Category Archives: Mini

Ceramic diesel glow plugs – their function and how to install

Glow plug technology can be divided into two major categories – metal sheathed types and  ceramic types. Ceramic glow plugs utilise a heating element which is encased in a special type of ceramic – Silicon Nitride. Ceramic glow plugs have the ability to heat up more quickly than metal types and in addition can gain higher operating temperatures for an extended period of time. They are also more compact making these features especially advantageous in modern engines.


Insulator – The insulator separates the electrically positive (Connection terminal) from the electrically negative part (Metal shell) of the glow plug.

Thread – The thread of a high-quality glow plug is always rolled and never cut. By this production method fast, accurate threads are formed, eliminating the possibility of damage to the glow plug bore in the cylinder head.

Centre electrode – The supply voltage is applied to the coils via the solid centre electrode.

Heating coil – Contrary to a metal glow plug, a ceramic glow plug uses a ceramic heating element.

Ceramic casing – The heating coil or heating element of a ceramic glow plug is encased in a high performance ceramic material: silicon nitride. It protects the coil from the high temperatures and vibrations created by the combustion process. It is also an excellent heat conductor, allowing the heat energy of the coil to be rapidly released into the combustion chamber.

Connection terminal – The supply voltage is applied at the connection terminal. This may be a threaded post to suit a connector which is secured by a nut or an unthreaded post to suit a push-on connector.

Metal shell – The metal shell of a glow plug usually provides the electrically negative pole (ground connection).

Taper seat – The taper seat provides simple but effective gas-tight sealing of the combustion chamber without the need for sealing gaskets, etc. Its compact form also allows bore sizes to be kept to a minimum. The taper faces also provide an excellent electrical ground (earth).

Contacting ring – The contacting ring provides the electrical connection at the junction of the centre electrode and the heating element.


Particular care must be exercised when installing ceramic glow plugs. When fitted, the ceramic is designed to withstand the arduous events that occur within in the combustion chamber, however they are more susceptible than metal types to damage caused by unsupported side loads or impact. Improper installation can make it unusable or even lead to damage to the engine.

1. Where possible the removal of a glow plug should take place with the engine at operating temperature to assist in releasing the plug.
2. Carefully loosen the glow plug.
3. Remove any loose debris around the glow plug with compressed air.
4. Unscrew the old glow plug.
5. Remove any carbon deposits from the glow plug bore – with a reamer if necessary – then clean and inspect the thread in the cylinder head.
6. Screw the glow plug in by hand until it seats in the cylinder head.
7. Set the torque wrench to the correct tightening torque.
8. Ensure that the socket of the torque wrench is correctly in line with the tightening nut of the glow plug and secure it.
9. Refit the electrical supply connection.

Zirconia switching Lambda sensor – function and operation

There are basically three different, non-interchangeable types of Lambda sensor. The zirconium dioxide and titanium dioxide Lambda sensors are also called switching, voltage jump or ‘binary’ sensors, because their output signal varies back and forth between two values, depending on whether the fuelling is in a rich or lean state. The third type is the broadband Lambda sensor.

Method of operation of the zirconium dioxide sensor
This sensor element has a hollow, thimble shaped design. The inside surface is in contact with ambient air. The outside surface is situated such that it lies in the stream of the exhaust gas. Both surfaces are covered with a thin, porous platinum layer which acts as electrodes.

There will always be a difference in the concentration of oxygen between the exhaust gas and ambient air. When the Lambda sensor reaches operating temperature, oxygen ions start to move through the ceramic electrolyte from the side that has a greater concentration of oxygen towards the side that has a lower oxygen concentration, attempting to reach a state of equilibrium.

As these ions leave one platinum layer and reach the other layer, a potential differential results, giving rise to an electrical voltage. If the mixture is lean, the voltage will be relatively low (approx. 0.1 volts). If the mixture is rich, it will be relatively high (approx 0.9 volts). There is a large characteristic voltage jump as the stoichiometric point (Lambda = 1.0) is passed.

Testing zirconia switching Lambda sensors
Testing with an oscilloscope is the most effective method. It shows minimum and maximum voltage, the response time and the frequency. When performing the test, the manufacturer’s specifications must be observed.

