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kap all phase & 6/11/03 11:35 am Page Student Workbook LV20 Engines (2) LV20/SWB Student Workbook for Technical Certificates in Light Vehicle Maintenance and Repair MODULE LV20 ENGINES (2) Contents Page Gaskets: Types of gasket Tightening down a cylinder head Exercise Seals Scroll type oil retainer Lip seal 3 9 11 Engine Valve Oil Seals: Exercise 13 14 Cam Belts: Checking the belt for serviceability Timing belt replacement (an example method) Timing belt components Removal Installing the cam belt Exercise 14 15 Valve Clearances: Adjusting valve clearances Example of an adjusting shim selection chart Four-Valve Diesel Engine Mechanism: Exercise 16 16 17 22 `31 32 34 ……… Page Engine Valve Timing 44 Decarbonising: Reasons for decarbonising engines Removing the valves Cleaning the cylinder head surface Removing carbon Cleaning the valve guides Degreasing the cylinder head Cleaning the valves Checking valve guides for wear Checking the valve for wear Removing worn valve guides Fitting new valve guides Use of a guide reamer Re-surfacing the valve seats Checking margin thickness Re-surfacing the valve stem Cutting the valve seats Checking the valve seat position Checking valve seat contact Lapping the valves Exercise 48 48 49 49 50 51 51 52 53 53 54 55 56 56 57 57 58 58 59 60 61 Lack of Compression: Testing methods 62 62 41 42 43 (Cont.) -1Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Page Cylinder leakage Exercise Oil consumption Oil burning and leaks 67 68 70 70 Engine Noises: Unusual and excessive noise Exhaust leaks Top of the engine Bottom of the engine Exercise Summary of main engine problems Engine failure 73 73 73 74 74 74 75 77 ……… -2Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Gaskets ‘O’ rings A selection of gaskets R bb 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 gasket chemicals are ‘job specific’ -3Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue 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 -4Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Compressible sections Cross-sections of a diesel engine cylinder head gasket showing reinforcement 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 -5Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue 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 A DTI (dial test indicator) is used to measure piston protrusion above the cylinder Valve cover Valve cover gasket 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 The gasket is made from an acrylic rubber, which excels in heat resistance and reliability -6Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue 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 not need to be retightened 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 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 Re-tighten another 90 degrees, check that the mark is 180 degrees i.e rearwards -7Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Exercise 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 Manifold side 0.05mm (0.0020 in.) 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 Maximum distortion: 0.05mm (0.0020 in.) If the distortion is greater than the maximum, replace the cylinder block -8Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue • 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 measurement (gap) Recommended action Seals Seals are used to keep fluids in but other contaminants and dirt out Seals are used between parts that have motion such as the crankshaft and 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 -9Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Cylinder leakage Regulated pressure enters the engine cylinder High cylinder leakage: checking valves, piston rings, cylinder bore and cylinder head gasket Within specification Air modulation knob used to zero gauge before use To engine ENGINE AIR LINE From air line High cylinder leakage Cylinder leakage is alternative way of determining the condition of the engine and provides a more accurate and full report than the compression test The main advantage of cylinder leakage testing is that diagnosis is more accurate, it ensures that engine requirements are made visible and an accurate assessment of the cost of the repair can be provided for the customer without dismantling the engine - 67 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Exercise Copy information from the appropriate slide into the table below: Statement Carrying out a wet compression test would confirm that the valves were leaking True/False Explanation Diesel engines rely on good compression pressure to raise the temperature of the air to ignite the fuel Cylinder leakage testing is a more precise method of fault diagnosis than the compression test - 68 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue How a cylinder leakage test should be carried out: • Remove the spark plugs • Ensure that the piston is at top dead centre (see setting tappets) • Screw the air supply pipe into No.1 spark plug hole, fit whistle to indicate when the piston is approaching TDC, rotate engine to TDC position both valves closed (compression) • Connect the gauge to air line pressure and adjust the modulator knob to zero the gauge • Connect the air feed pipe to the air supply pipe and allow air to enter the cylinder (take care that the piston is not forced down the cylinder due to the air pressure which should be about kg/cm² (70 psi) It may help to put the car in gear with the hand brake on (care must be taken) • Listen to where air is leaking from the following areas • Remove the oil filler cap and listen for air escaping, about 20% is allowed from here, this figure will vary depending upon engine size, more leakage is acceptable on larger engines Too much leakage means that the piston rings and cylinder bores may be worn There will always be leakage past the piston rings due to the piston ring gaps, take care not to wrongly diagnose worn bores and piston rings because of