m40 BMW 3 SERIES 1988 E30 Owner's Manual

13 Sump- removal and refitting
1
1Drain the engine oil (see Chapter 1).
2Raise the front of the vehicle and place it
securely on axle stands.
3Remove the splash shields from under the
engine.
4Where applicable, disconnect the hoses
attached to the sump, and move them to one
side (see illustration).
5Where applicable, disconnect the oil level
sensor electrical connector (see illustration).
6Where applicable, remove the cast-
aluminium inspection cover that covers the
rear of the sump (see illustrations).
7On models with the M40 engine, unbolt and
remove the lower sump section and remove
the gasket (this is necessary for access to the
front mounting bolts). Unscrew the mounting
bolt, and pull the oil dipstick tube from the
sump (see illustrations). Check the condition
of the O-ring, and renew it if necessary.
8On models with the M40 engine, unscrew
the engine mounting nuts on both sides, then
attach a suitable hoist and lift the engine
sufficiently to allow the sump to be removed.
As a safety precaution, position axle stands or
blocks of wood beneath the engine.
9Remove the bolts securing the sump to theengine block and front/rear covers (see
illustration).
10Tap on the sump with a soft-faced
hammer to break the gasket seal, and lower
the sump from the engine.
11Using a gasket scraper, scrape off all
traces of the old gasket from the engine
block, the timing chain cover, the rear main oil
seal housing, and the sump. Be especially
careful not to nick or gouge the gasket sealing
surfaces of the timing chain cover and the oil
seal housing (they are made of aluminium,
and are quite soft).
12Clean the sump with solvent, and dry it
thoroughly. Check the gasket sealing surfaces
for distortion. Clean any residue from thegasket sealing surfaces on the sump and
engine with a rag dampened with a suitable
solvent.
13Before refitting the sump, apply a little
RTV-type gasket sealant to the area where the
front and rear covers join the cylinder block..
Lay a new sump gasket in place on the block.
If necessary, apply more sealant to hold the
gasket in place.
14Carefully position the sump in place (do
not disturb the gasket) and refit the bolts.
Start with the bolts closest to the centre of the
sump, and tighten them to the torque listed in
this Chapter’s Specifications, using a criss-
cross pattern. Do not overtighten them, or
leakage may occur.
In-car engine repair procedures 2A•15
13.5 If applicable, disconnect the oil level
sensor connector at the left side of the
engine, down near the power steering
pump mounting bracket13.4 If applicable, remove the nut securing
the power steering lines to the sump, and
move the lines to one side to allow you to
get at the sump bolts12.30e Angle-tightening the cylinder head
bolts (M40 engine)
13.9 Remove the bolts holding the sump
to the engine block and front cover, as
shown here on a six-cylinder engine13.7b Removing the oil dipstick tube
bracket mounting bolt
13.6b . . . remove the cover to get to all
the sump bolts13.6a Remove the four inspection cover
bolts (arrowed) and . . .
13.7a Main sump retaining bolts accessed
after removal of the lower sump section on
the M40 engine (engine on bench for clarity)
2A

