Cleaning and checking the condition of the cylinder head (Nissan Maxima A32)

A thorough cleaning of the cylinder head and valve train components followed by a detailed inspection of their condition will help determine the approximate scope of the upcoming restoration work.

Note: Severe engine overheating may result in deformation of the cylinder head and disruption of the flatness of its mating surfaces.

Cleaning

1. Scrape off all traces of old gasket material and sealant from the mating surfaces of the cylinder head, intake manifold and exhaust manifold - try not to damage the surfaces. The work will be significantly easier if you use a special softener, which should be pre-soaked into the adhering deposits - ask in car accessory stores.

2. Remove all traces of scale from the walls of the water channels.

3. Using a stiff wire brush, thoroughly clean all accessible cavities and openings. If the channels are heavily contaminated, head cleaning should be entrusted to specialists.

4. "Run" each of the bolt holes with a tap of the appropriate size, removing corrosion products and traces of old sealant from the threads and restoring damaged threads. If you have access to a source of compressed air, blow out the holes, removing chips and small debris from them.

Caution! When using compressed air, do not forget to wear safety glasses!

5. Using solvent and a brass wire brush, clean the combustion chambers from carbon deposits.

6. Wash the head with solvent and dry it thoroughly. Using compressed air will significantly reduce the drying time and will guarantee the quality of cleaning of hard-to-reach cavities and holes.

Note: Various types of carbon deposit removers, which make the cleaning process much easier, can be purchased at many car accessory stores. Remember that these types of products are usually chemically aggressive and should be used with appropriate precautions - strictly follow the manufacturer's instructions, usually on the container label.

7. On SOHC engines, solvent wash the rocker arm/shaft assemblies. Dry the components thoroughly with compressed air and stack them in an organized manner. Solvent wash and dry the valve lifters.

Note: Using compressed air will make this procedure much easier (don't forget to wear safety glasses).

8. Wash in solvent and thoroughly dry the valve springs, their plates and split lock crackers. Try not to mix up the components.

9. Scrape off the bulk of the deposits that have formed on the valve surfaces, then use a wire attachment on an electric drill to finally clean the surfaces of the valve stems and plates - make sure that the valves are not mixed up.

Checking the status

Note: Before deciding whether to machine the cylinder head, carefully examine its condition. After reviewing the material in this subsection, make a list of components that require special attention.

Cylinder head

1. Carefully check the cylinder head for signs of coolant leaks, cracks and other damage. A cracked head must be replaced. If you are not sure of the condition of the head, send it to a car service workshop for inspection. If repair is not possible, replace the defective head.





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2. Using a flatness gauge and a blade-type feeler gauge, check the mating surface of the head for signs of deformation. If the non-flatness exceeds the value permitted by the standards, (see Specifications), the head must be sent to a mechanical workshop for turning.

Note: One of the working parameters of cylinder heads is their minimum permissible height, which must not be reduced during mechanical processing.

3. Check the condition of the valve seats in each combustion chamber. If cavities, cracks, or burn marks are detected, the head should be subjected to special restorative repairs, the implementation of which is beyond the qualifications of the average amateur mechanic and should be entrusted to car service specialists.



4. Using a special bore gauge, measure the inside diameter of the valve guide bushing. After removing the gauge from the bushing, measure it with a micrometer. Also measure the outside diameter of the valve stem. In order to determine the clearance of the valve seat in the bushing, subtract the result of the second measurement from the result of the first measurement. Compare the obtained data with the requirements of the Specifications. Worn bushings are subject to replacement.

Note: When using a bore gauge, insert it to the middle of the bushing length, then move it up and down. Uneven resistance to movement of the gauge indicates the presence of taper in the bushing. If you are not sure when determining the condition of the components, do not hesitate to seek help from specialists.

Valves

1. Carefully inspect the working surfaces of the valves for signs of uneven wear, deformations, cracks, cavities and traces of burnout. Assess the degree of operation of the valve stems. Check for cracks in the necks of the stems. Check the valves for bending by rotating them. Make sure there are no cavities and signs of excessive wear on the ends. If any of the listed defects are detected, the valves must be delivered to a car service workshop for restoration.





2. Measure the width of the cylindrical part (band) of the valve disc for each valve. If the width of the band is less than the value specified in the Specifications, replace the valve.

Valve components

1. Assess the degree of wear of the end parts of each of the valve springs, check the springs for cavities. Measure the free length of the valve springs, compare the measurement results with the requirements of the Specifications. If the spring is shorter than the lower permissible limit, it is sagged and must be replaced. Also check the forces developed by the springs for compliance with the regulatory requirements (it is better to entrust this work to specialists at a car service workshop). If you are not sure about the condition of the springs, it would be better to replace them.



2. When installing each spring vertically on a flat surface, check the strictness of their trim. Springs with a violation of the trim, as well as sagging (see above), are subject to replacement.



3. Check the spring plates and split lock crackers for cracks and signs of wear. Any parts in questionable condition should be replaced with new ones to avoid future defects.

Camshafts, valve lifters and rocker arm assemblies with axles

1. A description of the procedures for checking the status of the listed components is given in Section Checking the condition of camshafts, valve lifters and bearings. The condition of the camshaft bearing journals should be assessed before the head is sent to the workshop for valve maintenance. If there are any scratches, scoring or other mechanical defects on the journals, the head must be replaced regardless of the condition of the valve train components. When servicing an SOHC engine, the condition of the valve drive rocker arms with axles should also be checked.

2. Replace all identified defective components.

3. If the valve components are significantly worn, which is quite likely for an engine that needs major repairs, assemble the valve assemblies and install them in their regular places in the head (see section Cylinder head assembly) and proceed to perform valve maintenance procedures (see section Valve maintenance).