Test procedure
1. Bring the engine to operating temperature at 2,000 rev/min.
2. Connect the oscilloscope to a signal line without disconnecting the sensor from the engine control unit.
3. Set the measurement range to 1-5 volts and time to 5-10 seconds (observe manufacturer’s specifications).
4. If applicable, activate automatic signal recognition. A correctly functioning sensor swings between 0.1 and 0.9 volts with a frequency of 0.5-4 Hz.

Diagnosis tips
A visual inspection often provides the initial clues for a possible malfunction. Inspection points for the workshop are:

Resistance value of the heating element
If it is above 30 ohms then the sensor is defective.

Are they broken or is the plug broken? Is the cable seal intact? Has moisture penetrated into the plug? Are the plug contacts in good condition? Is the cable routing too tight?

Sensor body
Does the sensor show any visible damage?

Make sure you use the right sensor type
Each vehicle will have a specifically designed sensor type and therefore it is essential that they are only replaced with matching specification sensors. You can use the current NGK/NTK catalogues to identify the correct replacement sensor for each application.

A quick guide to ignition coils

The operating principle of the ignition coil is essentially the same for all types – whether the classic can-type coil, or in a coil rail system. The device contains two copper wire windings and a laminated iron core, with the copper wires featuring insulating materials to prevent short circuits.

The battery current fed through the primary winding produces a magnetic field whose strength is further increased by the iron core.

When this circuit is opened, the magnetic field collapses, inducing a high voltage pulse in the secondary coil. This pulse is fed through the H.T. connection to the spark plugs. As an integral part of the ignition system, the coil produces the high voltage required to produce the electric spark to ignite the fuel. The relatively low battery voltage, nominally around 12V, is then transformed to up to 45,000V.

How can 12V produce a high-voltage pulse?

The secondary coil consists of a very fine wire with many more windings than the primary coil. The winding ratio is typically between 1:150 and 1:200. This has the effect of multiplying the voltage whilst reducing the current. The voltage output from the device depends upon:

  • The value of primary circuit current
  • The ‘turns ratio’ of the windings
  • The change time of the coil
  • The rate of magnetic field collapse

The different types of ignition coil

The last few decades have seen great improvements in ignition technology. As a consequence, various new ignition coil types have been developed. Depending on the age of the vehicle, the engine design and the ignition system, any of these ignition coil designs might be used:

Can-type ignition coils
In older vehicles and vintage cars, you might still find what is commonly known as a can-type ignition coil. Some older versions of this type are filled with oil, which acts as an insulator and a coolant, but most have a more modern dry insulation design.

Distributor coils
For this type, the induced high voltage reaches the individual spark plugs via a mechanically driven distributor mechanism.

Ignition blocks
Ignition blocks contain several ignition coils, which are connected by H.T. cables to each plug. This ignition coil type is available with single or dual spark technology. In single-spark ignition blocks, each ignition cable supplies the high voltage pulse to one cylinder. In dual-spark blocks, the high voltage pulse is fed simultaneously to two cylinders: one that is on the power stroke, and the other being on the exhaust stroke and, thus, has a “wasted spark”.

Pencil or coil on plug ignition coils
This ignition coil type is mounted directly on top of the spark plug. The high voltage pulse is fed straight to the spark plug, minimising power loss. As pencil ignition coils are mounted in the spark plug tunnel, they do not take up space in the engine compartment. Pencil ignition coils are used in vehicles with electronic ignition systems and are available as single-spark or dual-spark coils.

Ignition coil pack systems
So called ‘coil packs’ combine a number of pencil ignition coils mounted within a single component, known as a ‘rail’. This rail is then placed across a bank of several spark plugs.

Lambda sensors explored

Tim Howes, Deputy General Manager – Supply Chain & Technical Service, NGK Spark Plugs (UK), looks at the origins of vehicle Lambda sensors and the various types.

The term Lambda is used to designate the value of the ratio of the mass of air supplied to an engine divided by the theoretical ideal requirement. That sounds very grand but, essentially, it means that if the engine is supplied with a fuel rich mixture it would have a Lambda reading of less than 1.0 Lambda. Alternatively, if it was supplied with a fuel lean mixture it would produce a reading greater than 1.0 Lambda. In most cases the basic function of a Lambda sensor is to ensure that the fuelling system supplies the engine with a mixture as close to 1.0 Lambda as possible.

Why the need for a 1.0 Lambda mixture?

