1990 BMW 5 SERIES engine

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)

the crankshaft flange (see illustration). Be
careful - the flywheel is heavy.
5To refit the flywheel/driveplate on the
crankshaft, use a liquid thread-locking
compound on the bolts, and tighten them
gradually, using a criss-cross pattern, to the
torque listed in this Chapter’s Specifications.
6The remainder of refitting is the reverse of
removal.
16 Crankshaft rear oil seal-
renewal
3
1Remove the flywheel or driveplate (see
Section 15).
2Remove the bolts and/or nuts attaching the
seal retainer to the engine block. Be sure to
remove the two bolts (from underneath)
connecting the rear of the sump to the bottom
of the seal retainer (see illustration).
3Run a sharp, thin knife between the sump
gasket and the seal retainer, cutting the
retainer free from the gasket. Be very careful
not to damage the gasket, and keep it clean
so you can re-use it.
4Break the seal retainer-to-block gasket seal
by tapping the retainer with a plastic mallet or
block of wood and hammer. Do not prise
between the retainer and the engine block, as
damage to the gasket sealing surfaces will
result.
5Using a scraper, remove all traces of old
gasket material from the sealing surfaces of
the retainer and engine block. Gasket removal
solvents are available at car accessory shops,
and may prove helpful. After all gasket
material has been removed, the gasket
surfaces can be degreased by wiping them
with a rag dampened with a suitable solvent.
Caution: Be very careful not to
scratch or gouge the delicate
aluminium surfaces. Also, do not
damage the sump gasket, and
keep it clean.
6Support the retainer on two blocks of
wood, and drive out the seal from behind with
a hammer and screwdriver (see illustration).Be very careful not to damage the seal bore in
the process.
7Coat the outside diameter and lip of the
new seal with multi-purpose grease, and drive
the seal into the retainer with a hammer and a
block of wood (see illustration).
8Apply a film of RTV-type gasket sealant to
the surface of the sump gasket that mates with
the seal retainer. Apply extra beads of RTV
sealant to the edges where the gasket meets
the engine block. Note:If the sump gasket is
damaged, instead of fitting a whole new
gasket, you might try trimming the rear portion
of the gasket off at the point where it meets the
engine block, then trim off the rear portion of a
new sump gasket so it’s exactly the same size.
Cover the exposed inside area of the sump
with a rag, then clean all traces of old gasket
material off the area where the gasket was
removed. Attach the new gasket piece to the
sump with contact-cement-type gasket
adhesive, then apply RTV-type sealant as
described at the beginning of this paragraph.
9Coat both sides of the new retainer gasket
with RTV-type gasket sealant, then attach the
gasket to the seal retainer. Fit the seal retainer
to the rear of the engine, then refit the bolts
and tighten them evenly to the torque listed in
this Chapter’s Specifications. Work from bolt-
to-bolt in a criss-cross pattern to be sure
they’re tightened evenly.Note 1:Tighten the
retainer-to-block bolts first, then tighten the
sump-to-retainer bolts.Note 2:After applying
RTV-type sealant, reassembly must becompleted in about 10 minutes so the RTV
won’t prematurely harden.
10Refit the flywheel/driveplate (see Sec-
tion 15).
11Refit the transmission (on vehicles with
manual transmission, see Chapter 7A; on
vehicles with automatic transmission, see
Chapter 7B).
17 Engine mountings-
check and renewal
1
1Engine mountings seldom require attention,
but broken or deteriorated mountings should
be renewed immediately, or the added strain
placed on the driveline components may
cause damage or wear.
Check
2During the check, the engine must be
raised slightly to remove its weight from the
mounts.
3Raise the vehicle and support it securely on
axle stands, then position a jack under the
engine sump. Place a large block of wood
between the jack head and the sump, then
carefully raise the engine just enough to take
its weight off the mounts.
Warning: DO NOT place any part
of your body under the engine
when it’s supported only by a
jack!
In-car engine repair procedures 2A•19
16.6 After removing the retainer from the
block, support it on two wood blocks, and
drive out the old seal with a punch and
hammer16.2 Remove the six bolts from the rear of
the block and the two from underneath at
the sump15.4 Using a socket and ratchet, remove
the eight bolts that hold the flywheel/
driveplate to the crankshaft flange - prevent
the flywheel/driveplate from turning by
locking the ring gear with a lever
17.4 As engine mountings wear or age,
they should be inspected for cracking or
separation from their metal plates
16.7 Drive the new seal into the retainer
with a block of wood, or a section of pipe,
if you have one large enough - make sure
the seal enters the retainer bore squarely
2A

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