15The remainder of refitting is the reverse of
removal. Fit a new gasket to the lower sump
section on models with the M40 engine.
16On completion refill the engine with oil
(Chapter 1). Run the engine and check that
there are no oil leaks from the sump gasket or
other disturbed components.
14 Oil pump- removal,
inspection and refitting
5
Removal
1Remove the sump (see Section 13).
M10, M20 and M30 engines
2On M10 and M30 engines, remove the
three bolts that attach the gear to the front of
the pump (see illustration). Note: Some
models have a single centre nut attaching the
gear to the oil pump.
3Unbolt the oil pump from the engine block
(see illustrations)and remove it.
4On the M20 engine, the intermediate shaft
drives the oil pump driveshaft, which drives
the oil pump. To remove the driveshaft,
remove the hold-down plate from the block,
and lift out the plug. Check the condition of
the O-ring, and renew it if necessary. Lift the
driveshaft out and check both gears for wear,
renewing them if worn or damaged (see
illustration).
5If the gear on the intermediate shaft is worn,
or the intermediate shaft bearing is worn or
damaged, the intermediate shaft must be
removed. Remove the engine (see Chap-
ter 2B), then remove the timing belt,
crankshaft and intermediate shaft sprockets
(see Section 10) and the engine front cover
(see Section 11). The intermediate shaft can
be slid out the front of the engine.
M40 engines
6Remove the timing belt as described in
Section 10.
7Remove the cylinder head as described in
Section 12.
8Unscrew the nut and remove the timing belt
tensioner from the front end cover (see
illustration). If necessary, unscrew the stud
from the cylinder block.9Unscrew and remove the crankshaft hub
bolt while holding the crankshaft stationary.
The bolt is tightened to a very high torque,
and it will be necessary to prevent the
crankshaft turning. Ideally, a metal bar should
be bolted to the sprocket, or the starter motor
may be removed and the flywheel held using a
wide-bladed screwdriver. Beware of possible
damage to surrounding components if it is
necessary to improvise some method of
immobilising the crankshaft.
10Remove the sprocket and spacer, noting
that the shoulder on the spacer faces inwards.
11Unscrew the bolts and remove the
stabilising and guide rollers from the front end
cover (see illustrations).12Using a small screwdriver or similar
instrument, remove the key from the groove in
the nose of the crankshaft (see illustration).
13Pull the spacer ring off the crankshaft (see
illustration).
14Unscrew the remaining bolts, and remove
the front end cover and oil pump from the
cylinder block. Note the locations of the front
cover bolts, as they are of different sizes. With
the cover removed, extract the rubber O-ring
from the groove in the nose of the crankshaft
(see illustrations).
15Note the fitted location of the oil seal, then
prise it out of the housing.
2A•16 In-car engine repair procedures
14.11b Removing the guide roller from the
front end cover (M40 engine)14.11a Removing the stabilising roller
from the front end cover (M40 engine)14.8 Removing the timing belt tensioner
(M40 engine)
14.3b On M10 and M30 engines, the oil
pump is bolted to the front and centre of
the engine block14.4 If necessary on the M20 engine,
remove the plug and oil pump driveshaft
from the engine. Inspect the driveshaft
gear, as well as this intermediate shaft
gear in the engine block (arrowed)
14.3a On M20 engines, the oil pump is
bolted across the engine block from side
to side, towards the front of the engine14.2 On M10 and M30 engines, remove the
three bolts that hold the driven gear to the
oil pump, and remove the gear

Inspection
Note:Considering that a malfunctioning oil
pump can easily cause major engine damage,
we recommend that the oil pump should
always be renewed during engine overhaul,
unless it’s in as-new condition.
M10, M20 and M30 engines
16Remove the cover and check the pump
body, gears or rotors and cover for cracks
and wear (especially in the gear or rotor
contact areas).
17Check the strainer to make sure it is not
clogged or damaged.
18Lubricate the gears with clean engine oil,
then attach the pump cover to the body and
tighten the bolts evenly and securely.19Before refitting the pump - new, rebuilt or
original - on the engine, check it for proper
operation. Fill a clean container to a depth of
one inch with fresh engine oil of the
recommended viscosity.
20Immerse the oil pump inlet in the oil, and
turn the driveshaft anti-clockwise by hand. As
the shaft is turned, oil should be discharged
from the pump outlet.M40 engines
21With the front end cover on the bench,
unscrew the bolts and remove the cover plate
to expose the oil pump rotors (see
illustrations).
22Identify the rotors for position, then
remove them from the housing (see
illustrations).23Clean the housing and the rotors
thoroughly, then refit the rotors, making sure
that they are in their previously-noted
positions. The inner rotor must be fitted with
the guide facing the body.
24Using feeler blades, measure the
clearance between the oil pump body and the
outer rotor, then check the clearance
between the outer and inner rotors (see
illustrations).
25If the clearance is not as given in the
Specifications, the complete oil pump and
front end cover should be renewed. If the
clearance is within tolerance, remove the
rotors, then pour a little engine oil into the
housing. Refit the rotors and turn them to
spread the oil around.
In-car engine repair procedures 2A•17
14.14a Front end cover and oil pump in
position on the front of the M40 engine14.13 Removing the spacer ring from the
front of the crankshaft14.12 Removing the key from the groove
in the nose of the crankshaft (M40 engine)
14.24a Measuring the clearance between
the oil pump body and the outer rotor
(M40 engine)14.22b . . . and outer rotor from the oil
pump (M40 engine)14.22a Removing the inner rotor . . .
14.21b . . . and remove the oil pump cover
(M40 engine)14.21a Unscrew the bolts . . .14.14b Extract the rubber O-ring from the
groove in the nose of the crankshaft
(M40 engine)
2A

