1991 BMW 5 SERIES final drive

0•4Introduction
The E30 3-Series range first became
available in the UK in March 1983, and
continued in production until April 1991, when
the revised E36 3-Series range (not covered
by this manual) was introduced. Convertible
and Touring (Estate) models were introduced
for 1988, and these models have continued in
E30 form to date.
The E28 5-Series models were introduced
in October 1981, and were superseded in
June 1988 by the revised E34 5-Series range,
Touring versions of which became available
from March 1992. Throughout this manual,
E28 models are also referred to as “old-
shape”, while E34 models are designated
“new-shape”.
The models covered by this manual are
equipped with single overhead cam in-line
four- and six-cylinder engines. Early 316 and
518 models are fitted with carburettors, but all
other models are fitted with fuel injection
systems. Transmissions are a five-speed
manual, or three- or four-speed automatic.
The transmission is mounted to the back of
the engine, and power is transmitted to the
fully-independent rear axle through a two-
piece propeller shaft. The final drive unit is
bolted solidly to a frame crossmember, and
drives the rear wheels through driveshaftsequipped with inner and outer constant
velocity joints.
The front suspension is of MacPherson
strut type, with the coil spring/shock absorber
unit making up the upper suspension link. The
rear suspension is made up of coil spring-
over-shock absorber struts, or coil springs
and conventional shock absorbers,
depending on model.
The brakes are disc type at the front, with
either drums or discs at the rear, depending
on model. Servo assistance is standard on all
models. Some later models are equipped with
an Anti-lock Braking System (ABS).
All models are manufactured to fine limits,
and live up to the BMW reputation of quality
workmanship. Although many of the models
covered by this manual appear complex at
first sight, they should present no problems to
the home mechanic.
Note for UK readers
The greater part of this manual was
originally written in the USA. Some of the
photographs used are of American-market
models, but the procedures given are fully
applicable to right-hand-drive models (or have
been amended where necessary).
Acknowledgements
Thanks are due to Champion Spark Plug,
who supplied the illustrations showing spark
plug conditions. Thanks are also due to
Sykes-Pickavant Limited, who provided some
of the workshop tools, and to all those people
at Sparkford who helped in the production of
this manual. Technical writers who
contributed to this project include Robert
Maddox, Mark Ryan and Mike Stubblefield.
We take great pride in the accuracy of
information given in this manual, but
vehicle manufacturers make alterations
and design changes during the production
run of a particular vehicle of which they do
not inform us. No liability can be accepted
by the authors or publishers for loss,
damage or injury caused by any
errors in, or omissions from, the
information given.
Project vehicles
The main project vehicle used in the
preparation of this manual for the UK market
was a 1988 BMW 318i with an M40/B18
engine.
Introduction to the BMW 3- and 5-Series
BMW 320i Saloon (E30)

0•6Safety First!
Working on your car can be dangerous.
This page shows just some of the potential
risks and hazards, with the aim of creating a
safety-conscious attitude.
General hazards
Scalding
• Don’t remove the radiator or expansion
tank cap while the engine is hot.
• Engine oil, automatic transmission fluid or
power steering fluid may also be dangerously
hot if the engine has recently been running.
Burning
• Beware of burns from the exhaust system
and from any part of the engine. Brake discs
and drums can also be extremely hot
immediately after use.
Crushing
• When working under or near
a raised vehicle,
always
supplement the
jack with axle
stands, or use
drive-on
ramps.
Never
venture
under a car which
is only supported by a jack.
• Take care if loosening or tightening high-
torque nuts when the vehicle is on stands.
Initial loosening and final tightening should
be done with the wheels on the ground.
Fire
• Fuel is highly flammable; fuel vapour is
explosive.
• Don’t let fuel spill onto a hot engine.
• Do not smoke or allow naked lights
(including pilot lights) anywhere near a
vehicle being worked on. Also beware of
creating sparks
(electrically or by use of tools).
• Fuel vapour is heavier than air, so don’t
work on the fuel system with the vehicle over
an inspection pit.
• Another cause of fire is an electrical
overload or short-circuit. Take care when
repairing or modifying the vehicle wiring.
