GM Metro/Sprint 1985-1993 Repair Guide

Valves

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REMOVAL and INSTALLATION

See Figures 1, 2 and 3



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Fig. Fig. 1: Camshaft and rocker arm assembly - Sprint



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Fig. Fig. 2: Camshaft and rocker arm assembly - Metro



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Fig. Fig. 3: Valve spring compressor

  1. Remove the cylinder head from the engine.
  2.  
  3. Remove the camshaft and, as required, the rocker arm assemblies.
  4.  
  5. On engines equipped with hydraulic lash adjusters, remove the adjusters and place in order of removal.
  6.  
  7. Using a spring compressor, compress the valve springs and remove the locks from the retainers.
  8.  
  9. Remove the retainers and springs from the cylinder head.
  10.  
  11. Remove the valve from the combustion chamber side of the cylinder head.
  12.  
  13. Remove the valve seal from the cylinder head.
  14.  

To install:
  1. Lubricate the valve with engine oil and install from the combustion chamber side of the cylinder head.
  2.  
  3. Install a new valve seal on the cylinder head.
  4.  
  5. Install the springs and retainers on the cylinder head one cylinder at a time.
  6.  
  7. Using a spring compressor, compress the valve springs and install the locks in the retainers.
  8.  
  9. Once all cylinders are assembled, use a rubber hammer to hit each valve assembly on the retainer side. This will positively seat the locks in the retainer.
  10.  
  11. On engines equipped with hydraulic lash adjusters, lubricate and install the adjusters in their original positions.
  12.  
  13. Install the camshaft and, as required, the rocker arm assemblies.
  14.  
  15. Install the cylinder head on the engine.
  16.  
  17. Adjust valve lash as required.
  18.  

INSPECTION



See Figures 4, 5, 6 and 7



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Fig. Fig. 4: Measuring valve head thickness



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Fig. Fig. 5: Inspecting valve head



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Fig. Fig. 6: Measuring valve radial runout



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Fig. Fig. 7: Measuring valve stem end deflection

  1. Check each valve for wear, burn or distortion at its face and stem and replace as necessary.
  2.  
  3. Check each valve stem end face for pitting and wear. If found, valve stem end may be resurfaced. Replace valve if chamfer area is excessively worn.
  4.  
  5. Measure the thickness of the valve head using a steel scale. Thickness should be a minimum of 0.023 in. (0.6mm) on the intake and 0.027 in. (0.7mm) on the exhaust.
  6.  
  7. Measure the valve for radial runout using a V-block and a dial indicator. If runout exceeds 0.003 in. (0.08mm), replace the valve.
  8.  
  9. Check the valve-to-valve guide clearance. Assemble a dial indicator on the cylinder head at a 45° angle to the valve stem end. Move the valve off the seat and then from side to side against the dial indicator. If valve stem end deflection is greater than 0.005 in. (0.14mm) for the intake valve, or 0.007 in. (0.18mm) for the exhaust valve, replace the valve and valve guide.
  10.  

RESURFACING



See Figures 8 and 9

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.

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.



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Fig. Fig. 8: Measuring valve seat contact width



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Fig. Fig. 9: Hand lapping the valves

  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.  
  11. The pattern produced on the seating face of each valve must be a continuous ring without any break and at a width of 0.512-0.590 in. (1.3-1.5mm) for both intake and exhaust valves.
  12.