Most engines needs to be supplied with this 1.0 Lambda mixture because it is the ratio of fuel and air that produces the most complete combustion, thereby providing an efficient use of fuel. The resultant exhaust gases can be dealt with effectively by a three way catalytic converter. This theoretically ideal ratio is called a stoichiometric mixture and for a standard petrol engine the air/fuel ratio is 14.7:1 by mass.

Sensors achieve this control by measuring the residual oxygen content of the exhaust gas before it enters the catalyst; this is why Lambda sensors are also (and more correctly) known as exhaust gas oxygen sensors (EGO). An oxygen concentration outside certain limits will result in the sensor signalling the ECU to amend the fuelling system calibration, thus bringing the mixture back into acceptable limits.

Sensor variations

There are several different types of oxygen sensor in use but, for the majority of cars, there are two non-interchangeable sensor types, using a different strategy to detect the oxygen concentration in the exhaust gas.

Zirconia type

This is by far the most popular sensor type. Under the protective metal end cap there is a thimble shaped ceramic element made from sintered zirconium dioxide. This has two thin micro porous platinum layers added: one covering the inside and one covering the outside. These layers are the electrodes to which the signal wires are attached. On top of the outer layer a further porous ceramic layer is added (aluminium and magnesium oxide) which protects the platinum from dissociation and erosion by the hot exhaust gases. The whole package is then fitted into a metal shell, part of which is threaded to allow fitment to the exhaust system.

This element is inserted into a convenient part of the exhaust system up-stream of the catalyst. The heat energy imparted by the exhaust gases will raise the temperature of the sensor. When 300°C is reached the Zirconia ceramic has a special property in that it becomes ‘permeable’ and will allow oxygen ions to pass through it. The centre of the thimble shaped ceramic element is hollow. This is to allow a pocket of ambient air to act as a reference gas.

In theory a stoichiometric combustion gas will have no oxygen present, however, in practice, small levels of oxygen are present. In an attempt to maintain equilibrium, oxygen ions will migrate through the permeable ceramic and platinum layers. The movement of these ions causes a voltage to be generated. Put simply, the sensor behaves like a small battery with the Zirconia acting as the electrolyte. In this way the voltage output is relative to the oxygen concentration in the exhaust gas.

Lean air fuel mixtures result in relatively small amounts of ionic movement due to the oxygen rich environment of the exhaust gas, whereas rich mixtures are deficient in oxygen, resulting in larger ionic movement as the sensor tries to achieve equilibrium across the element.

Around the stoichiometric point (1.0 Lambda) there is an abrupt and dramatic change in oxygen concentration, producing a large differential between exhaust gas and the reference air. This in turn produces a relatively large change in voltage. This voltage is the signal which is sent to the fuelling control system, enabling an adjustment to bring the air/fuel ratio back into the acceptable window around 1.0 Lambda. There is a natural tendency for the fuel system to overshoot the desired window, therefore the voltage output cycles – fuel lean/fuel rich between a minimum and maximum value – nominally between 0.1 V ~ 0.9 V. This occurs with a frequency of 1~2 Hz. If a gas analysis is carried out the reading may fluctuate between 0.9 Lambda and 1.1 Lambda.

Because the sensor has to reach 300°C before it starts to function there is a period after start up which is not controlled by the Lambda sensor. To combat this it is desirable to install the sensor as near to the engine as is practical. Under certain conditions exhaust gas temperatures can drop sufficiently to impair the function of an unheated sensor. A solution to both problems is to use a heater inside the sensor which rapidly brings the ceramic up to temperature. Heated sensors (HEGO) are therefore particularly desirable when trying to reduce noxious gas emissions. Most contemporary engine control systems are designed to work with heated sensors.

Titania type

The less common Titania sensors have a similar appearance but work in a different way. They use a layered titanium dioxide ceramic element with its electrodes sandwiched in between. At a critical point around 1.0 Lambda the Titania ceramic possesses the property whereby its electrical resistance changes substantially. If a small voltage is applied (typically 5 V) by the vehicle’s control system this change in resistance can be used to adjust the fuelling, keeping the exhaust gases within the desired limits. These sensors do not need access to ambient reference air.

Titania sensors are more expensive to produce but reach operating temperature faster, reaction times are faster and they can be made physically smaller. The sensor’s ceramic element requires a high degree of protection. This is provided by the metal end cap which has specially designed holes to allow a good flow of exhaust gas whilst preventing impact damage, water splash and extremes of temperature. Total protection against leaded fuel and some other air borne compounds can’t be provided, however. These unfriendly compounds can poison the sensor, slowing or preventing its operation.