• Keep a fire extinguisher handy, of a type
suitable for use on fuel and electrical fires.
Electric shock
• Ignition HT
voltage can be
dangerous,
especially to
people with heart
problems or a
pacemaker. Don’t
work on or near the
ignition system with
the engine running or
the ignition switched on.• Mains voltage is also dangerous. Make
sure that any mains-operated equipment is
correctly earthed. Mains power points should
be protected by a residual current device
(RCD) circuit breaker.
Fume or gas intoxication
• Exhaust fumes are
poisonous; they often
contain carbon
monoxide, which is
rapidly fatal if inhaled.
Never run the
engine in a
confined space
such as a garage
with the doors shut.
• Fuel vapour is also
poisonous, as are the vapours from some
cleaning solvents and paint thinners.
Poisonous or irritant substances
• Avoid skin contact with battery acid and
with any fuel, fluid or lubricant, especially
antifreeze, brake hydraulic fluid and Diesel
fuel. Don’t syphon them by mouth. If such a
substance is swallowed or gets into the eyes,
seek medical advice.
• Prolonged contact with used engine oil can
cause skin cancer. Wear gloves or use a
barrier cream if necessary. Change out of oil-
soaked clothes and do not keep oily rags in
your pocket.
• Air conditioning refrigerant forms a
poisonous gas if exposed to a naked flame
(including a cigarette). It can also cause skin
burns on contact.
Asbestos
• Asbestos dust can cause cancer if inhaled
or swallowed. Asbestos may be found in
gaskets and in brake and clutch linings.
When dealing with such components it is
safest to assume that they contain asbestos.
Special hazards
Hydrofluoric acid
• This extremely corrosive acid is formed
when certain types of synthetic rubber, found
in some O-rings, oil seals, fuel hoses etc, are
exposed to temperatures above 400
0C. The
rubber changes into a charred or sticky
substance containing the acid. Once formed,
the acid remains dangerous for years. If it
gets onto the skin, it may be necessary to
amputate the limb concerned.
• When dealing with a vehicle which has
suffered a fire, or with components salvaged
from such a vehicle, wear protective gloves
and discard them after use.
The battery
• Batteries contain sulphuric acid, which
attacks clothing, eyes and skin. Take care
when topping-up or carrying the battery.
• The hydrogen gas given off by the battery
is highly explosive. Never cause a spark or
allow a naked light nearby. Be careful when
connecting and disconnecting battery
chargers or jump leads.
Air bags
• Air bags can cause injury if they go off
accidentally. Take care when removing the
steering wheel and/or facia. Special storage
instructions may apply.
Diesel injection equipment
• Diesel injection pumps supply fuel at very
high pressure. Take care when working on
the fuel injectors and fuel pipes.
Warning: Never expose the hands,
face or any other part of the body
to injector spray; the fuel can
penetrate the skin with potentially fatal
results.
Remember...
DO
• Do use eye protection when using power
tools, and when working under the vehicle.
• Do wear gloves or use barrier cream to
protect your hands when necessary.
• Do get someone to check periodically
that all is well when working alone on the
vehicle.
• Do keep loose clothing and long hair well
out of the way of moving mechanical parts.
• Do remove rings, wristwatch etc, before
working on the vehicle – especially the
electrical system.
• Do ensure that any lifting or jacking
equipment has a safe working load rating
adequate for the job.
A few tips
DON’T
• Don’t attempt to lift a heavy component
which may be beyond your capability – get
assistance.
• Don’t rush to finish a job, or take
unverified short cuts.
• Don’t use ill-fitting tools which may slip
and cause injury.
• Don’t leave tools or parts lying around
where someone can trip over them. Mop
up oil and fuel spills at once.
• Don’t allow children or pets to play in or
near a vehicle being worked on.

