Severe overheating of the engine can lead to deformation of the cylinder head and violation of the flatness of its mating surfaces (see below Cylinder head, item 2).
Cleaning
1. Scrape off all traces of the old gasket material and sealant from the mating surfaces of the cylinder head - try not to damage the surfaces.
The use of a special softener, which should be pre-saturated with adhering deposits, will greatly facilitate the work - ask in car accessories stores.
2. Remove all traces of scale from the walls of the water channels.
3. Thoroughly clean all accessible cavities and openings with a stiff wire brush. In case of severe contamination of the channels, head cleaning should be entrusted to specialists.
4. «Drive away» with a suitable tap for each of the bolt holes, removing corrosion products from the thread, traces of old sealant and restoring damaged turns. If you have access to a compressed air source, blow out the holes to remove chips and small debris.
Remember to wear protective goggles when using compressed air!
5. Use solvent and a brass wire brush to clean the combustion chambers of carbon deposits.
6. Wash the head with solvent and dry thoroughly. The use of compressed air will significantly reduce the drying time and will guarantee the quality of cleaning hard-to-reach cavities and holes.
Various kinds of compositions for removing traces of soot, which greatly facilitate the cleaning procedure, can be purchased at many car accessories stores. Remember that these types of products are usually chemically aggressive and must be used with appropriate precautions - strictly follow the manufacturer's instructions, usually listed on the container label.
7. On SOHC engines, flush the valve levers with solvent. Dry the components thoroughly with compressed air and fold them in an organized manner.
8. Solvent wash and dry tappets/hydraulic valve clearance compensators.
The use of compressed air will greatly facilitate the procedure (don't forget to wear safety glasses).
9. Wash in solvent and thoroughly dry the valve springs, their plates and split lock crackers - try not to mix up the components.
10. Scrape off the bulk of deposits formed on the valve surfaces, then with a wire nozzle to an electric drill, finally clean the surfaces of the valve stems and plates - make sure that the valves are not mixed up.
Status check
Carefully examine the condition of the cylinder head before deciding whether to remake the cylinder head. After reviewing the material presented in this subsection, make a list of components that need special attention.
Cylinder head
1. Carefully check the cylinder head for signs of coolant leaks, cracks or other damage. A cracked head must be replaced without fail. If there is no certainty in determining the condition of the head, it should be sent for verification to a car service workshop. If repair is not possible, replace the defective head.
2. Using a flatness gauge and a blade-type feeler gauge, check the head mating surface for signs of deformation. If the flatness exceeds the value allowed by the standards (see Specifications), the head must be sent to the groove in the mechanical workshop.
A - An assessment of the degree of flatness of the cylinder head is made along the diagonals of each of the mating surfaces
B - Cylinder head height is measured from mating surface to mating surface
A.
B.
One of the operating parameters of cylinder heads is their minimum allowable height (I) (mating surface to mating surface), which should not be reduced during machining (see Specifications).
3. Check the condition of the valve seats in each of the combustion chambers. In case of revealing cavities, cracks, traces of burnout, the head should be subjected to a special restorative repair, the implementation of which lies outside the qualifications of an average amateur mechanic and should be entrusted to car service specialists (Worn valve guides must first be replaced).
On 1.7L SOHC diesel engines, it is possible to replace valve seats.
4. Using a bore gauge, measure the inside diameter of the valve guide. After removing the gauge from the sleeve, it is measured with a micrometer. Also measure the outer diameter of the valve stem. Subtract the second measurement from the first measurement to determine the valve seat gap. Compare the received data with the requirements of the Specifications.
When using an inside gauge, insert it to the middle of the sleeve length, then move it up and down. Uneven resistance to movement of the meter indicates the presence of a taper bushing. If you are unsure when determining the condition of the components, do not hesitate to seek help from specialists.
5. Worn bushings must be replaced. Old bushings are knocked out into the combustion chambers with a punch. Before installation, new bushings should be cooled in the freezer, then pressed into the head drillings from the side of the camshaft to the prescribed standards (see Specifications) speaking level (if the data on the height of the protrusion of the guide sleeve is not given, seek advice from the specialists of the Opel branded workshop).