26Refit the cover plate and tighten the bolts
to the specified torque.
27To check the pressure relief valve, extract
the circlip and remove the sleeve, spring and
piston. Check that the length of the spring is
as given in the Specifications (see
illustrations). Reassemble the pressure relief
valve using a reversal of the dismantling
procedure.
Refitting
M10, M20 and M30 engines
28Make sure the mounting surfaces are
clean, then insert the pump into the engine
block recess. Refit the bolts and tighten them
to the torque specified at the beginning of this
Chapter.
29Refitting is the reverse of removal.
M40 engines
30Clean the mating surfaces, then refit the
front end cover and oil pump to the cylinder
block, together with a new gasket (see
illustration). Tighten the bolts to the
specified torque. Note that there are two sizes
of bolts, and they have different torque
settings.
31Fit the spacer ring on the front of the
crankshaft.
32Apply engine oil to the lips of the new oil
seal, then press it into the housing to its
previously-noted position. To ensure the oil
seal enters the housing squarely, use a large
socket and the crankshaft pulley bolt to pull it
into position (see illustration).
33Refit the key to the groove in the nose of
the crankshaft.34Refit the stabilising roller to the front end
cover, and tighten the bolt.
35Refit the sprocket, spacer and crankshaft
pulley bolt. Tighten the bolt to the specified
torque while holding the crankshaft stationary
using one of the methods previously
described.
36Refit the timing belt tensioning roller, but
do not tighten the bolt at this stage.
37Refit the cylinder head as described in
Section 12.
38Refit the timing belt as described in
Section 10.
39Refit the sump (see Section 13).
15 Flywheel/driveplate-
removal and refitting
3
1Remove the transmission (on vehicles with
manual transmission, see Chapter 7A; on
vehicles with automatic transmission, see
Chapter 7B).
2On vehicles with manual transmission,
remove the clutch (see Chapter 8).
3Where necessary, mark the relationship of
the flywheel/driveplate to the crankshaft, so it
can be refitted the same way.
4The flywheel/driveplate is attached to the
rear of the crankshaft with eight bolts. Loosen
and remove the bolts, then separate it from
2A•18 In-car engine repair procedures
14.32 Using a large socket and the
crankshaft pulley bolt to pull the oil seal
into the housing (M40 engine)14.30 Locating a new gasket on the front
of the cylinder block (M40 engine)14.27e Checking the length of the
pressure relief valve spring (M40 engine)
14.27d . . . and piston14.27c . . . spring . . .
14.27b . . . and remove the sleeve . . .14.27a Extract the circlip from the oil
pump (M40 engine) . . .14.24b Measuring the clearance between
the oil pump outer and inner rotors
(M40 engine)

