ECO BMW 3 SERIES 1983 E30 Owner's Guide

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

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

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

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

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

carbon deposits or cylinder wear have
produced ridges, they must be completely
removed with a special tool called a ridge
reamer (see illustration). Follow the
manufacturer’s instructions provided with the
tool. Failure to remove the ridges before
attempting to remove the piston/connecting
rod assemblies may result in piston ring
breakage.
2After the cylinder ridges have been
removed, turn the engine upside-down so the
crankshaft is facing up.
3Before the connecting rods are removed,
check the side play with feeler gauges. Slide
them between the first connecting rod and
crankshaft web until no play is apparent (see
illustration). The side play is equal to the
thickness of the feeler gauge(s). If the side
play exceeds the service limit, new
connecting rods will be required. If new rods
(or a new crankshaft) are fitted, ensure that
some side play is retained (if not, the rods will
have to be machined to restore it - consult a
machine shop for advice if necessary). Repeat
the procedure for the remaining connecting
rods.
4Check the connecting rods and caps for
identification marks. If they aren’t plainly
marked, use a small centre-punch to make
the appropriate number of indentations (see
illustration)on each rod and cap (1, 2, 3, etc.,
depending on the cylinder they’re associated
with).
5Loosen each of the connecting rod cap
nuts/bolts a half-turn at a time until they can
be removed by hand. Remove the No 1
connecting rod cap and bearing shell. Don’t
drop the bearing shell out of the cap.
6Where applicable, slip a short length of
plastic or rubber hose over each connecting
rod cap stud to protect the crankshaft journal
and cylinder wall as the piston is removed
(see illustration).
7Remove the bearing shell, and push the
connecting rod/piston assembly out through
the top of the engine. Use a wooden hammer
handle to push on the upper bearing surface
in the connecting rod. If resistance is felt,
double-check to make sure that all of the
ridge was removed from the cylinder.8Repeat the procedure for the remaining
cylinders.
9After removal, reassemble the connecting
rod caps and bearing shells in their respective
connecting rods, and refit the cap nuts/bolts
finger-tight. Leaving the old bearing shells in
place until reassembly will help prevent the
connecting big-end bearing surfaces from
being accidentally nicked or gouged.
10Don’t separate the pistons from the
connecting rods (see Section 18).
13 Crankshaft- removal
5
Note: The crankshaft can be removed only
after the engine has been removed from the
vehicle. It’s assumed that the flywheel or
driveplate, vibration damper, timing chain or
belt, sump, oil pump and piston/connecting
rod assemblies have already been removed.
The rear main oil seal housing must be
unbolted and separated from the block before
proceeding with crankshaft removal.
1Before the crankshaft is removed, check
the endfloat. Mount a dial indicator with the
stem in line with the crankshaft and touching
the nose of the crankshaft, or one of its webs
(see illustration).
2Push the crankshaft all the way to the rear,and zero the dial indicator. Next, prise the
crankshaft to the front as far as possible, and
check the reading on the dial indicator. The
distance that it moves is the endfloat. If it’s
greater than the maximum endfloat listed in
this Chapter’s Specifications, check the
crankshaft thrust surfaces for wear. If no wear
is evident, new main bearings should correct
the endfloat.
3If a dial indicator isn’t available, feeler
gauges can be used. Identify the main bearing
with the thrust flanges either side of it - this is
referred to as the “thrust” main bearing (see
Section 24, paragraph 6). Gently prise or push
the crankshaft all the way to the front of the
engine. Slip feeler gauges between the
crankshaft and the front face of the thrust
main bearing to determine the clearance.
4Check the main bearing caps to see if
they’re marked to indicate their locations.
They should be numbered consecutively from
the front of the engine to the rear. If they
aren’t, mark them with number-stamping dies
or a centre-punch (see illustration). Main
bearing caps generally have a cast-in arrow,
which points to the front of the engine.
Loosen the main bearing cap bolts a quarter-
turn at a time each, working from the outer
ends towards the centre, until they can be
removed by hand. Note if any stud bolts are
used, and make sure they’re returned to their
original locations when the crankshaft is
refitted.
General engine overhaul procedures 2B•13
12.4 Mark the big-end bearing caps in
order from the front of the engine to the
rear (one mark for the front cap, two for
the second one and so on)12.3 Check the connecting rod side play
with a feeler gauge as shown12.1 A ridge reamer is required to remove
the ridge from the top of each cylinder - do
this before removing the pistons!
13.1 Checking crankshaft endfloat with a
dial indicator
12.6 To prevent damage to the crankshaft
journals and cylinder walls, slip sections of
rubber or plastic hose over the rod bolts
before removing the pistons
2B