Special types

There are some systems that allow the engine to run on considerably leaner mixtures under certain conditions and these require a special type of oxygen sensor called a ‘wide band’ or ‘broad band’ sensor. These are much more complex in operation with very sophisticated control mechanisms.

In addition, most road vehicles also have a second sensor fitted after the catalyst. This functions in the same way but is used to monitor the effectiveness of the catalyst and is often referred to as the CMS (catalyst monitoring sensor) or diagnostic sensor; this usually plays little part in regulating the fuelling system but can, on some applications, detect catalyst ageing and allow calibration changes to accommodate.

Spark plugs – the ‘small giant’ of the powertrain

Expert: Tim Howes, Deputy General Manager – Supply Chain & Technical Service, NGK Spark Plugs (UK) 

When it comes to automotive components the spark plug is the small giant of the powertrain. If someone else has coined that phrase before I apologise, but it is an extremely good description of the component that is the pacemaker at the heart of every petrol engine, the spark plug.

Precise control of ignition  has always been a critical part of the process in extracting the energy from the fuel but the more we demand in terms of power, torque, starting performance, economy and reduction in emissions the significantly greater this requirement becomes.

All components within the ignition circuit are under a great deal of stress and have to be significantly higher performance than in years gone by but they all operate in relatively moderate conditions when compared to the spark plug. After all these years it’s still the intense heat energy released by the spark as it jumps the electrode gap that initiates the combustion process.

So what is actually happening at the electrodes? Fundamentally, just before TDC on every firing stroke the ignition coil is instructed to apply a high voltage between an anode and a cathode – the plug’s electrodes.

Now as there is a significant gap, usually between 0.8-1.0mm between these two, initially current cannot flow – the circuit is ‘open’. However because the potential available voltage from the coil is so high (tens of thousands of volts) the structure of the gasses between the electrode surfaces begins to change.

Without writing pages on ultraviolet radiation generating photoelectrons which collide and by impact particle breaking eventually generate a higher electron number … no I’ll stop there and say that the air/fuel gaseous mixture becomes ionised allowing current to flow between the two. This is the spark!

Once the spark arrives the heat it produces starts the air/fuel mixture in the adjacent area to burn which then spreads in a completely controlled manner throughout the combustion chamber.  And this all happens over 8 times a second for each spark plug whilst the engine of an average family car is idling. It becomes mind boggling when one thinks of what is happening at the firing end of the plug in an F1 car where engine speeds are approaching 20,000 rev/min.

To obtain this performance we have to employ some specific materials when manufacturing spark plugs. We need to have both good conductors and particularly good insulators of electricity to contain well in excess of 30,000 V.

We also need materials that have high mechanical strength and a great ability to withstand extremes of temperature. These changes in temperature occur extremely rapidly due to the large amount of heat generated by combustion being immediately cooled by the incoming fresh charge of air and fuel. Under extreme conditions the force of shock from combustion vibrations can reach 50G or 50 times the force of gravity.

The base material of the insulator –the white part – is aluminium oxide which we obtain from bauxite, one of the most common compounds found on earth. This high purity aluminium oxide powder is doped with other material to further enhance its mechanical, thermal and dielectric properties. After forming it is sintered and glazed to produce the familiar hard smooth form of the plug. The resultant insulator is so good for its intended purpose that it has not changed significantly for many years. The main electrode is formed from copper and a nickel alloy, offering good electrical and heat conduction with high wear resistance.

To increase wear resistance further, especially when very fine electrodes are required small chips of semi-precious metals such as platinum or iridium alloys are welded to the nickel alloy. Iridium for example is extremely hard, has a particularly high melting point and is probably the most corrosion resistant metal available. This allows diameters of 0.4mm to be employed at the centre electrode. This offers several advantages of improved ignition performance and increases service life.

The electrical noise suppression resistor is located within the insulator ‘in series’ with the main electrode and is formed from a mixture of conductive carbon and insulating glass powder. Varying the proportions of the two materials allow different target resistance values (as required by the OEMs) to be achieved easily without fear of degradation during the service life of the plug. The normal target value is 5 kilo ohms.

