LV24 diesel fuel systems (2)

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Student Workbook

LV24 Diesel Fuel Systems (2)

kap all phase 2 & 3 6/11/03 11:36 am Page 17

Student Workbook for Technical Certificates in

Light Vehicle Maintenance and Repair

MODULE LV24 DIESEL FUEL SYSTEMS (2)

Contents

Safety Precautions: 3 Control Cable Adjustment: 22

Routine Maintenance: 3 Drive belt adjustment 25 Filter replacement 4 Adjustment mechanisms 26

Filter replacement notes – applicable Drive belt tension adjustment 28

Filter replacement – paper type Injector Maintenance/Cleaning: 30

Filter replacement – cartridge type 10 Chemical cleaners 31 Filter replacement – sandwich type 11 Ultrasonic cleaning 31 Water contamination 12 Stripping and cleaning 32

Additional fuel filters 14 Nozzle opening/break-off pressure 33

Fuel System Bleeding: 15 Spray patterns 34 Low pressure system – vacuum Nozzle leakage 34

Low pressure system – pressure type 16

Bleeding procedure – vacuum type

systems 19

Bleeding procedure – high pressure

system 20

Page Page

Servicing/Maintenance Checks: 38 Environmental Issues: 51 Pipelines 39 EU emissions standards for

Return pipe/hoses 40 Carbon monoxide (CO) 52

Carbon dioxide (CO2) 52

Glow Plug and Circuit Testing 42 Particulate matter (PM) 52

Fuel Injection Faults: 44 Principles of combustion 53

Black exhaust smoke 47

Diesel Fuel and Emissions: 49

Boiling point range 49

Cold flow properties and filtration 50

Safety Precautions

Foreword

Diesel fuel systems operate at both low and extremely high pressures Some components have fluid connections to both low and high-pressure sections and it is sometimes easy to confuse the two, especially in adverse working conditions A leak in the low pressure system can produce an intense spray

of fuel and it is therefore advisable to apply the same precautions to all parts

of the fuel supply system

Routine Maintenance

Routine maintenance of diesel engines is an important factor in the reliability and longevity of diesel engines With proper maintenance these engines will run for many thousands of miles, often under harsh driving and environmental conditions If they are not looked after however, small faults can lead to serious engine damage in a very short time Many diesel engines are fitted to small commercial vehicles (mainly light vans), which may be driven by a number of people who do not actually own the vehicle or have an interest in its running This can lead to longer than normal service intervals and missed maintenance

Routine maintenance is much more than simply following a list of “things to do” A skilled technician will spot potential problems early, allowing prompt action to prevent more complicated faults developing

Filter replacement

Fuel filters prevent potentially damaging particles getting into the sensitive components of the diesel injection system and as such are a vital part of the diesel fuel system, and they need to be replaced at regular intervals Just by doing the job they were designed to do, that of preventing anything other than clean fuel proceeding further along the fuel system towards the engine, they retain these particles and will eventually become clogged

Filters will naturally retain almost any foreign bodies entering the fuel system including particles of dirt, fluff from rags and paint flakes from the inside of tanks and cans In some cases, when the temperature is very cold, typically below –15°C, the filter may also retain crystal deposits formed from natural waxy elements within the fuel itself

Over time the flow of fuel through the filter will be reduced by the particles retained within the element, and when this flow reduction reaches a critical point the lack of fuel flowing to the injection system will eventually promote engine misfiring, stalling and even non-starting This is the point at which the filter is often described as being “blocked” In many fuel injection systems the fuel serves as a lubricant and damage can be caused to vital components if the fuel flow is sufficiently reduced by blocked filters Service intervals are designed to help ensure that the filter is replaced before the build-up of dirt etc within the filter becomes excessive

Water is often present in diesel fuel, normally caused by condensation in the vehicle fuel tank and in tanks where the fuel is stored prior to reaching the vehicle Most filter assemblies incorporate a drainage system to allow water

to be removed at regular intervals and to drain the assembly when replacing the filter Water collecting in the system is damaging to injection system components and may cause engine running/starting problems

Cartridge type – disposable, metal cased cartridge screwed directly to the filter head

Sandwich type – disposable, metal cased cartridge with exposed ends,

clamped between the filter head and sediment bowl by a long bolt

Rubber sealing rings are normally fitted between the filter or filter bowl and the filter head Filter elements may have rubber seals attached to them and sealing rings are also normally installed where bolts pass through the filter It

is normally recommended that these seals are replaced at the same time as the filter and in some cases they may be included as part of a replacement filter kit

