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Student Workbook

LV20 Engines (2)

kap all phase 2 & 3 6/11/03 11:35 am Page 1

Student Workbook for Technical Certificates in

Light Vehicle Maintenance and Repair

Scroll type oil retainer 9 Cleaning the cylinder head surface 49

Cleaning the valve guides 51

Checking valve guides for wear 53

Checking the belt for serviceability 15 Removing worn valve guides 54 Timing belt replacement (an example Fitting new valve guides 55

Timing belt components 16 Re-surfacing the valve seats 56

Installing the cam belt 22 Re-surfacing the valve stem 57

Checking the valve seat position 58

Adjusting valve clearances 34 Lapping the valves 60

Bottom of the engine 74

Summary of main engine problems 75

Gaskets

R bb

‘O’ rings

A selection of gaskets

Gaskets and seals are required in engines to ensure that the mating parts are snug, and to prevent liquids and gases from leaking, such as oil, petrol

coolant, exhaust etc

Types of gasket

Composite gaskets are combinations of cork, rubber, paper or felt, designed and cut specifically to individual applications They are often applied with gasket dressing or adhesive to aid assembly and sealing

Silicon gaskets (formed in place) are made of a silicone compound that is applied in an uncured blend, directly to the mating parts and allowed to cure in place after assembly

There are several types of sealant on the market Choose one that is most suitable, consider such things as ease of application, temperature range, pressure range and flexibility High temperature resistance and greater

flexibility are preferred for modern vehicles Silicon is a popular composite gasket sealant

Today’s high performance hot running engines require superior sealing and gasket products Engines have components of dissimilar metals with different expansion rates and can be very difficult to seal Engines are computer

controlled and require sophisticated sensors, which can be contaminated by improper chemical applications To meet the needs of high tech engines

The cylinder head gasket must seal between the surfaces of the cylinder head and block, preventing combustion pressure, oil or coolant escaping The engine expands and contracts with heating and cooling, making it easy for joints to leak, therefore the gaskets have to be soft and springy enough to adapt to expansion and contraction They also allow for irregularities in the mating parts

For many years a thin sheet of asbestos was used, which was sandwiched between two thin sheets of copper Most common now is the sheet steel type, which consists of a sheet of metal with corrugations formed around the holes

to make a good seal between combustion chambers, water holes and oil holes

Steel gaskets are usually coated with a lubricant, which allows for slight

gasket movement when tightening on fitting or during engine temperature variations, which cause unequal thermal expansion If the gasket has not been pre-treated then a thin film of oil or the use of a non-hardening lubricant should be used Correct tightening of the cylinder head is necessary to avoid the risk of distortion, which would cause the cylinder head gasket to ‘blow’ Cylinder heads must be tightened evenly and manufacturers’ specifications should be followed

Front

The gasket is laminated A shim has been added around the cylinder bore to increase the sealing surface, therefore increasing performance

Cross-sections of a diesel engine cylinder head gasket showing

To improve the durability of the cylinder head gasket and improve resistance

to leakage of combustion gases, reinforced compressible laminations are used Shown is a typical diesel cylinder head gasket

The thickness of the cylinder head gasket can be changed to alter the

compression ratio

Measuring the

amount of piston

protrusion above the

cylinder block for

correct selection of

cylinder head gasket

Measuring the

amount of piston

protrusion above the

cylinder block for

correct selection of

cylinder head gasket

The number of notches on the gasket identifies the correct selected gasket thickness based on the amount of protrusion of piston above the top of the cylinder

Valve cover

Valve cover gasket

A DTI (dial test indicator) is used to measure piston protrusion above the cylinder

The valve cover is a high strength aluminium die-cast alloy The gasket also includes a spark-plug gasket integrated to reduce the number of parts

Tightening down a cylinder head

There are two methods of tightening down a cylinder head In the first method all the bolts are tightened to finger tightness and then ‘pulled down’ using a torque wrench to the correct torque (elastic region) After the vehicle has covered 800 km the cylinder head should be re-tightened to the

recommended torque If the engine has an aluminium cylinder head then it should be tightened when cold, if it has a cast iron cylinder head then tighten when hot