The metal shell that houses the insulator will have one or more electrodes welded to it. Depending on application these may nickel alloy or inconel. Inconel is often employed where special resistance to high temperatures is required and as a further refinement a layered copper design can be used. So even the small J shaped ground electrode that you pay little or no attention to when handling a plug has a lot of thought put into its design. The sealing washer that gets compressed upon installation is usually of folded mild steel construction but can be stainless steel which guards against vibration or even solid copper to promote good heat transfer.

So what goes wrong when experiencing a perceived spark plug problem? Well I have heard that plugs cause problems as varied as misfires to flat tyres… and I am not joking. It must be remembered that if the plug is the correct one specified for the application, is within its recommended service life and it has been installed correctly it is highly unlikely that the plug is the root cause of any problem. The plug produces no heat or deposits; it’s the combustion process that does that and the poor old plug has to suffer all that is thrown at it.

When cars get older all the equipment on board starts to tire, for instance weak coils often wreak havoc and renewing the plugs can temporarily take some of the load off these components leading to a misdiagnosis of the true fault. Whether you simply sell or actually install these little marvels of technology spare them a little more thought.

Ignition Coils – Everything you need to know


Look under the bonnet of a modern vehicle and there is no doubt that the scene appears different to that of one of yester-year. With regards to ignition, distributors and lead sets are now a rarity – replaced with ‘plug top’ coils and ‘rail’ coils.

The ignition coil sector is now a significant part of the business of NGK Spark Plugs (UK). Although we recognise the importance of still catering for the earlier vehicles, many of which utilise the old metal can type ignition coils which incorporate oil to provide insulation and cooling, we also supply coils for the modern vehicle models that are venturing out of the main dealer network for repair.

What causes the demand for ignition coils is the harsh environment in which they work, which in turn creates a greater possibility of failure. As a result, although not strictly service items as such, many technicians view them in that category.

Coil manufacture has to be of a very high standard these days, mainly due to the high temperature fluctuations they’re subjected to. Many are mounted directly on the spark plugs and the severe cooling/heating cycles that prevail are a test for even the best quality item.

It is worth investing in suitable coil removal tools, not only to make removal easier upon servicing, but to ensure that the body or housing is not twisted or distorted – which can cause unseen damage internally.

Strict quality processes
Compromises on coil quality due to choice of materials used or production costs should never be made without recognising that there is inevitably a significantly greater possibility of premature failure.

The ignition coils in the NGK range have been through strict quality processes, from the initial design stage to assembly and testing. The testing carried out prior to launch ensures the items meet or exceed the vehicle manufacturers’ OE items.

The quality processes also encompass the packaging in which the items are shipped. Attention to detail means that items are safe in transit and, to ensure correct fit first time, the NGK ignition coil packaging includes a label with a schematic diagram of the coil contained inside – so selection can be verified easily without removal from the box.

Coil selection can be made using NGK Partfinder found on the website and the current NGK ignition coils application catalogue is available in paper format, which includes enhanced coil images to further aid selection.

The most recent additions to the NGK range, which was launched in 2013, were 22 new coil types covering vehicles including the VW Up, Mini, Vauxhall Adam, Vauxhall Astra J, Vauxhall Mokka, Mazda 6, Renault Clio IV and Dacia Sandero II. Range expansion is on-going, with emphasis revolving around demand. In total, the range now comprises 340 ignition coils, thus offering a part for a high percentage of the UK car parc.

You can talk to the NGK Spark Plugs (UK) technical team and find out more about its ignition coils range by visiting Stand C28 at Donington Park.

A guide to understanding and offering a safe hybrid service

Regulatory demands for better fuel economy and reduced emissions will continue to drive the increase in hybrid vehicles on the road in the future.

In fact, by 2020, it is projected that volumes will nearly triple from the two-million vehicles produced in 2012, so there is no doubt we will continue to see an increase in the number of hybrids entering the aftermarket once the warranty period ends.

Due to the high-voltage circuits contained in most hybrid vehicles, proper service takes on a whole new approach. Improper handling of the hybrid system may result in electrocution and damage to vehicle components, so it is important to closely follow the service procedures found in the approved VM repair manual when servicing these vehicles.

Each hybrid is unique and the proper processes need to be followed for locating/removing or switching off service plugs/switches prior to servicing the vehicle. There are a variety of tools required to help diagnose and service hybrid vehicles.

First, and foremost, a quality diagnostic scan tool is critical for accurate repairs. Additionally, a Category III DVOM is a must for diagnosing high voltage hybrid vehicle circuits. Meters such as the Fluke 1587 allow for insulation testing as well as performing all the other functions of a CAT III meter.