Filter replacement notes – applicable to all types

Before any dismantling is attempted remove the fuel filler cap – during normal running a small amount of pressure may build up in the tank and fuel lines This pressure may force fuel out of the system when components are

removed with an associated risk of injury Removing the filler cap first will ensure that this pressure is released before any dismantling takes place

Disconnect any electrical cables which may be attached to switches/sensors

on any part of the filter assembly which is turned or unscrewed when the filter

is removed – some filters require many turns to unscrew them fully and wiring

or components may be damaged if they are twisted during filter removal Additionally, disconnect any wiring attached to components in the area if there

is a risk that they may be damaged in the filter changing process

Place a suitable container beneath the filter bowl to catch any fluid drained In some cases it may not be possible to catch the fluid directly beneath the filter due to lack of space In these cases it will difficult to prevent fluid splashing onto other mechanical and electrical components and/or paintwork Where spillage is unavoidable the use of rags in the area may be necessary to

reduce splashing and a drip tray should be used to prevent fluid reaching the floor Clean any spillage from vehicle components and the working area Take careful note of the position and orientation of any clips, springs and washers during dismantling so that the assembly can be re-built correctly – it

is possible that incorrect assembly can cause blockages, air leaks or even a total lack of filtering

Before disposing of the old filter element and seals, use them as patterns to check that the replacements are of the same size and type Dispose of the old filters according to local regulations and procedures

Filter replacement – paper element type

See the filter replacement notes above

Some filter bowls incorporate a drain plug or tap and in certain cases a drain hose may also be fitted Where possible, drain the fluid from the filter into a suitable container by partly unscrewing the plug/tap Tighten the plug/tap when all the fluid is drained in order to prevent spillage of any remaining fluid when the filter is finally removed Tightening the plug/tap at this stage has the added advantage of reducing the chance of forgetting to tighten it later

Remove any drain hoses at this stage if there is a chance they may be twisted during filter removal

Where the filter bowl is screwed directly to the filter head, unscrew the entire bowl and remove it to a drip tray If the bowl is too tight to remove by hand, use a strap wrench Alternatively, the filter bowl may be held in place by a bolt, fitted either downwards through the filter head into the filter bowl or

upward from the bottom of the filter bowl into the head Remove this bolt, noting the position of the filter and that of any seals or washers and place the filter bowl in a drip tray

In some cases, the filter element is held in place by the filter bowl itself and removing the bowl will normally allow the element to be removed at the same time Sometimes however, the filter element will remain attached to the filter head by a bolt, threaded sleeve or nut after the bowl is removed Where applicable remove the fixing and filter element, noting its position and avoiding any fuel spillage Note the position of any seals or washers during removal

Clean the filter bowl, seal recesses and fixings with a lint-free rag and replace any damaged seals or gaskets Some seals are normally replaced as a

matter of course even if they appear undamaged, particularly the seal

between the edge of the bowl and filter head

Before disposing of the old filter element and seals, use them as a pattern to ensure that replacements are of the same size and type

Fitting the new filter is the reverse of removal Apply a smear of clean diesel fuel to the seal between the filter bowl and the filter head to help the bowl seat itself properly

To save time and effort when priming the system later, partly fill the filter bowl with clean diesel fuel at this stage, allowing for displacement of fuel by the filter itself This may not be possible, especially when the bolt securing the filter bowl passes all the way through the bowl

Carefully fit the filter and bowl, ensuring they seal together properly without over-tightening Make sure the filter is fitted the correct way up – some filters will be marked Use the manufacturers’ recommended torque settings when

Re-connect any switches/sensors that have been removed and connect any drain hoses, ensuring they are secured correctly both to the filter bowl and to any fixings along their length

Bleed the fuel system to remove any air

Filter replacement – cartridge type

See the filter replacement notes at the beginning of this section

Many cartridge type filters are sealed, one-piece units with no drain tap It is sometimes difficult to remove these without fuel spillage as they are normally full of fuel and care should be taken to prevent too much splashing

Some cartridges are fitted with a removable drain plug or tap and a drain hose may be fitted In these cases, drain the fluid from the filter into a suitable container by partly unscrewing the plug/tap Tighten the plug/tap when all the fluid is drained in order to prevent spillage of any remaining fluid when the filter is finally removed Remove any drain hoses at this stage if there is a chance they may become twisted during filter removal