this slight leakage • Listen at the tail pipe, any leakage here means that the exhaust valve/s are leaking, no leakage is allowed past the exhaust valves • Listen at the intake manifold with the throttle valve held fully open, any leaks here means that the inlet valve/s are leaking, no leakage is allowed past the inlet valves • Check to see if any bubbles appear in the engine coolant by removing the radiator cap, it may be necessary to over fill the cooling system for this test Remember to remove the excess coolant after the test and to check the antifreeze mixture for correct strength Bubbles in the coolant means that the cylinder head gasket could be leaking or a crack has developed in the cylinder block or cylinder head • Rotate the engine and repeat the test on the remaining cylinders in correct firing order to avoid rotating the engine unnecessarily If a compression test has provided a suspect fault, the longer but more thorough cylinder leakage test may be carried out to clarify the fault - 69 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Oil consumption Oil burning and leaks Excessive oil consumption can be due to oil leaks or oil burning, oil leaks may only be present when the engine is running To locate oil leaks raise the vehicle on a vehicle lift and clean off the area that is showing an oil patch, this is usually the sump If necessary, clean off any traces of oil on the engine side, top and bottom Place a sheet of paper (newspaper or brown paper) under the vehicle and run the engine, note where the drops of oil appear, this will provide and indication as to the position of the oil leak Look above this position and then trace down to see where the oil first appears, the leak has been found! A slow leak follows the ribs of the cylinder block and is generally blown along the engine due to the forward motion of the vehicle Oil may be seeping past a worn crankshaft oil seal, this type of seal (lip seal) will only leak when the engine is running therefore oil will spray everywhere due to the spinning shaft Ultraviolet light Put on yellow glasses aim the UV light Look for the highest point of leakage Oil leaks Pinpointing some oil leaks can be difficult A method used, which makes things a little easier, is ultraviolet light leak detection which can be used for all fluid leaks A trace dye is used which is fluorescent, so under ultraviolet light (black light) it shows the leak up in an unmistakable yellow/green glow By aiming the light, a small dye stain will show the source of the leak Flexible and small UV lamps and improved trace dyes and the use of glasses with coated lenses have improved leak detection It is best to mix the dye with engine oil before adding oil to the engine - 70 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Safety first: Ensure that the vehicle cannot move, chock the wheels and keep your hands clear of moving parts and also wear a safety helmet, gloves and goggles Excessive oil consumption can also be attributed to oil burning This is caused by oil entering the cylinders and being burned Oil can enter the cylinders in several ways, such as: worn piston rings, scored cylinder walls, worn valve guides, seals and stems, worn turbocharger seals and blocked oil drain passages As a general rule and more noticeable during acceleration, an engine burning oil will emit blue smoke from the exhaust (black smoke if the engine is running too rich) Blocked oil-return passages at the top of the engine, from the valve mechanism down through the cylinder head to the cylinder block, can cause excessive oil consumption To check for this fault remove the oil filler cap and start the engine If the oil level rises steadily above the top of the valve guides, the drain passages are blocked These passages can be cleared of sludge but this can be taken as a good indication that the engine has been poorly maintained Clearing the passages will probably reduce oil consumption, but the engine may experience future problems To identify internal engine problems carry out a compression test or a cylinder leakage test to confirm whether the piston rings/cylinders are worn etc Loss of compression causes poor combustion and high consumption If the engine is turbocharged, carry out oil consumption tests previously described, then check if there is oil in the compressor housing or intake manifold, check the oil drain from the turbo housing to the cylinder block If the oil drain is restricted, oil will be forced under pressure into the engine Check the positive crankcase ventilation system (PCV) If the PCV valve does not close during ‘boost’ condition, the crankcase will be pressurised, this may force oil through the turbo oil drain passage into the turbo housing On fuel injection equipped engines, the oxygen sensor and catalytic converter may become contaminated with residues from the burning oil entering the exhaust system Using a four gas analyser can determine faults in exhaust emissions - 71 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Specific areas of oil loss summarised: • Timing cover or front cover oil seal, oil will blow rearwards • Cam box or rocker cover gasket, oil leaking down, the engine cylinder head and block • PCV valve malfunction causing pressure build up in the crankcase area which forces oil out of seals and gaskets External leaks and possible smoke may be identified • Worn rear main bearing crankshaft oil seal will cause external leaks that will have blown rearwards • Leaking valve stem oil seals or valve guide seals will cause exhaust smoke at idle and cold start (oil seeps into the engine cylinder during stationary periods then is burned when the engine is started) Blue oil emissions may be visible after prolonged deceleration then sudden acceleration • Worn piston oil control rings or blocked oil return holes in the piston will cause exhaust smoke on hard acceleration Cam cover and oil seals Rear main bearing oil seal Sump Timing cover Timing case oil seal Common areas of oil loss