1. Always wear high-voltage insulated gloves rated to 1,000V (minimum) while diagnosing and servicing hybrid vehicles and systems. Use gloves that are in good condition, even as pinholes, can be very dangerous. One way to ‘method-test’ a rubber glove for leaks is to blow into the glove and hold it tight by squeezing or rolling the open end tight. If the glove has a leak it will deflate.

2. High-voltage circuits are typically identified by bright orange cables or wires. The wiring may also be covered by bright orange covers or conduit. When hybrid vehicles are in a workshop, the vehicle may need to be moved, so it’s important to remember that if you’re rolling a vehicle in the garage, with the drive wheels on the ground, the motor generator may be providing power to these circuits. To avoid this condition, wheel dollies are recommended to move hybrids around the workshop.

3. Always remove all jewellery, including watches, necklaces and earrings, when working on a hybrid vehicle. Metal objects conduct electricity and could be a hazard if it inadvertently contacts a voltage source. You should also wear the appropriate protective clothing (high-voltage rubber gloves, face shield, insulated boots, protective coat or apron) when servicing these vehicles.

4. During diagnosis, do not drive the vehicle when it is in “Service Mode”, as it may damage the transmission or other components of the hybrid system. To reset the vehicle, shut it off and restart.

5. If a hybrid is equipped with a “smart key” system, technicians need to be sure the system is disabled prior to performing any servicing work. When in “Ready Mode”, the engine can start at any time, which could create a safety concern if this occurs during vehicle service.

Helping to prevent drive train noises

In the UK Schaeffler is renowned for its leading LuK clutch, INA tensioner and FAG wheel bearing brands, and the company always goes the extra mile to provide even better products for its customers. This was demonstrated by the efforts it made when building a new acoustic testing facility at its Technical Development Centre in Herzogenaurach, Germany.

A room within a room
A special feature of the facility is a ‘room-in-room concept’, where an entire room is spring-mounted inside a larger room so that it moves independently and can be completely isolated as it is decoupled from the oscillation of the rest of the building. Special bricks were imported from Sweden as the interior rooms had to be of particularly high density (at least 2,400 kg/m³). Unsurprisingly, it has been named ‘the wobble room’ by staff!

The company’s engineers in the Competence Acoustics Centre (part of the Technical Development team) investigate the origins of irritating noise using the latest state-of-the-art analytical methods to discover how noise is generated and what can be done to eliminate it at the beginning of development. As such, typical tasks include investigations of airborne sound and vibration behaviour in the vehicle drive train, as well as in the chassis and its components, such as ball screw drives and roll stabilisers.

In addition, engineers also examine plain bearings and rolling bearings of all types and designs that are used in applications such as production machinery, wind turbines, hydroelectric power plants, railway, medical technology and household applications.

Vehicle test stand: here vehicles up to the size of a delivery van can be examined from a noise technical point of view.

Hi-tech equipment
Equipped with state-of-the-art measurement and computer technology, three test rooms and the so-called ‘wobble room’ have been installed in a 180 square metre area.

CTO Prof. Dr. Peter Gutzmer said: “This is an audible and tangible further extension of expertise at Schaeffler. With the new Herzogenaurach acoustic centre, we have created ideal conditions to further optimise the globally networked development activities at Schaeffler and adapt to customer needs even better than before.”

Especially in the field of drive technology, customers are paying more and more attention to low friction coupled with the quiet operation of the individual system components, and this is also true for bearings in electric motors and devices for the home and office environments.

Acoustic issues from all areas of automotive and industrial engineering can also be addressed quickly and competently.

Dr. Arbogast Grunau, Senior Vice President Corporate R&D Competence and Service, said: “The expertise concentrated here is the result of long-standing experience in product and system development and it is continuously being developed further.

“We use our network of competence to spread our knowledge and experience throughout the world, with training and seminars being an important medium. In this way we make an important contribution to Schaeffler’s global alignment, true to our motto ‘Together we move the world’ – here with a particular focus on noise optimisation.”

Examination of airborne sound and vibration behaviour of car wheel bearings in an anechoic room

Reducing outside noise
The test rooms include a large acoustic vehicle test bay, a room for fatigue tests and one with extensive adaptation options. The ‘room-in-room concept’ covers 30-50 square metres of floor space with the largest room weighing more than 130 tons.

