Cylinder head - dismantling, cleaning, inspection and assembly
Note: New and reconditioned cylinder heads will be available from the original manufacturer, and from engine overhaul specialists. It should be noted that some specialist tools are required for the dismantling and inspection procedures, and new components may not be readily available. It may, therefore, be more practical and economical for the home mechanic to purchase a reconditioned head, rather than to dismantle, inspect and recondition the original head.
1 Remove the cylinder head from the engine block and separate the inlet and exhaust manifolds from it, as described in Part A of this Chapter.
2 Refer to Chapter 3 and remove the thermostat housing together with its O-ring (see illustration). Where applicable, unscrew the coolant temperature sensor and oil pressure switch from the cylinder head.
4.2 Remove the thermostat housing together with its O-ring (arrowed)
3 Refer to Chapter 2A and remove the timing belt sprocket from camshaft.
4 Remove the spark plugs (Chapter 1).
5 Remove the distributor (Chapter 5B).
6 It is important that groups of components are kept together when they are removed and, if they are still serviceable, refitted in the same groups, If they are refitted randomly, accelerated wear leading to early failure will occur. Stowing groups of components in plastic bags or storage bins will help to keep everything in the right order - label them according to their fitted location, e.g. ‘No 1 exhaust’, ‘No 2 inlet’ , etc (see illustration).
(Note that No 1 cylinder is nearest the timing belt end of the engine.)
4.6 Keep groups of components together in labelled boxes or bags
7 Check that the manufacturers identification and orientation markings are visible on camshaft bearing caps; if none can be found, make your own using a scriber or centre punch.
8 The camshaft bearing cap retaining nuts must be removed progressively and in sequence to avoid stressing the camshaft, as follows.
9 Slacken the nuts from bearing caps Nos 5, 1 and 3 first, then at bearing caps 2 and 4, slacken the nuts alternately and diagonally half a turn at a time until they can be removed by hand. Note: Camshaft bearing caps are numbered 1 to 5 from the timing be/t end.
10 Slide the oil seal from the timing sprocket end of the camshaft and discard it as a new item must be used on reassembly.
11 Carefully lift the camshaft from the cylinder head - do not allow it to tilt. Support both ends as it is removed so that the journals and lobes are not damaged.
12 Lift the hydraulic tappets from their bores and store them with the valve contact surface facing downwards, to prevent the oil from draining out. Make a note of the position of each tappet, as they must be fitted to the same valves on reassembly - accelerated wear leading to early failure will result if they are interchanged.
13 Turn the cylinder head over and rest it on one side. Using a valve spring compressor, compress each valve spring in turn, extracting the split collets when the upper valve spring seat has been pushed far enough down the valve stem to free them. If the spring seat sticks, lightly tap the upper jaw of the spring compressor with a hammer to free it.
14 Release the valve spring compressor and remove the upper spring seat, valve spring(s) and lower spring seat. Note: Depending on age and specification, engines may have concentric double valve springs, or single valve springs with no lower spring seat.
15 Use a pair of long-nosed pliers to extract the valve stem oil seal and withdraw the valve itself from the head gasket side of the cylinder head. If the valve sticks in the guide, carefully deburr the end face with fine abrasive paper.
Repeat this process for the remaining valves.
16 Using a suitable degreasing agent, remove all traces of oil deposits from the cylinder head, paying particular attention to the journal bearings, hydraulic tappet bores, valve guides and oilways. Scrape off any traces of old gasket from the mating surfaces, taking care not to score or gouge them. If using emery paper, do not use a grade of less than 100. Turn the head over and using a blunt blade, scrape any carbon deposits from the combustion chambers and ports.
Caution: Do not erode the sealing surface of the valve seat. Finally wash the entire head casting with a suitable solvent to remove the remaining debris.
17 Clean the valve heads and stems using a fine wire brush. If the valve is heavily coked, scrape off the majority of the deposits with a blunt blade first, then use the wire brush.
Caution: Do not erode the sealing surface of the valve face.
18 Thoroughly clean the remainder of the components using solvent and allow them to dry completely. Discard the oil seals, as new items must be fitted when the cylinder head is reassembled.
Cylinder head casting
19 Examine the head casting closely to identify any damage sustained or cracks that may have developed. Pay particular attention to the areas around the mounting holes, valve seats and spark plug holes. If cracking is discovered between the valve seats, or between the valve seats and spark plug threads Volkswagen state that the cylinder head may be reused, provided the cracks are no larger than 0.5 mm wide or that no more than the first spark plug thread is cracked.
More serious damage will mean the renewal of the cylinder head casting.