Tyre pressures (cold) - bars (psi)Front Rear
3-Series, E30
316 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.9 (28) 2.1 (30)
316i
Saloon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 (29) 2.1 (30)
Estate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 (29) 2.2 (32)
318i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8 (26) 1.9 (28)
320i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.9 (28) 2.0 (29)
325i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 (32) 2.3 (33)
5-Series, E28 (“old-shape”)
518 and 518i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 (29) 2.0 (29)
525i and 528i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 (32) 2.2 (32)
535i and M535i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 (33) 2.5 (36)
5-Series, E34 (“new-shape”)
518i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 (29) 2.0 (29)
520i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 (32) 2.1 (30)
525i, 530i and 535i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 (29) 2.3 (33)
Torque wrench settingsNm
Automatic transmission sump bolts
Three-speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 to 9
Four-speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 to 7
Spark plugs
M10 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 to 30
Except M10 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 to 33
Oxygen sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 to 33
Wheel bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Lubricants and fluids
Component or system Lubricant type/specification
Engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multigrade engine oil, viscositySAE 10W/40 to 20W/50, to API SG
Cooling system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ethylene glycol-based antifreeze with corrosion inhibitors
Manual transmission* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gear oil, viscosity SAE 80 to API-GL4, or single-grade mineral-based
engine oil, viscosity SAE 20, 30 or 40 to API-SG
Automatic transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dexron ll type ATF
Final drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . BMW-approved hypoid gear oil, viscosity SAE 90**
Brake and clutch hydraulic systems . . . . . . . . . . . . . . . . . . . . . . . . . . Hydraulic brake fluid to SAE J 1703 or DOT 4
Power steering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dexron ll type ATF
* E34 520i & 525i with air conditioning, E34 530i & 535i - Dexron II type ATF)
** Only available in bulk; refer to your BMW dealer
Capacities*
1•3
1
Engine oil
M10 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.0 litres
M20 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 litres
M30 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.8 litres
M40 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.0 litres
Cooling system
M10 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.0 litres
M20 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.5 litres
M30 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.0 litres
M40 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.0 litres
Fuel tank
3-Series, E30
Saloon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 litres (early),
64 litres (later)
Estate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 litres (early),
70 litres (later)
5-Series
E28 (“old-shape”) . . . . . . . . . . . . . . . . . . . . . . . . 70 litres
E34 (“new-shape”) . . . . . . . . . . . . . . . . . . . . . . . 81 litresManual transmission
ZF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 litres
Getrag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.0 to 1.5 litres
Automatic transmission (refill)
3-speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 litres
4-speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 litres
Final drive capacity (drain and refill)
3-Series, E30 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.9 litres
5-Series, E28 (“old-shape”) . . . . . . . . . . . . . . . . . . 0.9 litres
5-Series, E34 (“new-shape”) . . . . . . . . . . . . . . . . . 1.7 litres
*All capacities approximate
Servicing Specifications

1 Introduction
This Chapter is designed to help the home
mechanic maintain his or her vehicle with the
goals of maximum performance, economy,
safety and reliability in mind. Included is a
master maintenance schedule, followed by
procedures dealing specifically with each item
on the schedule. Visual checks, adjustments,
component renewal and other helpful items
are included. Refer to the accompanying
illustrations of the engine compartment and
the underside of the vehicle for the locations
of various components. Servicing the vehicle,
in accordance with the mileage/time
maintenance schedule and the step-by-step
procedures, will result in a planned
maintenance programme that should produce
a long and reliable service life. Keep in mind
that it is a comprehensive plan, so maintaining
some items but not others at specified
intervals, will not produce the same results.
2 Routine maintenance
As you service the vehicle, you will discover
that many of the procedures can - and should
- be grouped together, because of the nature
of the particular procedure you’re performing,
or because of the close proximity of two
otherwise-unrelated components to one
another. For example, if the vehicle is raised
for chassis lubrication, you should inspect the
exhaust, suspension, steering and fuelsystems while you’re under the vehicle. When
the wheels are removed for other work, it
makes good sense to check the brakes, since
the wheels are already removed. Finally, let’s
suppose you have to borrow a torque wrench.
Even if you only need it to tighten the spark
plugs, you might as well check the torque of
as many critical nuts and bolts as time allows.
The first step in this maintenance
programme is to prepare yourself before the
actual work begins. Read through all the
procedures you’re planning to do, then gather
up all the parts and tools needed. If it looks
like you might run into problems during a
particular job, seek advice from a mechanic or
an experienced do-it-yourselfer.