The interior ceilings and walls of the test rooms are lined with up to 35cm thick acoustic broadband compact absorbers to meet the sensitive metrological requirements of the acoustic staff.

Dr. Alfred Pecher, Manager, Testing Competence Centre Acoustics, said: “This constructional measure means it has also been possible to reduce noise intruding into the test rooms from outside – such as the sounds of trucks passing by – to a minimum, and to obtain technically accurate measurements.”

 Even large-size bearings weighing several tons can get inside the acoustic centre by means of a crane system, designed specifically for this purpose. They can also be examined there.

How to change a clutch on a BMW 3 Series

The 3 series is the best selling model in BMW’s range, representing nearly 30% of sales for BMW. A clutch replacement on this model is really straight forward and, with the guidance of the LuK ‘Clutch Clinic’, the whole process will become even easier.

Launched in 1975 the BMW 3 series has seen many updates over the years, winning lots of awards along its journey. A compact executive car, its popularity is unlikely to diminish, meaning the likelihood of one arriving at your garage will remain pretty high.

We used a two-post ramp in this article, however a four-post ramp would also be suitable. A transmission jack, a long axle stand and a special alignment tool is also required.

Disconnect the battery earth lead and raise the vehicle. Unbolt and remove the plastic under-tray which will expose an alloy plate that should also be removed. Remove the front section which exposes the exhaust bracket that is bolted to the gearbox; this can be removed later as it is fixed with three bell housing bolts. Support the rear exhaust silencer and unbolt the two supporting brackets. Split the rear section of the exhaust from the front section and carefully lower out of the way to gain access to the heat shield. Unbolt and remove the heat shield to expose the propshaft.

Remove the crossmember support for the gearbox

Support the gearbox using the long axle stand and remove the cross member support for the gearbox.

How to change a clutch on a BMW 3 Series

You may need to carefully bend the heat shield out of the way to allow better access to the bolts. Unbolt and remove the slave cylinder and stow to one side. Unclip the reverse light switch on the side of the gearbox.

How to change a clutch on a BMW 3 Series

Remove the bolts holding the propshaft centre bearing then mark the propshaft position and remove the bolts holding the propshaft to the gearbox. Carefully swing the propshaft to the side and secure out of the way using bungee ties. This allows plenty of room to remove and lower the gearbox.

The exhaust bracket from earlier can now be removed, along with the three bell housing bolts. Disconnect the gear mechanism by removing two pins – they are held by two metal tabs that are prised upwards.

How to change a clutch on a BMW 3 Series

Remove the clip from the gear mechanism to the gear lever and tap it off, however be careful not to lose the two small nylon shims either side of the link arm.

How to change a clutch on a BMW 3 Series

Remove the 10mm bolt from the gearbox closing plate and remove the remaining bell housing bolts – the two top bolts are a little tricky. Knock the starter motor dowel through the bell housing using a punch to release the starter motor. Once the bell housing bolts are removed, carefully lower the gearbox to the floor. Remove the worn clutch, bearing and fork. It is important to remove the worn fork pivot and replace it.

How to change a clutch on a BMW 3 Series

In this example the dual mass flywheel (DMF) was also replaced with the clutch and bearing, however, in most cases you have no need to replace the DMF as this can be checked whilst on the vehicle for signs of heat stress and evidence of grease loss. The DMF should also be tested for free play and rock between the primary and secondary masses. LuK tool number 400008010 is specifically designed for this purpose and full instructions and DMF tolerances can be found by searching “DMF data sheet” at

Clean the first motion shaft splines and any debris from the bell housing (especially important when a release bearing has failed). Put a small dab of high melting point grease (not a copper-based product) on the first motion shaft splines and make sure the new driven plate slides freely back and forth. This not only spreads the grease evenly but also makes sure you have the correct kit. Wipe any excess grease off the shaft and driven plate hub.

Fitting the new clutch
Fitting of the new clutch will require a special tool. The clutch is a self-adjusting clutch type and it is also fitted with a transit locking plate between the wear cradle and diaphragm springs. Note: do not remove this locking plate until the clutch is bolted to the flywheel.

How to change a clutch on a BMW 3 Series

After checking the spigot bearing check the adjusting springs on the new clutch pressure plate to make sure they are fully compressed. Fit the clutch alignment tool and locate it into the spigot bearing on the flywheel. Place the driven plate over the alignment tool, making sure the correct side is facing the gearbox (note: ‘Getriebeseite’ means ‘gearbox side’ in German).