Note: RTV (room temperature vulcanising) gaskets do not need to be tightened

re-The second method uses ‘torque to yield’, getting its name from the fact that bolts have an elastic limit known as the yield point This means that as the bolt is loaded beyond this limit but will not go back to its original size (plastic region) it will become permanently stretched after the load is removed Using the yield point of a bolt and going beyond this point provides a clamping effect

on the components Many manufacturers use this technique for highly

stressed bolts such as cylinder heads, crankshaft bearings, transmission and suspensions, these are common areas where this type of bolt is used

Cylinder head bolts are tightened in three progressive steps Apply a small amount of engine oil on the threads and under the bolt head before fitting Tighten the bolts in even passes and in sequence (see Phase 1 Engines LV06) to the recommended torque Mark the bolt head with chalk or paint etc Re-tighten the cylinder head bolts 90 degrees in the correct sequence

Exercise 1

Using a precision straight edge and feeler gauge, measure the surfaces

that come into contact with the cylinder block and manifolds for distortion.

Maximum distortion:

Cylinder block side 0.05mm (0.0020 in.) Manifold side 0.10mm (0.0039 in.)

If the distortion is greater than the maximum, replace the cylinder head

Using a precision straight edge and feeler gauge, measure the surfaces

that come into contact with the cylinder block and manifolds for distortion.

Maximum distortion:

Cylinder block side 0.05mm (0.0020 in.) Manifold side 0.10mm (0.0039 in.)

If the distortion is greater than the maximum, replace the cylinder head

Checking the surface of a cylinder head and block for distortion If required remove the cylinder head:

• Clean all mating parts thoroughly Excessive scraping can damage light alloy metals, therefore use a chemical gasket remover and flush all oily parts with residue free brake cleaner, or use a similar cleaner

• Using a straight edge and feeler gauge measure the gap between the feeler blade and the straight edge

Measure the surface which is in contact with the cylinder head gasket for

distortion in the same way as for the cylinder head.

Measure the surface which is in contact with the cylinder head gasket for

distortion in the same way as for the cylinder head.

• Carry out checks for distortion on various component surfaces e.g

thermostat housings, aluminium tappet covers and water pumps etc Place your results in the table below Discuss any issues with your tutor Look for signs of surface damage such as deep scratches or corrosion

Component Feeler gauge

camshaft of an engine If there is no relative motion then a gasket is used

Scroll type oil retainer

Scroll oil retainers are often fitted to either end of the crankshaft to prevent oil passing down the shaft The scroll consists of two methods of retaining oil, one method uses screw thread formed in the crankshaft and the second is a ring or fin known as a flinger ring These methods are used together

When oil reaches this ring it is flung off by centrifugal force as the shaft rotates and is caught in a cavity where it returns to the engine oil sump Behind the flinger ring is a screw type groove rather like a coarse screw thread Any oil that reaches the screw thread ‘scroll’ is wound back (wind back thread)

towards the flinger ring back into the sump

Oil flinger ring

Oil drain to sump

becoming blocked To carry out a repair the transmission and sump will usually require removing The engine will need to be removed on most

modern vehicles

Today’s vehicle manufacturers prefer the lip seal, which lends itself to

transverse engine configurations and transaxle arrangements (front engine front wheel drives)

service tool to prevent damage and the possibility of incorrect fitting

Steel shell

Garter spring

Crankcase

Synthetic rubber Lip

Shaft

Bearing

Close up view of a lip seal Examine the shaft before fitting a new seal It may have become ‘grooved’ due to wear, therefore a new seal would probably leak Although the seal is flexible, it may not be able to prevent oil leaks if the bearing has become worn