Unscrew the filter cartridge, by hand or by using a strap wrench where

necessary, ensuring the old seal is removed at the same time

Clean the filter head including the seal recess with a lint-free rag

Remove any drain plugs/switches etc attached to the old filter cartridge that are needed on the new one and secure them to the replacement cartridge

Ensure the seal is correctly attached and properly located on the new filter cartridge and apply a smear of clean diesel fuel to the seal As before, it may

be possible to partly fill the cartridge with clean diesel fuel at this stage

Screw the filter to the head using hand effort only

Re-connect any switches/sensors and connect any drain hoses, ensuring they are secured correctly both to the filter bowl and to any fixings along their length

Bleed the fuel system to remove any air

Filter replacement – sandwich type

See the filter replacement notes above

Some filter sediment bowls incorporate a drain plug or tap and in certain cases, a drain hose may be fitted Where possible, drain the fluid from the filter into a suitable container by partly unscrewing the plug/tap Tighten the plug/tap when all the fluid is drained in order to prevent spillage of any

remaining fluid when the filter is finally removed Remove any drain hoses at this stage if there is a chance they may be twisted during filter removal

Remove the bolt clamping the assembly together; noting the position of any seals or washers and place the filter and sediment bowl in a drip tray

Clean the filter head, sediment bowl, seal recesses and fixings with a lint-free rag and replace any damaged seals or gaskets Some seals are normally replaced as a matter of course even if they appear undamaged, particularly those seals between the sediment bowl and filter, and between the filter and

Fitting the new filter is the reverse of removal Apply a smear of clean diesel fuel to the seals and ensure the filter is fitted the correct way up; it may be marked Tighten the fixing bolt to the correct torque as described by the manufacturer

Re-connect any switches/sensors that have been removed and connect any drain hoses, ensuring they are secured correctly both to the filter bowl and to any fixings along their length

Bleed the fuel system to remove any air

As fuel passes through the filter element, any small particles of water carried with it tend to combine into larger, heavier droplets in a process called

agglomeration This is why the filter assembly is sometimes known as an agglomerator As water is heavier than the fuel, the fuel droplets sink to the bottom of the filter bowl and remain there until removed during servicing

At pre-determined service intervals or when excessive quantities of water have entered the system, it will be necessary to remove the water even

though filter replacement may not be specified or necessary at that time or mileage Water can usually be drained through a tap or drain plug at the base

of the filter bowl The low pressure caused by water leaving the bowl should ensure that fresh fuel is drawn into the filter

Draining water

Place a clean container beneath the filter bowl to catch any fluid drained In some cases, it may not be possible to catch the fluid directly beneath the filter due to lack of space In these cases, it will difficult to prevent fluid splashing onto other mechanical and electrical components and/or paintwork Where spillage is unavoidable, the use of rags in the area may be necessary to reduce splashing and a drip tray should be used to prevent fluid reaching the floor

Partly unscrew the cap or plug, allowing the fluid to drain into the container Water will be seen as clear, bubble-like droplets within the coloured diesel fuel Continue to drain the liquid until no more droplets of water can be seen, then turn off the tap If a lot of water has been removed, it may be difficult to determine if water is still leaving the filter Empty and clean the container then repeat the process to check Try to drain off only as much liquid as is

necessary to remove the water in order to minimise the need to bleed the system later

Start the engine and check that it runs smoothly at all speeds It may be necessary to bleed the fuel system if the engine does not run properly

Run the engine for a few minutes to ensure the system is completely filled with fuel Sometimes, after draining water, the engine will start and run for a short time even though excessive air has entered the system This may give the impression that all is well until later when the engine may not start

Additional fuel filters

Many diesel fuel injection systems are fitted with additional filters, normally located in the connection where the fuel feed pipe reaches the high pressure fuel injection pump These filters are the final opportunity to prevent

potentially damaging particles of dirt etc reaching sensitive components

Theoretically, the main filter should prevent all foreign objects reaching these additional filters but it is possible that dirt can enter the fuel lines after the main filter, particularly during routine maintenance or when the system is dismantled for repairs