20 Moderately pitted and scorched valve seats can be repaired by lapping the valves in during reassembly, as described later in this Chapter. Badly worn or damaged valve seats may be restored by recutting ; this is a highly specialised operation involving precision machining and accurate angle measurement and as such should be entrusted to a professional cylinder head re-builder.
21 Measure any distortion of the gasketed surfaces using a straight edge and a set of feeler blades. Take one measurement longitudinally on both the inlet and exhaust manifold mating surfaces. Take several measurements across the head gasket surface, to assess the level of distortion in all planes (see illustration). Compare the measurements with the figures in the Specifications. If the head is distorted out of specification, it may be possible to repair it by smoothing down any high-spots on the surface with fine abrasive paper.
4.21 Checking for cylinder head distortion using a straight edge and a set of feeler blades
22 Minimum cylinder head heights (measured between the cylinder head gasket surface and the cylinder head cover gasket surface), where quoted by the manufacturer, are listed in Specifications. If the cylinder head is to be professionally machined, bear in mind the following (see illustrations):
4.22a Minimum cylinder head height (a)
4.22b Minimum distance (a) between top of valve guides and upper surface of cylinder head
a) The minimum cylinder head height dimension (where specified) must be adhered to.
b) The valve seats will need to be recut to suit the new height of the cylinder head, otherwise valve to piston crown contact may occur.
c) Before the valve seats can be recut, check that there is enough material left on the cylinder head to allow repair; if too much material is removed, the valve stem may protrude too far above the top of the valve guide and this would prevent the hydraulic tappets from operating correctly. Refer to a professional head rebuilder or machine shop for advice.
Note: Depending on engine type, it may be possible to obtain new valves with shorter valve stems - refer to your VW dealer for advice.
23 The camshaft is identified by means of markings stamped onto the side of the shaft, between No 1 cylinder inlet and exhaust lobes.
24 Visually inspect the camshaft for evidence of wear on the surfaces of the lobes and journals. Normally their surfaces should be smooth and have a dull shine; look for scoring, erosion or pitting and areas that appear highly polished - these are signs that wear has begun to occur. Accelerated wear will occur once the hardened exterior of the camshaft has been damaged, so always renew worn items. Note: If these symptoms are visible on the tips of the camshaft lobes, check the corresponding hydraulic tappet, as it will probably be worn as well.
25 Examine the distributor drive gear for signs of wear or damage. Slack in the drive caused by worn gear teeth will affect ignition timing.
26 If the machined surfaces of the camshaft appear discoloured or ‘blued’, it is likely that it has been overheated at some point, probably due to inadequate lubrication. This may have distorted the shaft, so check the runout as follows: rotate the camshaft between two V - blocks and using a DTI gauge, measure the runout at the centre journal Compare this with the Specifications. If it exceeds this figure, camshaft renewal should be considered.
27 To measure the camshaft endfloat, temporarily refit the camshaft to the cylinder head, then fit the third bearing cap and tighten the fixings to the specified first stage torque setting - refer to Reassembly for details.
Anchor a DTI gauge to the timing pulley end of the cylinder head and align the gauge probe with the camshaft axis. Push the camshaft to one end of the cylinder head as far as it will travel, then rest the DTI gauge probe on the end of the camshaft and zero the gauge display. Push the camshaft as far as it will go to the other end of the cylinder head and record the gauge reading. Verify the reading by pushing the camshaft back to its original position and checking that the gauge indicates zero again. Note: The hydraulic tappets must not be fitted to the cylinder whilst this measurement is being taken.
28 Check that the camshaft endfloat measurement is within the limit listed in Specifications.
Wear outside of this limit is unlikely to be confined to any one component, so renewal of the camshaft, cylinder head and bearing caps must be considered; seek the advice of a cylinder head rebuilding specialist.
29 The difference between the outside diameters of the camshaft bearing surfaces and the internal diameters formed by the bearing caps and the cylinder head must now be measured, this dimension is known as the camshaft “running clearance”.
30 The dimensions of the camshaft bearing journals are not quoted by the manufacturer, so running clearance measurement by means of a micrometer and a bore gauge or internal vernier calipers cannot be recommended in this case.
31 Another (more accurate) method of measuring the running clearance involves the use of Plastigage. This is a soft, plastic material supplied in thin “sticks” of about the same diameter as a sewing needle. Lengths of Plastigage are cut as required, laid on the camshaft bearing journals and crushed as the bearing caps are temporarily fitted and tightened. The Plastigage spreads widthways as it is crushed; the running clearance can then be determined by measuring the increase in width using the card gauge supplied with the Plastigage kit.
32 The following paragraphs describe this measurement procedure step by step, but note that a similar method is used to measure the crankshaft running clearances; refer to the illustrations in Section 10 for further guidance.