Removing and fitting lip oil seal using special service tools

Removing a lip seal using special tool

Fitting a new lip seal using special service tool

Engine Valve Oil Seals

Intake valve stem seal

is coloured brown

Exhaust valve stem seal is coloured black

Exhaust valve stem seal is coloured black

Some manufacturers mark the seals in some way to assist fitting if they are

different

Overhead valve mechanisms require oil seals to prevent oil from trickling down the valve stem or, in the case of the inlet valve, being drawn into the cylinder when the piston is on its induction stroke

Oil consumption and emissions become a main consideration as the valve stem and guide become worn over time Oil seals that have reached the end

of their serviceability, worn valve guides and stems can normally be detected

by allowing a warm engine to stand idle for a time, then starting the engine up and watching for blue smoke being emitted from the exhaust system when the engine speed is increased rapidly

Exercise 2

Copy information from the appropriate slide into the table below:

Cylinder head gaskets

prevent combustion gases,

coolant and oil leaking out

It is not necessary to

tighten all cylinder head

plastic region bolts to the

same tightness, because

they are more flexible and

will maintain an even

pressure between the

cylinder block and head

A lip seal is a unidirectional

seal

Oil consumption can be

remedied by fitting new

stem seals, this will

prevent blue smoke being

emitted from the exhaust

Some manufacturers use different methods of informing the technician that the seals are different for the exhaust and inlet valves It may be that the valves have different stem diameters

Never bend twist or turn the belt inside out

Never allow oil, water or other fluids to come into contact with the belt

Care of the belt:

• do not bend, twist or turn the belt inside out

Checking the belt for serviceability

Possible cause Timing belt problem

Check for correct

installation

Check the timing

cover and gasket for

Belt teeth cracked or damaged

Check the idler pulley

for nicks, check that

pulley is free to rotate

Cracks in belt or wear

Check the belt guide

and alignment of the

pulley

Wear or damage to one side of the belt

Check the timing

cover and gasket for

damage, check for

correct gasket

installation Check for

foreign material on

the belt teeth

Wear on belt teeth

Premature breaking

Premature breaking

Belt teeth damages or cracked

Belt teeth damages or cracked

Cracks or noticeable wear on belt face

Cracks or noticeable wear on belt face

Damage on side of the belt

Damage on side of the belt

Wear on belt teeth Wear on belt teeth

Timing belt replacement (an example method)

Timing belts become worn over time and manufacturers state a replacement mileage, which is normally in the region of 60,000 miles Although this may vary a little it’s a good target mileage and belts should be changed, otherwise there is a risk of severe engine damage (especially in diesel engines) due to belt slip or breakage

Timing belt components

The timing belt replacement procedure will differ depending upon the vehicle make and model An example of fitting a cam belt is demonstrated in the following text It is important that workshop manuals are used to ensure that correct procedures are followed

Removal

Set No.1 piston to TDC on its compression stroke

Turn the crankshaft pulley to align the groove with the mark ‘0’ on the timing belt case

Ensure that the valve lifters on the No.1 cylinder are able to rotate freely and that the valve lifters on No 4 cylinder cannot be rotated This will confirm that No.1 cylinder is at TDC compression If the valve lifters can turn on No 4 cylinder it means that this cylinder is at TDC compression

Setting up the engine before removing the cam belt will make the job easier when installing the new belt

Another point to note is that if the camshaft or the crankshaft is rotated when the belt is removed, damage may result to the valves and pistons due to

On some engines it is necessary to remove the engine mounting

Support for the engine, can be carried out by using a car jack It is important

to ensure that damage to the sump is avoided, and this can be done by using

a wooden block between the engine sump and the jack Do not use too much lift, only as much as is necessary is to support engine weight

Remove the three bolts and the engine mounting stay Remove engine

mounting and mounting insulator

Remove the crankshaft pulley using a special service tool to prevent the crankshaft turning while removing the securing bolt

The pulley can now be removed using a puller When the pulley becomes loose, support the pulley with one hand to prevent it from falling off

The timing belt cover can now be removed by removing the ten securing bolts

If the timing belt is to be used again then it must be marked by an arrow, which indicates the direction of rotation Also place match marks on the pulley and belt

