. The electric
fuel pump is located beneath the rear of the
vehicle, or inside the fuel tank. The fuel pump
relay on Motronic systems is activated from aearth signal from the Motronic control unit
(ECU). The fuel pump operates for a few
seconds when the ignition is first switched on,
and it continues to operate only when the
engine is actually running.Air intake system
The air intake system consists of the air
filter housing, the airflow meter and throttle
body (fuel injection models), and the intake
manifold. All components except the intake
manifold are covered in this Chapter; for

information on removing and refitting the
intake manifold, refer to Chapter 2A.
The throttle valve inside the throttle body or
carburettor is actuated by the accelerator
cable. When you depress the accelerator
pedal, the throttle plate opens and airflow
through the intake system increases.
On fuel injection systems, a flap inside the
airflow meter opens wider as the airflow
increases. A throttle position switch attached
to the pivot shaft of the flap detects the angle
of the flap (how much it’s open) and converts
this to a voltage signal, which it sends to the
computer.
Fuel system
On carburettor models, the fuel pump
supplies fuel under pressure to the
carburettor. A needle valve in the float
chamber maintains the fuel at a constant
level. A fuel return system channels excess
fuel back to the fuel tank.
On fuel injection models, an electric fuel
pump supplies fuel under constant pressure
to the fuel rail, which distributes fuel to the
injectors. The electric fuel pump is located
inside the fuel tank on later models, or beside
the fuel tank on early models. Early models
also have a transfer pump located in the fuel
tank. The transfer pump acts as an aid to the
larger main pump for delivering the necessary
pressure. A fuel pressure regulator controls
the pressure in the fuel system. The fuel
system also has a fuel pulsation damper
located near the fuel filter. The damper
reduces the pressure pulsations caused by
fuel pump operation, and the opening and
closing of the injectors. The amount of fuel
injected into the intake ports is precisely
controlled by an Electronic Control Unit (ECU
or computer). Some later 5-Series models
have a fuel cooler in the return line.
Electronic control system (fuel
injection system)
Besides altering the injector opening
duration as described above, the electronic
control unit performs a number of other tasks
related to fuel and emissions control. It
accomplishes these tasks by using data
relayed to it by a wide array of information
sensors located throughout the enginecompartment, comparing this information to
its stored map, and altering engine operation
by controlling a number of different actuators.
Since special equipment is required, most
fault diagnosis and repair of the electronic
control system is beyond the scope of the
home mechanic. Additional information and
testing procedures for the emissions system
components (oxygen sensor, coolant
temperature sensor, EVAP system, etc.) is
contained in Chapter 6.
2 Fuel injection system-
depressurising
1
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke or allow open flames or bare light
bulbs near the work area. Also, don’t work
in a garage where a natural gas-type
appliance with a pilot light is present.
1Remove the fuel pump fuse from the main
fuse panel (see illustrations). Note:Consult
your owner’s handbook for the exact location
of the fuel pump fuse, if the information is not
stamped onto the fusebox cover.
2Start the engine, and wait for it to stall.
Switch off the ignition.
3Remove the fuel filler cap to relieve the fuel
tank pressure.
4The fuel system is now depressurised.
Note:Place a rag around fuel lines before
disconnecting, to prevent any residual fuel
from spilling onto the engine(see
illustration).
5Disconnect the battery negative cable
before working on any part of the system.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
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.
3 Fuel pump/fuel pressure-
check
3
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Also, don’t work
in a garage where a natural gas-type
appliance with a pilot light is present.
Carburettor engines
1To test the fuel pump, it will be necessary to
connect a suitable pressure gauge between
the fuel pump outlet, and the carburettor
supply pipe. For this particular test, the fuel
return valve, which is normally connected in
the fuel line from the fuel pump to the
carburettor, mustbe bypassed.
2With the engine running at idle speed, the
pump pressure should be between 0.1 and
0.3 bars.
3Should a pressure gauge not be available, a
simpler (but less accurate) method of testing
the fuel pump is as follows.
4Disconnect the outlet hose from the fuel
pump.
5Disconnect the LT lead from the coil, to
prevent the engine firing, then turn the engine
over on the starter. Well-defined spurts of fuel
should be ejected from the outlet hose.
Fuel injection engines
Note 1:The electric fuel pump is located
inside the fuel tank on later models, or beside
the fuel tank on early models. Early models are
also equipped with a transfer pump located in
the fuel tank. The transfer pump feeds the
main pump, but can’t generate the high
pressure required by the system.
Note 2:The fuel pump relay on Motronic
systems is activated by an earth signal from
the Motronic control unit (ECU). The fuel
pump operates for a few seconds when the
ignition is first switched on, and then
continues to operate only when the engine is
actually running.
Fuel and exhaust systems 4•3
2.4 Be sure to place a rag under and
around any fuel line when disconnecting2.1b Removing the fuel pump fuse on
5-Series models2.1a Removing the fuel pump fuse on
3-Series models
4

6Unscrew the four nuts retaining the air
cleaner to the carburettor, and remove the
metal ring (see illustrations).
7Unscrew the nut from the mounting bracket
(see illustration).
8Lift the air cleaner from the carburettor, and
disconnect the crankcase ventilation hose
(see illustration). If necessary, prise the
sealing ring from the bottom of the air cleaner.
9Refitting is a reversal of removal, but align
the arrow on the cover with the arrow on the
inlet tube (see illustration).
Fuel injection engines
10Detach the air intake duct from the front
side of the air cleaner.11Detach the duct between the air cleaner
and the throttle body.
12Remove the air filter (see Chapter 1).
13Unplug the electrical connector from the
airflow meter (see Section 12).
14Remove the air cleaner mounting bolts
(see illustration)and lift the air cleaner
assembly from the engine compartment.
15Refitting is the reverse of removal. Ensure
that all ducts are securely refitted, or air leaks
will result.
9 Accelerator cable- check,
adjustment and renewal
1
Check
1Separate the air intake duct from the
throttle body (fuel injection models) or remove
the air cleaner (carburettor models).
2Have an assistant depress the accelerator
pedal to the floor while you watch the throttle
valve. It should move to the fully-open
position.
3Release the accelerator pedal, and make
sure the throttle valve returns smoothly to the
fully-closed position. The throttle valve should
not contact the body at any time during its
movement; if it does, the unit must be renewed.
Adjustment
4Warm the engine to normal operating
temperature, then switch it off. Depress theaccelerator pedal to the floor twice, then
check the cable free play at the
carburettor/throttle body. Compare it to the
value listed in this Chapter’s Specifications.
5If the free play isn’t as specified, adjust it by
turning the adjustment nut (see illustration).
6Have an assistant help you verify the
throttle valve is fully open when the
accelerator pedal is depressed to the floor.
Renewal
Note:The following paragraphs describe the
procedure for fuel injection engines - the
procedure is similar on carburettor engines
7Disconnect the battery negative cable.
Fuel and exhaust systems 4•9
8.6b . . . and remove the metal ring8.6a Unscrew the four air cleaner-to-
carburettor nuts . . .8.4 Air cleaner inlet duct (1) and warm-air
hose (2)
9.5 To adjust the accelerator cable free
play, hold nut B stationary and turn nut A
(fuel injection engine shown)8.14 Remove the two nuts (arrowed) from
the air cleaner assembly (Motronic system
shown), and lift it off its mountings
8.8 Disconnecting the crankcase
ventilation hose from the air cleaner8.7 Air cleaner mounting bracket nut
(arrowed)8.9 Align the air cleaner cover arrows
when refitting
4