are shown in the above diagram Note: If oil is found on a cam belt then it must be replaced - 72 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Engine Noises Unusual and excessive noise Diagnosis of engine noise can be difficult, a stethoscope or a rubber hose can be a useful tool (a metal rod can also be used) that will help in locating where the noise is coming from, since the noise will travel through a hose or along a metal rod with ease Diagnosis of engine noise is nothing more than cutting the possibilities down to only one It is important to eliminate engine accessories such as those driven by the fan belt, alternators, air-conditioner compressor or power steering pump Removing the belt of belt driven accessories is a useful way of identifying if the noise is coming from any of these components Note: All diesel engines produce a ‘knocking’ sound when running (diesel knock) In a diesel engine fuel ignites when injected into the heated compressed air in the combustion chamber This rapid combustion causes very high pressures, which generate a rumble or dull clattering sound, this is normal Some types of fault within the fuel injection system cause the knocking noise to increase Exhaust leaks Blocking off the exhaust system momentarily increases the rate of ‘blow’ from the exhaust pipe The noise may be a severe blowing sound or, in the case of slight leaks, the exhaust may hiss while its exit is blocked Also check the exhaust manifold and any accessory connected to it, such as the oxygen sensor and exhaust gas re-circulating valve etc - 73 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Top of the engine Tappets are the most likely cause of noise from the top of the engine, incorrect clearances (too wide) are the most common fault but it is important not to rule out camshaft and valve lifter (cam follower) wear Bottom of the engine Noises from lower down in the engine are normally caused by worn big end bearings, which knock on over run and acceleration The noise reduces when the engine is lightly loaded Rumbling noises indicate that the main bearings are probably worn Big end bearing wear diagnosis is helped by the fact that it is accompanied by low oil pressure (use an oil pressure gauge to help diagnose the problem) Experience plays a large part in correct diagnosis of engine noise, which can only come with practice and having heard the noise first hand Exercise Copy information from the appropriate slide into the table below: Statement Worn big end bearings produce a light high frequency tapping sound True/False Explanation - 74 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Summary of main engine problems Cause Lack of power low compression Problem Remedy Burnt exhaust valves Remove cylinder head and replace valves Sticking and leaking valves Remove cylinder head and replace damaged valves Broken valve springs Check and renew Worn piston rings and cylinder bores Dismantle engine and renew piston rings, liners or rebore if permitted Leaking/blown cylinder head gasket Remove cylinder head check for distortion and replace gasket Problem Remedy Cause Leaking oil filter Leaking cam cover gasket Check oil filter for tightness, renew oil filter if necessary Inspect and fit new gasket Leaking timing case gasket Inspect and fit new gasket Leaking sump gasket Inspect and fit new gasket Oil leaks Leaking crankshaft pulley oil seal Leaking rear main bearing oil seal Inspect and fit new seal Inspect and fit new oil seal - 75 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Cause Problem Remedy Worn or missing valve stem oil seals Fit new oil seals Excessively worn valves and guides Fit new valves and guides Worn piston rings Fit new oil control rings Worn pistons and cylinder bores Re-bore if permitted, fit new cylinder liners or replace cylinder block Oil burning Large piston ring gaps Piston oil return holes blocked Cause Fit new piston rings De-carbonise engine, unblock return holes in piston Problem Remedy Worn valve mechanism (noisy tapping sounds from cam cover) Inspect and fit new valve operating gear as necessary Worn big end bearings (regular heavy knocking in crankcase) Remove the sump, clean out lubricating system, fit new bearings, reclaim crankshaft or fit new Engine noise Worn main bearings (rumbling and vibration) Worn timing gear/chain (rattling from front of engine) Remove sump, and crankshaft, fit new bearings, reclaim crankshaft or fit new, check oil pump and lubrication system Remove timing cover fit new gears or chain - 76 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Engine failure Cracked cylinder head between valves Bent valve Valve damaged piston - 77 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Broken valve spring Badly burnt and pitted valve seat - 78 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Valve removed Valve fatigue Piece of valve embedded in the cylinder head Damage to cylinder head due to piece of valve in cylinder Worn cam followers Worn and pitted camshaft lobes - 79 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Cause: connecting rod through the side of the cylinder bock Daylight can be seen through the hole in the cylinder block Damaged connecting rod and piston New piston New connecting rod - 80 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Scored crankshaft journal Burnt swirl chamber (diesel engine) - 81 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue ... Reserved LV20: Engines (2) Issue Install the timing belt guide correctly in this case with the cap side outwards - 26 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2). .. Reserved LV20: Engines (2) Issue Example of an adjusting shim selection chart Adjustingshim Adjusting selection selection - 41 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines. .. overhead camshaft engines One camshaft can be used to operate on engines with four valves per cylinder - 43 Copyright © Automotive Skills Limited 2003 All Rights Reserved LV20: Engines (2) Issue Engine