A sign of a loose seat in the valve guides is the appearance of blue smoke at the outlet of the exhaust system.
6. On diesel engines 1.7 l SOHC check for cracks and burnouts in the prechamber. Minor defects should not cause concern. Replacement of the chambers is required only in cases of deep burns, loss of original shape or loose fit in the head casting. If you are not sure about determining the condition of the prechambers, do not hesitate to seek help from specialists.
Valves
1. Carefully check the valve surfaces listed below for signs of uneven wear, deformation, cracks, cavities, and burn marks. Assess the degree of actuation of the valve stems. Check for cracks in the necks of the rods. Check the valves for bending by rotating them. Check for cavities and signs of excessive end wear. Identification of any of the listed defects requires the delivery of valves for refurbishment to a car service workshop.
1 - ends (liners) rods
2 - Grooves for the installation of crackers for split locks of plates
3 - Rods
4 - Working chamfers
5 - Exhaust valve
6 - Cylindrical part of the plate (belt)
7 - Inlet valve
2. Measure the width of the cylindrical part (girdle) plates of each of the valves. If the belt width is less than the specified value (see Specifications), replace the valve.
Valve springs
1. Assess the degree of wear of the end parts of each of the valve springs, check the springs for cavities. Using an angle gauge, determine the free length and check the trim of the valve springs. Compare measurement results with requirements (see Specifications), - if the spring is shorter than the lower permissible limit, it is sagging and must be replaced. Also check the forces developed by the springs for compliance with regulatory requirements (it is better to entrust this work to the specialists of the car service workshop). In the absence of confidence in determining the condition of the springs, it would be more correct to replace them.
2. On petrol engines 2.6 l SOHC the exhaust valve spring seats are equipped with rotators, which facilitate the freedom of rotation of the valves in the guide bushings. Turning manually, evaluate the condition of the rotators, in case of jerks and signs of biting, replace the defective components.
3. Check the spring plates and crackers of their split locks for cracks and signs of wear. All parts in doubtful condition should be replaced with new ones to avoid the development of defects in the future.
4. Camshafts, valve lifters and rocker arm assemblies with axles.
5. For a description of the procedures for checking the status of the listed components, see Removal, condition check and installation of components of a drive of valves. An assessment of the condition of the bearing journals of the camshafts must be made before the head is sent to a workshop for valve service. The presence of scratches, scoring and other mechanical defects on the necks of the head must be replaced regardless of the condition of the components of the valve mechanism. When servicing the SOHC engine, the condition of the valve rocker arms with axles should also be checked.
6. Replace any defective components found.
Lapping of valves
1. If the valve components are significantly worn, which is quite likely for an engine in need of overhaul, assemble the valve assemblies, install them in their regular places in the head, and proceed to the valve maintenance procedures.
2. If the external condition of the valves is found to be satisfactory, measure the diameters of their stems at several points with a micrometer. If there is a significant difference in results, the valve should be replaced.
3. For reliability of valves blocking access to the combustion chambers during engine operation, they should be ground in during installation. In addition, grinding allows you to get rid of minor defects in the mating surfaces. The necessary smoothness of the surface of the seats after their machining can only be achieved using fine-grained lapping pastes. Before using coarse pastes (in the presence of serious damage or burnout of the saddles) consult with experts - perhaps the only acceptable way out will be to replace the seat or valve.
4. Before lapping the valves, place the head on a workbench with the mating surface facing up.
5. Apply a small amount of lapping paste of the desired grit size to the surface of the valve seat, then attach the lapping tool suction cup to the outside of the valve disc. With a rotary motion, begin to rub the valve against the seat, lifting it from time to time in order to redistribute the paste. Installing a weak spring under the valve disc will help facilitate the task. When using coarse-grained pastes, try to achieve a dull matte surface of the lapped parts. After obtaining the desired result, clean the surfaces of the abrasive and repeat the lapping procedure using a fine-grained paste.
6. Lapping can be considered complete when an inseparable smooth matte ring appears on the working surfaces of the seat and plate. As soon as the desired result is achieved, grinding should be stopped.
7. After lapping all valves, remove all traces of abrasive and lapping paste with kerosene or thinner.
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