4Check the mountings to see if the rubber is
cracked (see illustration), hardened or
separated from the metal plates. Sometimes
the rubber will split right down the centre.
5Check for relative movement between the
mounting plates and the engine or frame (use
a large screwdriver or lever to attempt to
move the mountings). If movement is noted,
lower the engine and tighten the mounting
nuts or bolts (see illustration). Rubber
preservative should be applied to the
mountings, to slow deterioration.
6On models with the M40 engine, check the
condition of the dampers on each mounting
by disconnecting them and attempting tocompress and expand them (see illustration).
If there is very little resistance to movement,
the dampers should be renewed.
Renewal
7If the dampers on the M40 engine are to be
renewed, simply unscrew the bolts, then fit
the new dampers and tighten the bolts.
8To renew the mountings, disconnect the
battery negative cable, then raise the vehicle
and support it securely on axle stands if you
haven’t already done so.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation codebefore 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.
9Support the engine as described in
paragraph 3.
10Remove the large bracket-to-mounting
nut (see illustration). Raise the engine
slightly, then remove the lower mounting-to-
frame bolts/nuts and detach the mounting
11Refitting of the mountings is the reverse of
removal. Use thread-locking compound on
the mounting bolts/nuts, and be sure to
tighten them securely.
2A•20 In-car engine repair procedures
17.10 To remove an engine mounting, first
remove the stud nut (arrowed) -
M30 engine shown, others similar17.6 Engine mounting and damper on the
M40 engine17.5 Lever gently between the block and
the engine mounting attachment point
(arrowed) - if there is movement, tighten
the bolts

2B
General
Cylinder compression pressure (all engines) . . . . . . . . . . . . . . . . . . . . . 10 to 11 bars
Oil pressure (all engines)
At idle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5 to 2.0 bars
Running (for example, at 4000 rpm) . . . . . . . . . . . . . . . . . . . . . . . . . . 4 bars or above (typically)
Cylinder head warpage limit
Except M40 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.10 mm
M40 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.03 mm
Minimum cylinder head thickness (do not resurface the head to a thickness less than listed)
M10 and M30 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128.6 mm
M20 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124.7 mm
M40 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140.55 mm
Valves
Valve stem diameter (standard)
M10 and M30 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.0 mm
M20 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.0 mm
M40 engine
Intake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.975 mm
Exhaust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.960 mm
Minimum valve margin width
Intake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.191 mm
Exhaust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.98 mm
Valve stem maximum lateral movement (see text) . . . . . . . . . . . . . . . . . 0.787 mm
Valve face angle
Intake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45°
Exhaust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45°
Chapter 2 Part B:
General engine overhaul procedures
Compression check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Crankshaft - inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Crankshaft - refitting and main bearing oil clearance check . . . . . . . 24
Crankshaft - removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Crankshaft rear oil seal - refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Cylinder head and components - cleaning and inspection . . . . . . . 9
Cylinder head - dismantling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Cylinder head - reassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Cylinder honing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Engine - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Engine block - cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Engine block - inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Engine overhaul - alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Engine overhaul - dismantling sequence . . . . . . . . . . . . . . . . . . . . . 7Engine overhaul - general information . . . . . . . . . . . . . . . . . . . . . . . 2
Engine overhaul - reassembly sequence . . . . . . . . . . . . . . . . . . . . . 21
Engine removal - methods and precautions . . . . . . . . . . . . . . . . . . . 4
General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Initial start-up and break-in after overhaul . . . . . . . . . . . . . . . . . . . . 27
Intermediate shaft - refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Intermediate shaft - removal and inspection . . . . . . . . . . . . . . . . . . . 14
Main and connecting big-end bearings - inspection . . . . . . . . . . . . 20
Piston rings - refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Pistons/connecting rods - inspection . . . . . . . . . . . . . . . . . . . . . . . . 18
Pistons/connecting rods - refitting and big-end bearing oil
clearance check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Pistons/connecting rods - removal . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Valves - servicing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2B•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