Removing the belt involves loosening the pulley bolt and then pushing it as far

as it will go, temporarily tightening it, then removing the belt

Installing the cam belt

Ensure that No.1 cylinder is at TDC compression with both valves closed Using a wrench rotate the camshaft until the bearing cap mark and the centre

of the small hole on the camshaft pulley line up

At this stage ensure that the pulley is clean and free from oil and water

Ensure that the crankshaft is at TDC for No.1 by temporarily installing the pulley-mounting bolt and align the TDC marks on the oil pump body and the crankshaft pulley

When fitting the belt it is imperative that oil and water are prevented from coming into contact with it Keep the pulley clean Do not bend, twist or turn the belt inside out

If the belt is being refitted ensure that the marks put on the belt previously are used

Adjusting the tension of the cam belt Loosen the pulley and allow the tension

of the spring to push the pulley onto the belt

Temporarily install the pulley bolt and rotate the crankshaft clockwise, two revolutions from TDC to TDC

Be sure that both pulleys line up with the marks If the valve timing marks don’t line up then it will be necessary to repeat the procedure

Tighten the idler pulley mounting bolt, torque to manufacturers’

recommendations Remove the temporarily installed crank pulley bolt

Measure the timing belt tension (deflection) This measurement will vary depending upon the vehicle make and model If the measured value is not to manufacturers’ recommendations then re-adjust with the idler pulley

Install the timing belt guide correctly in this case with the cap side outwards

Install the belt cover

Install the crankshaft pulley on the crankshaft key groove Using the special service tool to hold the crankshaft pulley, tighten the bolt using a torque

wrench Cam belt removal and replacement differs between vehicle models and makes, therefore refer to the manufacturers’ instructions

This example can be taken as a good guide to fitting a cam belt, the main differences being timing mark location, number of items driven by the belt e.g camshafts, routing, special tools and torque settings

A typical diesel engine cam belt arrangement

The fuel injection timing would have to be set, along with the valve timing The pulleys are marked and the procedure is very similar to the previous example

The following figures indicate the main differences

Installing the cam belt

When reinstalling the cam belt ensure that direction of rotation and position marks are used

All pulleys must be free from oil, diesel fuel and water to prevent the belt becoming contaminated, which would shorten its life and put the engine in danger of being damaged due to premature failure of the belt

Carefully feeding the belt around the idler pulley

Carefully feeding the belt around the idler pulley

Place the belt carefully around the idler pulley Ensure correct alignment of the belt

The idler pulley bolt

is slackened off to allow tension to be applied to the belt

The idler pulley bolt

is slackened off to allow tension to be applied to the belt

The idler pulley is slackened off to allow spring tension to be applied to the cam belt

Rotating the crankshaft clockwise two revolutions from TDC to TDC

Rotating the crankshaft clockwise two revolutions from TDC to TDC

The crankshaft should be rotated two revolutions clockwise before checking the timing for correctness Never assume it is correct until this final check has been carried out

Remember to rotate the engine slowly to prevent damage to valves and

pistons due to incorrect timing

Checking that the pulleys align with the timing marks

Checking that the pulleys align with the timing marks

A final check must be made to ensure that the timing marks align If they do

Exercise 3

Copy information from the appropriate slide into the table below:

Cam belts are very

flexible and not affected

by oil, coolant or other

mark the direction of

rotation and place

matching marks on the

timing pulleys

On diesel engines it is

necessary to time the

power steering pump

along with the valve

timing

Valve Clearances

Valve clearances are necessary because the cylinder block, cylinder head, valves and valve mechanism expand when heated and contract when cooled The valve clearances are specified by the manufacturer They state whether the clearances should be measured with the engine hot or cold

Excessive clearance results in noisy operation and will lead to excessive wear

Too little clearance may result in the valve not closing properly under certain conditions This will lead to escape of gas through the exhaust valve, less seat contact and less heat dissipation through the seat, which may lead to burning of the exhaust valves, leading to loss of compression, power and uneven running