How to change a clutch on a BMW 3 Series

Bolt on the pressure plate, tightening each opposing bolt progressively around the cover until the desired torque setting is reached. Once the driven plate is secured the locking plate can now be removed. To remove this use an appropriate sized Allen key in the centre of the plate and rotate it anticlockwise – this can be discarded once it has been removed. Finally remove the alignment tool by using an appropriate size bolt. Refitting is the reverse of removal.

EPDM belts and ABDS systems – service and repair tips

When examining a multi-ribbed drive belt, it is important to be aware that changes to the materials used in its construction mean that some of the visible wear indicators that could be applied to belts of the past are no longer applicable.

For example, experienced drive belt installers will recall some of the more common wear characteristics of the Auxiliary Drive Belt System (ABDS) belts made using Neoprene. Designed with a life expectancy of around 50 to 60,000 miles, as the end of their operational life approached, wear became obvious. This included:

  • Cracks in the belt
  • Missing chunks of material
  • Rib separation

These visible signs helped technicians to confirm the need for belt replacement.

Belts made from EPDM

These days, multi-ribbed belts are commonly made from a quite different material known as EPDM. These belts are stronger and designed for much higher mileages, but the material does not crack with age. They are still subject to strain, stress and wear yet the visible evidence is not so obvious.

Concerned that technicians should be better equipped to identify the signs of wear to multi-ribbed belts and pulleys, when Gates introduced its new Micro-V Horizon belt (of which the entire range is made from EPDM see image below) at the end of 2012, the company also took the opportunity to announce the availability of a new Wear Indicator Tool that is easy to use and can help to identify the signs of wear in both belt and pulley.

Micro-V Horizon made from EPDM

Signs of wear

It’s essential to understand the wear process. As belts made from EPDM age, they gradually lose rubber material. It’s a similar story to the loss of tread in tyres and there are consequences for vehicle safety, too.

For example, a loss of belt material will change the belt profile, with the following potential implications:

a) Less tension to the belt

b) Belt slip

c) Reduced power to dependant systems such as power steering, cooling and electrical systems

Belts must be inspected for material loss in order to guarantee that they can deliver the power required consistently, without the risk of failure. As such a different diagnostic approach is required (pictured below).

Pattern of wear

The diagrams (below, left) show the pattern and progress of wear on a new belt made of EPDM. As it gets older, note that material is lost from several areas. There is loss of material at the sides of the ribs and at the belt seating points. This increases the area occupied by the pulley, which must fit perfectly in order to perform efficiently. The wider space adversely affects the overall performance and provides greater opportunities for slippage.

The degree of wear to the belt can be easily detected with the help of the Gates Belt Wear Indicator Tool, which can also be used to check for wear on the pulleys (pictured below).

Testing for wear

Testing belts and pulleys The Wear Indicator Tool has two separate profiles. The broader profile is for the belt, while the narrower profile is used for assessing wear to the pulleys.

With the belt still fitted to the ABDS, reach under a straight section of the belt and insert the broad ‘belt’ profile into the grooves between the belt ribs. The teeth of the indicator must fit perfectly within the profile of the grooves of the belt. No side-to-side movement must be possible without lifting the tool out of the belt grooves. If movement is detected, either excessive material has been worn away from the belt or the belt is operating at less than optimal power transmission.

Testing for wear to the pulleys is even more straightforward. Once again, testing can be carried out while the ABDS belt is fitted. The teeth of the tool must fit perfectly into the pulley, with only a thin parallel space evident between the pulley and the teeth of the tool.

If side-to-side movement is possible either excessive plastic or metal has been worn away or pulley-ribs may be rounded instead of straight. A new belt running on a pulley that has not been replaced will have less than optimal grip and its power transmission capabilities will be compromised.

ABDS considerations

Note that technological innovation within the ABDS means that some VMs have replaced ordinary crankshaft pulleys with Torsional Vibration Dampers (TVDs), which absorb vibration and improve the engine’s noise, vibration and harshness (NVH) characteristics. Overrunning Alternator Pulleys (OAPs), which allow more heavyduty alternators to ‘freewheel’ or ‘overrun’ whenever the engine decelerates, are increasingly found inside the modern ABDS. As a result, Gates recommends that all components are replaced simultaneously.