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

12Check the piston-to-rod clearance by
twisting the piston and rod in opposite
directions. Any noticeable play indicates
excessive wear, which must be corrected. The
piston/connecting rod assemblies should be
taken to a machine shop for attention.
13If the pistons must be removed from the
connecting rods for any reason, they should
be taken to a machine shop. When this is
done, have the connecting rods checked for
bend and twist, since most machine shops
have special equipment for this purpose.
Note:Unless new pistons and/or connecting
rods must be fitted, do not dismantle the
pistons and connecting rods.
14Check the connecting rods for cracks and
other damage. Temporarily remove the rod
caps, lift out the old bearing shells, wipe the rod
and cap bearing surfaces clean, and inspect
them for nicks, gouges and scratches. After
checking the rods, fit new bearing shells, slip the
caps into place, and tighten the nuts finger-tight.
19 Crankshaft- inspection
3
1Remove all burrs from the crankshaft oil
holes with a stone, file or scraper (see
illustration).2Clean the crankshaft with solvent, and dry it
with compressed air (if available). Be sure to
clean the oil holes with a stiff brush (see
illustration), and flush them with solvent.
3Check the main and connecting big-end
bearing journals for uneven wear, scoring, pits
and cracks.
4Rub a copper coin across each journal
several times (see illustration). If a journal
picks up copper from the coin, it’s too rough
and must be reground.
5Check the rest of the crankshaft for cracks
and other damage. If necessary, have a
machine shop inspect the crankshaft.
6Using a micrometer, measure the diameter
of the main and connecting rod journals, and
compare the results to this Chapter’s Specifi-
cations (see illustration). By measuring the
diameter at a number of points around each
journal’s circumference, you’ll be able to
determine whether or not the journal is out-of-
round. Take the measurement at each end of
the journal, near the crank webs, to determine
if the journal is tapered.
7If the crankshaft journals are damaged,
tapered, out-of-round or worn beyond the
limits given in the Specifications, have the
crankshaft reground by a machine shop. Be
sure to use the correct-size bearing shells if
the crankshaft is reconditioned.
8Check the oil seal journals at each end ofthe crankshaft for wear and damage. If the
seal has worn a groove in the journal, or if it’s
nicked or scratched (see illustration), the
new seal may leak when the engine is
reassembled. In some cases, a machine shop
may be able to repair the journal by pressing
on a thin sleeve. If repair isn’t feasible, a new
or different crankshaft should be fitted.
9Examine the main and big-end bearing
shells (see Section 20).
20 Main and connecting
big-end bearings- inspection
3
1Even though the main and connecting big-
end bearings should be renewed during the
engine overhaul, the old bearings should be
retained for close examination, as they may
reveal valuable information about the
condition of the engine (see illustration).
2Bearing failure occurs because of lack of
lubrication, the presence of dirt or other
foreign particles, overloading the engine, and
corrosion. Regardless of the cause of bearing
failure, it must be corrected before the engine
is reassembled, to prevent it from happening
again.
General engine overhaul procedures 2B•17
19.4 Rubbing a penny lengthways on each
journal will reveal its condition - if copper
rubs off and is embedded in the crankshaft,
the journals should be reground19.2 Use a wire or stiff plastic bristle
brush to clean the oil passages in the
crankshaft19.1 The oil holes should be chamfered so
sharp edges don’t gouge or scratch the
new bearings
20.1 Typical bearing failures
A Scratched by dirt: debris embedded into
bearing material
B Lack of oil: overlay wiped out
C Improper seating: bright (polished) sections
D Tapered journal: overlay gone from entire
surface
E Radius ride
F Fatigue failure: craters or pockets
19.8 If the seals have worn grooves in the
crankshaft journals, or if the seal contact
surfaces are nicked or scratched, the new
seals will leak19.6 Measure the diameter of each
crankshaft journal at several points to
detect taper and out-of-round conditions
2B

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