33 Ensure that the cylinder head, bearing cap and camshaft bearing surfaces are completely clean and dry. Lay the camshaft in position in the cylinder head.
34 Lay a length of Plastigage on top of each of the camshaft bearing journals.
35 Lubricate each bearing cap with a little silicone release agent, then place them in position over the camshaft and tighten the retaining nuts down to the specified first stage torque setting only - refer to Reassembly later in this Section for guidance. Note: Do not rotate the camshaft whilst the bearing caps are in place, as the measurements will be affected.
36 Carefully remove the bearing caps again, lifting them vertically away from the camshaft to avoid disturbing the Plastigage. The Plastigage should remain on the camshaft bearing surface, squashed into a uniform sausage shape. If it disintegrates as the bearing caps are removed, re-clean the components and repeat the exercise, using a little more release agent on the bearing cap.
37 Hold the scale card supplied with the kit against each bearing journal and match the width of the crushed Plastigage with the graduated markings on the card, use this to determine the running clearances.
38 Compare the camshaft running clearance measurements with those listed in the Specifications; if any are outside the specified tolerance, the camshaft and cylinder head should be renewed.
39 On completion, remove the bearing caps and camshaft and clean of all remaining traces of Plastigage and silicone release agent.
Valves and associated components
Note: On all engines, the valve heads cannot be re-cut (although they may be lapped in); new or exchange units must be obtained.
40 Examine each valve closely for signs of wear. Inspect the valve stems for wear ridges, scoring or variations in diameter; measure their diameters at several points along their lengths with a micrometer (see illustration).
4.40 Measure the diameters of the valve stems at several points along their lengths using a micrometer
41 Check the overall length of each valve and compare the measurements with the figure in the Specifications.
42 The valve heads should not be cracked, badly pitted or charred. Note that light pitting of the valve head can be rectified by lappingin the valves during reassembly, as described later in this Section.
43 Check that the valve stem end face is free from excessive pitting or indentation; this would be caused by defective hydraulic tappets.
44 Place the valves in a V - block and using a DTI gauge, measure the runout at the valve head. A maximum figure is not quoted by the manufacturer, but the valve should be renewed if the runout appears excessive.
45 Insert each valve into its respective guide in the cylinder head and set up a DTI gauge against the edge of the valve head. With the valve end face flush with the top of the valve guide , measure the maximum side to side deflection of the valve in its guide (see illustration). If the measurement is out of tolerance, the valve and valve guide should be renewed as a pair. Note: Valve guides are an interference fit in the cylinder head and their removal requires access to a hydraulic press.
For this reason, it would be wise to entrust the job to an engineering workshop or head rebuilding specialist.
4.45 Measuring the deflection of a valve in its guide
46 Using vernier callipers, measure the free length of each of the valve springs. As a manufacturer’s figure is not quoted, the only way to check the length of the springs is by comparison with a new component. Note that valve springs are usually renewed during a major engine overhaul.
47 Stand each spring on its end on a flat surface, against an engineers square. Check the squareness of the spring visually; if it appears distorted, renew the spring.
48 Measuring valve spring pre-load involves compressing the valve by applying a specified weight and measuring the reduction in length.
This may be a difficult operation to conduct in the home workshop, so it would be wise to approach your local garage or engineering workshop for assistance. Weakened valve springs will at best, increase engine running noise and at worst, cause poor compression, so defective items should be renewed.
Caution: Unless all new components are to be used maintain groups when refitting valve train components - do not mix components between cylinders and ensure that components are refitted in their original positions.
49 To achieve a gas tight seal between the valves and their seats, it will be necessary to grind, or ‘lap’, the valves in. To complete this process you will need a quantity of fine/coarse grinding paste and a grinding tool - this can either be of the dowel and rubber sucker type, or the automatic type which are driven by a rotary power tool.
50 Smear a small quantity of fine grinding paste on the sealing face of the valve head.
Turn the cylinder head over so that the combustion chambers are facing upwards and insert the valve into the correct guide.
Attach the grinding tool to the valve head and using a backward/forward rotary action, grind the valve head into its seat. Periodically lift the valve and rotate it to redistribute the grinding paste (see illustration).
4.50 Grinding in a valve
51 Continue this process until the contact between valve and seat produces an unbroken, matt grey ring of uniform width, on both faces. Repeat the operation for the remaining valves.
52 If the valves and seats are so badly pitted that coarse grinding paste must be used, check first that there is enough material left on both components to make this operation worthwhile - if too little material is left remaining, the valve stems may protrude too far above their guides, impeding the correct operation of the hydraulic tappets. Refer to a machine shop or cylinder head rebuilding specialist for advice.