3 Engine “tune-up”-
general information
The term “tune-up” is used in this manual to
represent a combination of individual
operations rather than one specific procedure.
If, from the time the vehicle is new, the
routine maintenance schedule is followed
closely, and frequent checks are made of fluid
levels and high-wear items, as suggested
throughout this manual, the engine will be
kept in relatively good running condition, and
the need for additional work will be minimised.
More likely than not, however, there will be
times when the engine is running poorly due
to a lack of regular maintenance. This is even
more likely if a used vehicle, which has not
received regular and frequent maintenance
checks, is purchased. In such cases, an
engine tune-up will be needed outside of the
regular maintenance intervals. The first step in any tune-up or diagnostic
procedure to help correct a poor-running
engine is a cylinder compression check. A
compression check (see Chapter 2B) will help
determine the condition of internal engine
components, and should be used as a guide
for tune-up and repair procedures. If, for
instance, a compression check indicates
serious internal engine wear, a conventional
tune-up will not improve the performance of
the engine, and would be a waste of time and
money. Because of its importance, the
compression check should be done by
someone with the right equipment, and the
knowledge to use it properly.
The following procedures are those most
often needed to bring a generally poor-
running engine back into a proper state of
tune.
Minor tune-up
Check all engine-related fluids (Section 4)
Check all underbonnet hoses (Section 10)
Check and adjust the drivebelts (Sec-
tion 11)
Clean, inspect and test the battery (Sec-
tion 13)
Renew the spark plugs (Section 14)
Inspect the spark plug HT leads, distributor
cap and rotor (Section 15)
Check the air filter (Section 20)
Check the cooling system (Section 22)
Major tune-up
All items listed under minor tune-up, plus . . .
Check the ignition system (see Chapter 5)
Check the charging system (see Chapter 5)
Check the fuel system (see Chapter 4)
Renew the spark plug HT leads, distributor
cap and rotor (Section 15)
1•7
1
Routine Maintenance
Weekly checks
4 Fluid level checks
1
Note:The following are fluid level checks to
be done on a 250-mile or weekly basis.
Additional fluid level checks can be found in
specific maintenance procedures which
follow. Regardless of intervals, be alert to fluid
leaks under the vehicle, which would indicate
a fault to be corrected immediately.
1Fluids are an essential part of the
lubrication, cooling, brake and windscreen
washer systems. Because the fluids gradually
become depleted and/or contaminated during
normal operation of the vehicle, they must be
periodically replenished. See “Lubricants and
fluids”at the beginning of this Chapter before
adding fluid to any of the following
components. Note:The vehicle must be on
level ground when any fluid levels are
checked.
Engine oil
2Engine oil is checked with a dipstick, which
is located on the side of the engine (refer to
the underbonnet illustrations in this Chapter
for dipstick location). The dipstick extends
through a metal tube down into the sump.
3The engine oil should be checked before
the vehicle has been driven, or at least
15 minutes after the engine has been shut off.
4Pull the dipstick out of the tube, and wipe
all of the oil away from the end with a clean
rag or paper towel. Insert the clean dipstick all
the way back into the tube, and pull it out
again. Note the oil at the end of the dipstick.
At its highest point, the oil should be betweenthe two notches or marks (see illustration).
5It takes one litre of oil to raise the level from
the lower mark to the upper mark on the
dipstick. Do not allow the level to drop below
the lower mark, or oil starvation may cause
4.4 The oil level should be kept between
the two marks, preferably at or near the
upper one - if it isn’t, add enough oil to
bring the level to the upper mark
If the oil is checked
immediately after driving the
vehicle, some of the oil will
remain in the upper part of
the engine, resulting in an inaccurate
reading on the dipstick.

Every 6000 miles or 6 months, whichever comes first
1•11
6.17a Unscrew the bolt . . .
1
Every 6000 miles
6 Engine oil and filter change
1
Warning: Prolonged skin contact
with used engine oil is
hazardous. Use a barrier cream
and wear gloves during this procedure.
Change out of oil-soaked clothing
immediately.