Camshaft and rocker arms
Camshaft bearing oil clearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.033 to 0.076 mm
Camshaft endfloat
M10 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.02 to 0.13 mm
M20 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.2 mm maximum
M30 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.03 to 0.18 mm
M40 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.065 to 0.150 mm
Rocker arm radial clearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.015 to 0.051 mm
Crankshaft
Endfloat
M10 and M30 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.085 to 0.174 mm
M20 and M40 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.080 to 0.163 mm
Main bearing journal diameter (standard)
M10 engines
Red classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54.98 to 54.99 mm
Blue classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54.97 to 54.98 mm
M20 engines
Red classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59.98 to 59.99 mm
Blue classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59.97 to 59.98 mm
M30 and M40 engines
Yellow classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59.984 to 59.990 mm
Green classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59.977 to 59.983 mm
White classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59.971 to 59.976 mm
Main bearing journal diameter undersizes
1st undersize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.25 mm
2nd undersize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.50 mm
3rd undersize (where applicable) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.75 mm
Main bearing oil clearance
M10 and M20 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.030 to 0.070 mm
M30 and M40 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.020 to 0.046 mm
Connecting rod journal diameter (standard)
M10 and M30 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47.975 to 47.991 mm
M20 and M40 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44.975 to 44.991 mm
Connecting rod journal diameter undersizes
1st undersize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.25 mm
2nd undersize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.50 mm
3rd undersize (where applicable) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.75 mm
Connecting rods
Connecting rod side play (all engines) . . . . . . . . . . . . . . . . . . . . . . . . . . 0.041 mm
Connecting big-end bearing oil clearance
M10 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.030 to 0.070 mm
M20 and M30 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.020 to 0.055 mm
M40 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.010 to 0.052 mm
Engine block
Cylinder bore - diameter (standard)
M10/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89.00 to 89.01 mm
M20/B20 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80.00 to 80.01 mm
M20/B25 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84.00 to 84.01 mm
M30/B25 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86.00 to 86.01 mm
M30/B28 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86.00 to 86.01 mm
M30/B30M engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89.00 to 89.01 mm
M30/B34 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 00 to 92.01 mm
M30/B35M engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.00 to 92.01 mm
M40/B16 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84.000 to 84.014 mm
M40/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84.000 to 84.014 mm
Cylinder out-of-round limit (maximum)
M20/B20 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.02 mm
M20/B25 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.03 mm
All other engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.01 mm
Cylinder taper (maximum)
M20/B20 and M20/B25 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.02 mm
All other engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.01 mm
2B•2 General engine overhaul procedures

Pistons and piston rings
Piston diameter (standard)
M10 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88.97 mm
M20 engines
B20 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79.98 mm
B25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.98 mm
M30 engines
B30M
Alcan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88.970 mm
KS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88.980 mm
B35M
Alcan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91.972 mm
Mahle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91.980 mm
M40 engines
Factory stage 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.985 mm
Factory stage 00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84.065 mm
Piston-to-cylinder wall clearance
New
M10 and M30 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.02 to 0.05 mm
M20 and M40 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.01 to 0.04 mm
Service limit
Except B25 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.15 mm
B25 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.12 mm
Piston ring end gap
M10 engine
Top compression ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.30 to 0.70 mm
Second compression ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.20 to 0.40 mm
Oil ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.25 to 0.50 mm
M20 engine
All rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.20 to 0.50 mm
M30 engine
Top compression ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.20 to 0.45 mm
Second compression ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.40 to 0.65 mm
Oil ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.30 to 0.60 mm
M40 engine
Top compression ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.20 to 1.00 mm
Second compression ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.20 to 1.00 mm
Oil ring
B16 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.20 to 1.00 mm
B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.40 to 1.40 mm
Piston ring side clearance
M10 engine
Top compression ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.06 to 0.09 mm
Second compression ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.03 to 0.072 mm
Oil ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.02 to 0.06 mm
M20 engine
Top compression ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.04 to 0.08 mm
Second compression ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.03 to 0.07 mm
Oil ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.02 to 0.05 mm
M30 engine
Top compression ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.04 to 0.072 mm
Second compression ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.03 to 0.062 mm
Oil ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.02 to 0.055 mm
M40 engine
Top compression ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.02 to 0.20 mm
Second compression ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.02 to 0.10 mm
Oil ring
B16 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.02 to 0.10 mm
B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Not measured
Torque wrench settingsNm
Main bearing cap-to-engine block bolts*
M10, M20 and M30 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
M40 engines
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Angle-tighten an additional 50°
General engine overhaul procedures 2B•3
2B

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