Most of these filters are of the wire or plastic gauze “basket” type and usually form part of the fuel pipe connector bolt assembly or become accessible within the pump when the bolt is removed As with all filters, they will

eventually become blocked if not maintained correctly

At specified intervals, the filters should be removed and cleaned The

connection bolt and pipe should also be cleaned before re-assembly, taking special care to ensure that dirt or cloth fibres do not enter the pump or pipe-work Cleanliness is essential here as these filters are normally the last

chance to protect the pump and injectors

Fuel System Bleeding

Bleeding becomes necessary when air enters the fuel system This can happen when the vehicle runs out of fuel, during servicing/repair of

components anywhere in the system or when leaks occur In the majority of cases, air in the system will give rise to rough running and very often, the engine will not start at all This is because the lift pump providing fuel to the high-pressure fuel injection system is not normally designed to pump air Air may be present in both the low-pressure and high-pressure parts of the fuel system and different procedures are required to remove it from these areas

Low pressure system - vacuum type

Many fuel supply lift pumps are fitted on the engine or fuel injection pump assembly and fuel is drawn through the system from the tank, as pump action reduces the pressure in the pipe work/fuel lines, including the filter Fuel reaching the pump is delivered under low pressure to the high-pressure fuel injection pump Leaks between the tank and pump will allow air to be drawn into the system, which will subsequently pass through the pipe work with the fuel until it reaches the pump Air reaching this point usually means the flow

of fuel will cease

In a few cases, where very small quantities of air are involved, the air will remain mixed with the fuel and may eventually bleed itself out when the

engine is cranked or as it runs Small leaks in this type of system are difficult

to detect because the pressure in most of the fuel lines is lower than

atmospheric pressure when the engine is running and leakage of fuel may not

be obvious

These systems often incorporate a hand operated priming pump This pump may be fitted anywhere between the tank and the engine but it is commonly incorporated into the filter assembly, low-pressure pump or the high-pressure pump assembly A large button, a lever or a plunger assembly, may be used

to operate the priming pump

Low pressure system - pressure type

Some systems use an electric feed pump mounted within, or close to the tank, which supplies fuel to the high-pressure injection pump The electric pump is capable of supplying enough fuel to cope with maximum engine speed and load and any fuel not required under less stressful conditions (low speeds and loads) is returned to the tank unused

This circulatory type of system does not normally need bleeding as the system

is always operating above atmospheric pressure and full of fuel, preventing air getting into the system Leaks are easily noticed as fuel is normally forced out

of the system where they exist

Repairs to the low-pressure supply side of these systems do not normally mean that special bleeding procedures are required and as such, they are rarely fitted with a priming pump It is usually sufficient to switch on the

ignition or crank the engine to operate the feed pump and re-fill/bleed the system

Bleed points

Most systems incorporate bleed points between the priming pump and the engine-mounted high-pressure pump The valves operate in a similar way to those used in braking systems or household central heating systems They may be fitted to the filter, priming pump and the high-pressure fuel injection pump and in some cases, the bleed valves will be fitted with drainage pipes Vehicles with electric feed pumps may also be fitted with bleed valves

High pressure system

The high-pressure system includes all components and connections between the high-pressure pump and the injectors It is critical to effective engine operation that high pressure is maintained in this part of the fuel system at all times Bleed valves are not normally fitted in these areas

Bleeding the system

Once repairs have been carried out and the system is sealed, the following generalised procedure should enable the system to be purged of air

Pre-checks

Ensure the fuel tank has sufficient fuel to allow the engine to run

Check to see if the fuel system actually needs bleeding by attempting to start the engine – if it starts, allow it to idle for at least five minutes and then

gradually increase the engine revs If the engine accelerates to maximum rpm cleanly, it is not necessary to bleed the system If the engine does not run smoothly after ten minutes running, the fuel system probably needs

bleeding

It is always advisable to research the manufacturers’ own recommended procedures as some systems are notoriously difficult to purge of air and much time can be wasted if incorrect procedures are used

Bleeding procedure – vacuum type systems

Locate the priming pump and any bleed valves fitted between the pump and the engine

Operate the priming pump steadily, using the full stroke Initially there will be little resistance until the system between the tank and the pump is completely full of fuel, at which point the resistance will increase and the pump may appear to stop working

Open the bleed valve closest to the priming pump, keep a rag near the valve

to soak up any spillage or arrange a container to catch any fuel and continue pumping Close the valve when bubble-free fuel is seen escaping from the valve

