Nissan Pick-ups and Pathfinder 1989-1995

Valves

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REMOVAL & INSTALLATION



See Figures 1, 2, 3 and 4

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



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Fig. Fig. 1: A small magnet makes valve spring keeper removal much easier



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Fig. Fig. 2: After compressing the valve spring lift out the valve keepers or valve collets



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Fig. Fig. 3: Removing the valve spring and retainer with the tool still attached



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Fig. Fig. 4: Remove the valve seal after the valve spring assembly is removed

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, since they are easily fumbled and lost. After the keepers are removed, back the screw out then 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, spring, retainer, seat and keeper is reassembled in its original location, you must keep these parts in order. The best way to do this to 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.

After lapping each valve into its seat, oil each valve stem, and install each valve into the 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.

INSPECTION



See Figures 5, 6, 7 and 8

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 chipping carbon from the valve head. 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 ship for inspection. Refer to the Valve Specifications chart for valve stem and stem-to-guide specifications.

Measure the diameter of each valve stem at the correct locations. 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.



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Fig. Fig. 5: Use a dial indicator to check valve guide deflection



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Fig. Fig. 6: Checking the stem-to-guide clearance



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Fig. Fig. 7: Critical valve dimensions



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Fig. Fig. 8: Check the valve seat concentricity with a dial indicator

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 0.020 in. (0.50mm) 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 to be ground, make sure you secure the valve in 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.

REFACING



See Figure 9

Valve refacing should only be handled by a reputable machine shop, as the experience and equipment needed to do the job are beyond that of the average owner/mechanic. During the course of a normal valve job, refacing is necessary when simply lapping the valves into their seats will not correct the seat and face wear. When the valves are reground (resurfaced), the valve seats must also be recut, again requiring special equipment and experience.



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Fig. Fig. 9: Valve seat width and centering

VALVE LAPPING



See Figures 10 and 11

Because of the precision machining and the improved quality of material used in today's engines (hardened valves and seats), valve lapping is often not necessary or possible. To be sure, always check with the machine shop which has performed any valve seat work on your cylinder head and follow their recommendation. If valve lapping is necessary use this procedure as a general guide. Set the cylinder head on the workbench, combustion chamber side up. Rest the head on wooden blocks on either end, so there are two or three inches between the tops of the valve guides and the bench.



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Fig. Fig. 10: Lapping the valves by hand



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Fig. Fig. 11: Home-made valve lapping tool

  1. Lightly lubricate the valve stem with clean engine oil. Coat the valve seat completely with valve grinding compound. Use just enough compound that the full width and circumference of the seat are covered.
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  3. Install the valve in its proper location in the head. Attach the suction cup end of the valve lapping tool to the valve head. It usually helps to put a small amount of saliva into the suction cup to aid in sticking it to the valve.
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  5. Rotate the tool between the palms, changing position and lifting the tool often to prevent grooving. Lap the valve until a smooth, evenly polished seat and valve face are evident.
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  7. Remove the valve from the head. Wipe away all traces of grinding compound from the valve face and seat. Wipe out the port with a solvent soaked rag, and swab out the valve guide with a piece of solvent soaked rag to make sure there are no traces of compound grit inside the guide. This cleaning is important.
  8.  
  9. Proceed through the remaining valves, one at a time. Make sure the valve faces, seats, cylinder ports and valve guides are clean before reassembling the valve train.
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