Nissan/Datsun 200SX/510/610/710/810/Maxima 1973-1984 Repair Guide

Valves

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REMOVAL & INSTALLATION



All Engines


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Fig. Fig. 1 Exploded view of the valve components (not all engines have double valve springs)



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Fig. Fig. 2 Use a valve spring compressor tool to relieve spring tension from the valve caps



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Fig. Fig. 3 A magnet may be helpful in removing the valve keepers



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Fig. Fig. 4 Remove the spring from the valve stem in order to access the seal



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Fig. Fig. 5 Once the spring has been removed, the O-ring may be removed from the valve stem



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Fig. Fig. 6 Remove the valve stem seal from the cylinder head



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Fig. Fig. 7 Invert the cylinder head and withdraw the valve from the cylinder head bore



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Fig. Fig. 8 Always install new valve stem seals

The cylinder head must be removed on all engines before the valves can be removed.

A valve spring compressor is needed to remove the valves and springs; these are available at most auto parts and auto tool shops. A small magnet is very helpful for removing the keepers and spring seats.

Set the head on its side on the bench. Install the spring compressor so that the fixed side of the tool is flat against the valve head in the combustion chamber, and the screw side is against the retainer. Slowly turn the screw in towards the head, compressing the spring. As the spring compresses, the keepers will be revealed; pick them off of the valve stem with the magnet as they are easily fumbled and lost. When the keepers are removed, slowly back the screw out and remove the retainers and springs. Remove the compressor and pull the valves out of the head from the other side. Remove the valve seals by hand and remove the spring seats with the magnet.

Since it is very important that each valve and its spring, retainer, spring seat and keepers is reassembled in its original location, you must keep these parts in order. The best way to do this is to cut either eight (four cylinder) or twelve (six cylinder) holes in a piece of heavy cardboard or wood. Label each hole with the cylinder number and either IN or EX, corresponding to the location of each valve in the head. As you remove each valve, insert it into the holder, and assemble the seats, springs, keepers and retainers to the stem on the labeled side of the holder. This way each valve and its attending parts are kept together, and can be put back into the head in their proper locations.

Oil each valve stem, and install each valve into the cylinder head in the reverse order of removal, so that all parts except the keepers are assembled on the stem. Always use new valve stem seals. Install the spring compressor, and compress the retainer and spring until the keeper groove on the valve stem is fully revealed. Coat the groove with a wipe of grease (to hold the keepers until the retainer is released) and install both keepers, wide end up. Slowly back the screw of the compressor out until the spring retainer covers the keepers. Remove the tool. Lightly tap the end of each valve stem with a rubber hammer to ensure proper fit of the retainers and keepers. Adjust the valves.

INSPECTION





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Fig. Fig. 9 Measure the valve stem diameter on the center of the stem



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Fig. Fig. 10 Use an inside dial indicator to measure the valve guide inside diameter (ID)



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Fig. Fig. 11 Critical valve dimensions. When the head has been worn to 0.020 in. margin thickness, replace the valve



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Fig. Fig. 12 A wire wheel may be used to clean the combustion chambers of carbon deposits



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Fig. Fig. 13 A dial gauge may be used to check valve stem-to-guide clearance

Before the valves can be properly inspected, the stem, lower end of the stem and the entire valve face and head must be cleaned. An old valve works well for clipping carbon from the valve head, and a wire brush, gasket scraper or putty knife can be used for cleaning the valve face and the area between the face and lower stem. Do not scratch the valve face during cleaning. Clean the entire stem with a rag soaked in thinners to remove all varnish and gum.

Thorough inspection of the valves requires the use of a micrometer, and a dial indicator is needed to measure the inside diameter of the valve guides. If these instruments are not available to you, the valves and head can be taken to a reputable machine shop for inspection. Refer to the Valve Specifications chart for valve stem and stem-to-guide specifications.

If the above instruments are at your disposal, measure the diameter of each valve stem at the locations illustrated. Jot these measurements down. Using the dial indicator, measure the inside diameter of the valve guides at their bottom, top and midpoint 90° apart. Jot these measurements down also. Subtract the valve stem measurement from the valve guide inside measurement; if the clearance exceeds that listed in the specifications chart under Stem-to-Guide Clearance, replace the valve(s). Stem-to-guide clearance can also be checked at a machine shop, where a dial indicator would be used.

Check the top of each valve stem for pitting and unusual wear due to improper rocker adjustment, etc. The stem tip can be ground flat if it is worn, but no more than 0.5mm can be removed; if this limit must be exceeded to make the tip flat and square, then the valve must be replaced. If the valve stem tips are ground, make sure you fix the valve securely into a jig designed for this purpose, so the tip contacts the grinding wheel squarely at exactly 90°. Most machine shops that handle automotive work are equipped for this job.

STEM-TO-GUIDE CLEARANCE



Valve stem-to-guide clearance should be checked upon assembling the cylinder head, and is especially necessary if the valve guides have been reamed or knurled, or if oversize valves have been installed. Excessive oil consumption often is a result of too much clearance between the valve guide and valve stem.

  1. Clean the valve stem with lacquer thinner or a similar solvent to remove all gum and varnish. Clean the valve guides using solvent and an expanding wire-type valve guide cleaner (a rifle cleaning brush works well here).
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  3. Mount a dial indicator so that the stem is at 90° to the valve stem and as close to the valve guide as possible.
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  5. Move the valve off its seat, and measure the valve guide-to-stem clearance by rocking the stem back and forth to actuate the dial indicator. Measure the valve stems using a micrometer and compare to specifications, to determine whether stem or guide wear is responsible for excessive clearance.
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