Repeat step 3 for any other bleed valves in order, finishing at the one nearest the high-pressure fuel injection pump When you are sure that, the system is completely free of air attempt to start the engine and run it as in the previous pre-checks

Bleeding procedure – high-pressure system

If the engine does not start or runs roughly it may be because the

high-pressure part of the system also needs bleeding

Slacken all the fuel unions at the injectors by about one turn and use rags to prevent splashing Ensure the pipes are now loose; sometimes the pipes will remain sealed to the injectors even when the unions are loose

Use an assistant to crank the engine until substantial quantities of fuel are seen leaking from the unions and then tighten each union in turn

Be prepared for the engine to start Allow the engine to run as in the previous pre-checks section

Cleaning up any spillage on the engine will aid future leak detection

Progress check 1

Answer the following questions:

1 Name the three types of fuel filter most commonly fitted to light

vehicles?

2 Why should the fuel filler cap be removed before replacing a fuel filter?

3 What should be done to the filter bowl before refitting it after filter

replacement?

4 What commonly needs to be carried out after replacing a fuel filter?

Control Cable Adjustment

Most diesel fuel injection systems use a system of cables and linkages to connect the driver’s controls to the high-pressure fuel injection pump Some systems have cable-operated controls to stop the engine or to adjust the injection timing, fuelling and exhaust emissions As fuel injection systems become increasingly sophisticated, these controls will be gradually

superseded by electronic control systems although many of these may still incorporate mechanical linkages as well

Occasionally it may be necessary to adjust these cables, perhaps after repairs have been carried out or simply because wear has taken place The most common adjustment is carried out on the throttle cable and the following section covers this procedure It can be used as a basis for other cable

adjustments

Fuel injection pumps often have a number of externally accessible adjustment points including idle speed, fast idle (used when the engine is cold) and full throttle, no load speed The majority of these adjustments are factory-set by the pump manufacturer using specialised equipment not usually available in a vehicle workshop In normal service, most of these settings will remain fixed for the life of the pump

It is possible that over time, the idle speed setting will reduce and the full throttle speed setting increase due to constant “hammering” wear at contact points on the pump where the adjusting screws or linkages hit their stops Some of this wear can be accentuated by incorrect cable adjustment

Wear at these points may have a knock-on effect on the cable adjustments between the pump and the driver operated controls, resulting in symptoms such as variable idle speed, highlighted by varying under-bonnet temperature conditions or engine movement due to an over-tight throttle cable Cables may also need adjustment when they are disconnected or replaced

Pre-checks – throttle cable

If it is suspected that throttle cable adjustment is required, it is first necessary

to check the idle and full throttle engine speeds, under “no load” conditions Adjusting cables without carrying out these initial checks may result in further problems A tachometer is required for this check and a number of different types are available If fitted, the vehicle’s own rev counter may be used if it is considered accurate enough, although some manufacturers specify a

maximum speed to an accuracy of ± 25 RPM, which is difficult to determine

on most vehicle instruments

Always refer to the manufacturers’ procedures and specifications for the actual engine/vehicle involved The engine must be hot with all components such as the air cleaner and vacuum hoses fitted, correct valve clearances and injection timing and all Loads switched off with a neutral gear selected

Disconnect the accelerator cable at the fuel injection pump and start the engine Check that the idle speed is within specification and adjust if

necessary

Operate the pump lever manually to full throttle and compare the maximum speed with the manufacturers’ specifications Adjust the maximum speed if necessary

Do not be tempted to increase the maximum speed, which is set to ensure engine safety and acceptable exhaust emissions Allowing the lever further movement rarely increases engine power or speed without seriously

compromising these features

Cable adjustment

The most common cable adjustment routinely carried out on diesel engines is for the connection between the accelerator pedal and the fuel injection pump and this procedure is described below Routines for other cables use similar principles

The general aim for all types should be to provide full movement without applying excessive stress to the cable or linkage

Ensure that soundproofing material, mats and carpets are not fouling the accelerator pedal or linkages Ensure the accelerator pedal assembly is properly secured to the floor/bulkhead and the cable is connected correctly at both ends

Make sure that all springs and links are fitted properly and are not excessively worn

Replace the cable if it is frayed, sticking or if the outer sleeve is worn through Ensure that all clips/ties are in place to secure the cable throughout its length These should hold the cable in place without kinking, crushing or allowing it to contact moving/hot parts (pulleys, exhausts etc)

