Nissan Sentra/Pulsar/NX 1982-1996 Repair Guide

Valves and Springs

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REMOVAL & INSTALLATION



See Figures 1, 2, 3 and 4



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Fig. Fig. 1: Compressing the valve spring-E-Series engine shown



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Fig. Fig. 2: Disassembly of the valve mechanism-CA16DE and CA18DE engines shown



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Fig. Fig. 3: Disassembly of the valve mechanism-GA16i engine shown



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Fig. Fig. 4: Disassembly of the valve mechanism-SR20DE engine shown

The aluminum heads used on these Nissan cars require several special tools and extreme accuracy for disassembly, measurements and assembly. The procedures provided will guide you through a basic disassembly and inspection. If any cylinder head service is needed, it is recommend you take the cylinder head to a qualified machine shop. The specialize training and tools provided by the machine shop should save you time and money in the long run.

If just removing the valve spring, the cylinder head does not have to be removed from the engine. Using a spark plug hole adapter, pressurize the cylinder with compressed air so the valve will not fall into the cylinder.

  1. Refer to the Cylinder Head removal and installation procedures in this section and remove the cylinder head.
  2.  
  3. Loosen and back off the rocker arm adjusting screws, then remove the rocker arm assembly.
  4.  

After removing the rocker arm assembly, remove the spring retainers and the rocker arms from the shaft(s) (be sure to keep the parts in order), then reinstall the rocker arm shaft.

  1. Using the spring compression tool KV101072S0 or equivalent, compress the valve springs. Remove the valve keeper, then relieve the spring pressure. Remove the springs, the valve seals and the valves.
  2.  

To install:
  1. Use new oil seals and check the valve guide for excessive side to side movement. Tighten the rocker shaft bolts to 14-18 ft. lbs. (19-24 Nm), in a circular sequence. Adjust the valves as outlined in Engine Electrical .
  2.  

The intake/exhaust valve springs are the uneven pitch type. That is, the springs have narrow coils at the bottom and wide coils at the top. The narrow coils (painted white) must be the side making contact on the cylinder head surface.

After the cylinder head is removed from the engine, on the Pulsar CA16DE and CA18DE engines, remove the camshaft sprockets, tensioner pulley and rear cover. Then remove the camshaft mounting bracket bolts gradually in two or three stages. Remove the front oil seals, camshafts and hydraulic lifters. To disassemble the valve mechanism, special tool J-36420 and J-36467 or equivalents are needed.

INSPECTION



See Figures 5, 6 and 7



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Fig. Fig. 5: Measuring the valve stem diameter



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Fig. Fig. 6: Measuring the valve guide inside diameter using a dial indicator



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Fig. Fig. 7: The diameter, stem, face, face angle and tip must be checked before installing a valve

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

Thorough inspection of the valves requires the use of a micrometer and a dial indicator. If these instruments are not available, the parts should be taken to a reputable machine shop for inspection. Refer to the Valve Specifications chart, for the valve stem and stem-to-guide specifications.

Using a dial indicator, measure the inside diameter of the valve guides at their bottom, midpoint and top positions, at 90° apart. Subtract the valve stem measurement; if the clearance exceeds that listed in the specifications chart under Stem-to-Guide Clearance, replace the valve(s).

Check the top of each valve 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 0.02 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 ground, make sure that the valve is fixed securely into the jig, so that the tip contacts the grinding wheel squarely at exactly 90°. This procedure should be done by a machine shop with special grinding equippment.

REFACING



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.

Valve Lapping

See Figure 8



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Fig. Fig. 8: Hand lapping the valve to valve seat

All valve grinding operations should be performed by a qualified machine shop; only the valve lapping operation is recommended to be performed by the home mechanic. If new valves are going to be installed a machine shop should install them. The valve seat insert should be cut to match the new valve. Lapping new valves into old seats will not seat properly due to the new harder metals.

When valve faces and seats have been refaced, or if they are determined to be in good condition, the valves MUST BE lapped to ensure efficient sealing when the valve closes against the seat.

  1. Invert the cylinder head so that the combustion chambers are facing upward.
  2.  
  3. Lightly lubricate the valve stems with clean engine oil and coat the valve seats with valve lapping compound. Install the valves in the cylinder head as numbered.
  4.  
  5. Moisten and attach the suction cup of a valve lapping tool to a valve head.
  6.  
  7. Rotate the tool between your palms, changing position and lifting the tool often to prevent grooving. Lap the valve until a smooth polished seat is evident (you may have to add a bit more compound after some lapping is done).
  8.  
  9. Remove the valve and tool, then remove ALL traces of the grinding compound with a solvent-soaked rag or rinse the head with solvent.
  10.  

Valve lapping can also be done by fastening a suction cup to a piece of drill rod in a hand egg-beater type drill. Proceed as above, using the drill as a lapping tool. Due to the higher speeds involved when using the hand drill, care must be exercised to avoid grooving the seat. Lift the tool and change direction of rotation often.

 
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