If the rate of expansion is greater in the valve mechanism than the cylinder head and block, the valve will not close completely Valve clearance is

provided to prevent this

For efficient engine operation valves should make an airtight fit when they are

in contact with their valve seats when closed If valve clearances are not maintained the performance of the engine suffers, it is therefore necessary to check and adjust the valve clearances periodically

Valve clearances may be checked when the engine is hot or cold depending upon the manufacturers’ recommendations, and the adjustment method also varies

Removing the valve cover

Normally valve mechanisms that use a screw adjustment and push rod

arrangement are checked and adjusted when the engine is hot More

common are the overhead cam type of mechanism, which is normally

adjusted when the engine is cold This is because the thermal expansion of the cylinder head is greater that the thermal expansion of the valves

Valve clearance

Adjusting valve clearances

The method of adjusting valve clearances using shims is explained,

(adjustment of valve clearances on engines using hydraulic tappets is not necessary)

Adjustment of valve clearances is carried out when the engine is cold

Set engine to TDC position Set engine to TDC position

Set No 1 cylinder to TDC (compression) by aligning the crankshaft pulley marks with the ‘0’ on the timing belt cover

Note: Removing the spark plugs makes it easier to rotate the engine

Checking that number 1 cylinder is on compression Checking that number 1 cylinder is on compression

Check that the valve lifters (cam followers) on No 1 cylinder can rotate freely, and that the valve lifters on cylinder No 4 will not rotate

Determine TDC compression position on rocker arm type valve mechanism by moving the rocker arms up and down

Determine TDC compression position on rocker arm type valve mechanism by moving the rocker arms up and down

A similar approach can be used for engines that use rocker arms to lift the valves

To check that No 1 cylinder is on TDC (compression), move the rocker arms

up and down (clearance) It is then safe to assume that correct engine

position has been achieved

An alternative method of determining TDC position of cylinder number 1

An alternative method of determining TDC position of cylinder number 1

Another way of achieving correct engine position is to use the distributor, if one is fitted Remove the distributor cap and check which of the segments (electrodes) points to No 1 cylinder via the plug lead, then check that the rotor arm is pointing to it This will verify that No 1 cylinder is at TDC

(compression)

The valve clearance check can now be carried out on the cylinders shown

The valve clearance check can now be carried out on the cylinders shown

In the example we will assume a valve clearance of 0.15 – 0.25 mm for the inlet valve and 0.20 – 0.30 mm for the exhaust valve

Methods of adjusting valve clearances will differ depending upon the make and model of vehicle, specifications will also differ, therefore it is essential that manufacturers’ data is sought before carrying out valve clearance adjustment

When the correct engine cylinder position has been achieved, the valves (shown shaded) can be checked and adjusted, e.g No 1 cylinder, inlet and exhaust valves, No 2 cylinder inlet valves and No 3 exhaust valves

Checking the valve (tappet) clearance

Checking the valve (tappet) clearance

Insert a feeler gauge between the camshaft and the valve lifter to establish the clearance If the clearance is correct the gauge will fit with just slight

resistance as it is moved to and fro in the gap

If the clearance is too small or too large, identify the difference between the recommended clearance and the one measured, record the measurement

Adjusting the remaining valves (rotate the engine 360 degrees

Rotate the engine 360 degrees ensuring that the mark on the pulley aligns with the ‘0’ mark on the timing belt cover, this action will bring No 4 cylinder to TDC (compression) the remaining valve clearances can now be checked following the earlier procedure

Remove the adjusting shim using a small screwdriver and a magnetic finger

Measuring shim thickness with a micrometer

Using a micrometer, measure the thickness of the shim that has been

removed and calculate the thickness of the new shim, so that the correct clearance can be achieved

T = Thickness of the shim

A = Measured valve clearance

S = Specific valve clearance

N = Thickness of new shim

N = T + (A – S)

Select a shim that is as close to the calculated value as possible