Some accelerator pedal assemblies incorporate a pedal height-limiting stop, which has the effect of adjusting the total movement of the cable If one is fitted, slacken this stop

Use an assistant to press the accelerator fully down without applying

excessive force Check that full throttle is achieved at the fuel injection pump without applying excessive stress to the cable If necessary, adjust the cable (adjustment methods will vary) to achieve full throttle without stressing the cable Ensure the adjuster is locked when the adjustment is completed

Release the accelerator pedal and check that the pump lever returns fully to the idle position, leaving a small amount of slack in the cable

If a pedal height adjuster is fitted, adjust it to take most of the slack out of the cable, leaving approximately 5mm of free play at the pedal pad (check

manufacturers’ specifications)

Start the engine and re-check the idle and the maximum, no load engine speeds

Drive belt adjustment

The high-pressure fuel injection pump may be driven from the engine

crankshaft using gears, roller chains or flexible, toothed rubber belts The pump is usually turned at half engine speed by its own, dedicated drive or by

a device, which drives other items as well, including the water pump, camshaft and accessories such as air-conditioning compressors Where belts are used

to drive multiple items, including the camshaft they are commonly referred to

as “cambelts” or “timing belts”

Whereas gears and chains rarely require adjustment during routine servicing, drive belts are much more susceptible to dirt/oil contamination and their failure often results in serious damage to the engine Accordingly, toothed belts need to be replaced at regular intervals as determined by the vehicle

manufacturer

Naturally, the belts require adjustment only when they are renewed and

although it is not normal practice to adjust used belts there may be occasions when a belt is removed and re-fitted as part of repairs to other components

In these cases, it may be acceptable to re-fit the old belt, adjusting it as

required

Toothed drive belts will usually stretch a small amount during service but unless they are over-tightened, they will not normally stretch enough to affect their operation

These belts do not need to be excessively tight as the teeth on the belt and pulleys drive the pulleys in a similar way to pairs of gear wheels As long as there is enough tension on the belt to ensure that the teeth remain engaged, that is normally sufficient Excessive tension may stretch the belt to a point where the distance between the teeth on the belt is different from the gaps between the teeth on the pulleys This is likely to lead to belt failure, which can have serious consequences for the engine so it is very important that the belt is not over-tightened, especially when a used belt is re-adjusted

Some manufacturers specify different tensions for used and new belts An over-tight timing belt is often noisy when the engine is running

Adjustment mechanisms

Manufacturers employ differing methods of adjustment for their engine timing belts, ranging from fully automatic hydraulic or spring-loaded devices to a simple tensioner pulley locked in position by a bolt The variations are almost endless and this makes it extremely important that the manufacturers’

information is consulted before attempting to adjust these belts Most belts are enclosed within a protective cover, which can be removed to gain access

to the adjusting mechanism

Timing errors

As the name suggests, a timing belt controls the relationship (timing) between the crankshaft, camshaft and high-pressure fuel injection pump pulleys When adjusting the tension of a timing belt it is extremely important that the relationship between these pulleys is maintained This is normally carried out

by aligning factory markings on the relevant pulleys when fitting the belt It is often the case that the timing marks on the pulleys have been correctly

aligned, but the timing on one or more teeth is out when the belt has been adjusted If this error is not spotted it can have consequences for the engine, ranging from poor fuel consumption and noise, to major engine failure

The main cause of this error is small amounts of slack left in the belt between some pulleys whilst the belt is being fitted With the belt properly located on the pulley teeth, the only slack in the belt should be on the belt “run”

containing the adjusting device between two pulleys when adjustment is carried out The following simple method will ensure this is always the case:

• ensure the adjuster mechanism is free to move, with any locking bolts loosened

• hold the crankshaft steady with its timing marks properly aligned

Some manufacturers recommend using a crankshaft-locking tool

The crankshaft and camshaft pulleys effectively split the length of most belts

in half, with the adjusting device between these pulleys on one side Using an appropriate tool, attempt to turn the camshaft pulley in whichever direction, will result in slight tension in the belt between the crankshaft and camshaft on the side without the tensioner

If this action results in the timing marks on either the camshaft or fuel injection pump pulley becoming mis-aligned, it will be necessary to remove the belt, re-align the marks and re-fit the belt, repeating the above procedure