53 Assuming the repair is feasible, work as described in the previous paragraph but use the coarse grinding paste initially, to achieve a dull finish on the valve face and seat. Then, wash off coarse paste with solvent and repeat the process using fine grinding paste to obtain the correct finish.
54 When all the valves have been ground in, remove all traces of grinding paste from the cylinder head and valves with solvent and allow them to dry completely.
55 Turn the head over and place it on a stand, or wooden blocks. Leave enough room underneath to allow the valves to be inserted.
56 Working on one valve at a time, lubricate the valve stem with clean engine oil and insert it into the guide. Fit one of the protective plastic sleeves supplied with the new valve stem oil seals over the valve end face - this will protect the oil seal whilst it is being fitted (see illustrations).
4.56a Fitting a valve into its guide
4.56b Fitting a protective plastic sleeve over the valve end face
57 Dip a new valve stem seal in clean engine oil and carefully push it over the valve and onto the top of the valve guide - take care not to damage the stem seal as it passes over the valve end face. Use a suitable long reach socket to press it firmly into position (see illustration).
4.57 Pressing a new valve stem oil seal into position using a long reach socket
58 Locate the valve spring(s) over the valve stem. Where a lower spring seat is fitted, ensure that the springs locate squarely on the stepped surface of the seat (see illustrations). Note: Depending on age and specification, engines may have either concentric double valve springs, or single valve springs with no lower spring seat.
4.58 Fitting the inner valve spring
4.58 Fitting the outer valve spring
59 Fit the upper seat over the top of the springs, then using a valve spring compressor, compress the springs until the upper seat is pushed beyond the collet grooves in the valve stem. Refit the split collet, using a dab of grease to hold the two halves in the grooves (see illustration).
Gradually release the spring compressor, checking that the collet remains correctly seated as the spring extends. When correctly seated, the upper seat should force the two halves of the collet together and hold them securely in the grooves in the end of the valve.
4.59 Spring seat being fitted over the tops of the valve springs
60 Repeat this process for the remaining sets of valve components. To settle the components after installation, strike the end of each valve stem lightly with a mallet, using an interposed block of wood to protect the stem from damage. Check before progressing any further that the split collets remain firmly held in the end of the valve stem by the upper spring seat.
61 Smear some clean engine oil onto the sides of the hydraulic tappets and fit them into position in their bores in the cylinder head.
Push them down until they contact the valves, then lubricate the camshaft lobe contact surfaces (see illustration).
4.61 Refitting the hydraulic tappets
62 Lubricate the camshaft and cylinder head bearing journals with clean engine oil, then carefully lower the camshaft into position on the cylinder head. Support the ends of the shaft as it is inserted, to avoid damaging the lobes and journals (see illustration).
4.62 Lowering the camshaft into position
63 Oil the upper surfaces of the camshaft bearing journals, then fit the bearing caps in place. Ensure that they are fitted the right way around and in the correct locations, then fit and tighten the retaining nuts, as follows:
64 The bearing caps have their respective cylinder numbers stamped onto them and have an elongated lug on one side. When correctly fitted, the numbers should be readable from the exhaust side of the cylinder head and the lugs should face the inlet side of the cylinder head (see illustration).
4.64 Camshaft bearing cap markings and orientation
65 Fit caps Nos 2 and 4 over the camshaft and tighten the retaining nuts alternately and diagonally to the specified first stage torque (see illustration).
4.65 Tightening the camshaft bearing cap nuts
66 Smear the cylinder head mating surfaces of caps Nos 1 and 5 with suitable sealant then fit them, together with cap No 3, over the camshaft and tighten the nuts to the specified first stage torque.
67 Tighten all bearing caps to the second stage torque, then fit the bolts to bearing cap No 5 and tighten them to the specified torque.
68 With reference to Chapter 2A lubricate the lip of a new camshaft oil seal with clean engine oil and locate it over the end of the camshaft. Using a mallet and a long reach socket of an appropriate diameter, drive the seal squarely into its housing until it bears against the inner stop - do not attempt to force it in any further.
69 Refit the coolant outlet elbow, using a new gasket/O-ring as necessary. Tighten the retaining bolts securely.
70 Refit the coolant sensor and oil pressure switch, using new sealing washers as appropriate (see illustration).
4.70 Refitting the oil pressure switch
71 With reference to Chapter 2A, carry out the following (see illustration):
4.71 Refitting the camshaft sprocket and bolt
a) Refit the timing belt sprocket to the camshaft.
b) Refit the inlet and exhaust manifolds, complete with new gaskets.
72 Refer to Chapter 2A or B as applicable refit the cylinder head to the cylinder block.
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