1Make sure that you have all the necessary
tools before you begin this procedure (see
illustration). You should also have plenty of rags
or newspapers handy for mopping up oil spills2Start the engine and allow it to reach
normal operating temperature - oil and sludge
will flow more easily when warm. If new oil, a
filter or tools are needed, use the vehicle to go
and get them, thus warming up the engine oil
at the same time.
3Park on a level surface, and switch off the
engine when it’s warmed up. Remove the oil
filler cap from the valve cover.
4Access to the oil drain plug and filter will be
improved if the vehicle can be lifted on a hoist,
driven onto ramps, or supported by axle
stands.
Warning: DO NOT work under a
vehicle supported only by a
hydraulic or scissors-type jack -
always use axle stands!
5If you haven’t changed the oil on this
vehicle before, get under it, and locate the
drain plug and the oil filter. Note that on some
engines, the oil filter is located on the top left-
hand side of the engine. The exhaust
components will be hot as you work, so note
how they are routed to avoid touching them.
6Being careful not to touch the hot exhaust
components, position a drain pan under the
plug in the bottom of the engine.
7Clean the area around the plug, then
remove the plug (see illustration). It’s a good
idea to wear a rubber glove while unscrewing
the plug the final few turns, to avoid being
scalded by hot oil. Hold the drain plug againstthe threads as you unscrew it, then pull it
away from the drain hole suddenly. This will
place your arm out of the way of the hot oil, as
well as reducing the chances of dropping the
drain plug into the drain pan.
8It may be necessary to move the drain pan
slightly as oil flow slows to a trickle. Inspect
the old oil for the presence of metal particles,
which could give early warning of engine
wear.
9After all the oil has drained, wipe off the
drain plug with a clean rag. Any small metal
particles clinging to the plug would
immediately contaminate the new oil.
10Refit the plug and tighten it securely. Use
a new washer if necessary.
11Move the drain pan into position under the
oil filter.
Canister-type oil filter
12Loosen the spin-off type oil filter by
turning it anti-clockwise with a filter spanner.
Any standard filter spanner will work.
13Sometimes the spin-off type oil filter is
screwed on so tightly that it can’t be easily
loosened. If it is, punch a metal bar or long
screwdriver directly through it, and use it as a
T-bar to turn the filter. Be prepared for oil to
spurt out of the canister as it’s punctured.
14Once the filter is loose, use your hands to
unscrew it from the block. Just as the filter is
detached from the block, immediately tilt the
open end up to prevent oil inside the filter
from spilling out.
15Using a clean rag, wipe off the mounting
surface on the block. Also, make sure that
none of the old sealing ring remains stuck to
the mounting surface. It can be removed with
a scraper if necessary.
16Compare the old filter with the new one,
to make sure they are the same type. Smear
some engine oil on the rubber sealing ring of
the new filter, and screw it into place (see
illustration). Overtightening the filter will
damage the sealing ring, so don’t use a filter
spanner. Most filter manufacturers
recommend tightening the filter by hand only.
Normally, they should be tightened three-
quarters of a turn after the sealing ring
contacts the block, but be sure to follow the
directions on the filter or container.
6.1 These tools are required when
changing the engine oil and filter
1 Drain pan- It should be fairly shallow in
depth, but wide enough to prevent spills
2 Rubber gloves- When removing the drain
plug and filter, you will get oil on your
hands (the gloves will prevent burns)
3 Socket bar - Sometimes the oil drain plug
is tight, and a long bar is needed to loosen
it. The correct-size ring spanner may work
just as well
4 Socket- To be used with the bar or a
ratchet (must be the correct size to fit the
drain plug - six-point preferred)
5 Filter spanner - This is a metal band-type
spanner, which requires clearance around
the filter to be effective. This tool is not
required on all engines.
6 Filter spanner- This type fits on the bottom
of the filter and can be turned with a ratchet
or breaker bar (different-size spanners are
available for different types of filters) This
tool is not required on all engines.
6.7 Using a ring spanner to remove the oil
drain plug
6.16 Lubricate the oil filter sealing ring
with clean engine oil before refitting the
filter on the engine
Frequent oil changes are the
most important preventive
maintenance procedures that
can be done by the home
mechanic. As engine oil ages, it
becomes diluted and contaminated,
which leads to premature engine wear.

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,

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

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