Chevrolet Full-size Cars 1968-1978 Repair Guide

Valves and Springs

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REMOVAL & INSTALLATION





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Fig. Fig. 1 Use a valve spring compressor tool to relieve spring tension from the valve caps



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Fig. Fig. 2 Be careful not to lose the valve keepers



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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 Invert the cylinder head and withdraw the valve from the cylinder head bore

  1. Remove the heads, and place on a clean surface.
  2.  
  3. Using a suitable spring compressor (for pushrod-type overhead valve engines), compress the valve spring and remove the valve spring cap key. Release the spring compressor and remove the valve spring cap (and valve rotator on some engines).
  4.  

Use care in removing the keys; they are easily lost.

  1. Remove the valve seals from the intake valve guide. Throw these old seals away, as you'll be installing new seals during reassembly.
  2.  
  3. Slide the valves out of the head from the combustion chamber side.
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  5. Make a holder for the valves out of a piece of wood or cardboard, as outlined for the pushrod in Cylinder Head Removal. Make sure you number each hole in the cardboard to keep the valves in proper order. Slide the valve out of the head from the combustion chamber side; they MUST be installed as they were removed.
  6.  

INSPECTION





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Fig. Fig. 7 Critical valve dimensions and their measuring points



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Fig. Fig. 8 Examples of various valve tip wear patterns

Inspect the valve faces and seats (in the head) for pits, burned spots and other evidence of poor seating. If a valve face is in such bad shape that the head of the valve must be ground in order to true up the face, discard the valve because the sharp edge will run too hot. The correct angle for valve faces is 45 degrees. We recommend the refacing be done at a reputable machine shop.

Check the valve stem for scoring and burned spots. If not noticeably scored or damaged, clean the valve stem with solvent to remove all gum and varnish. Clean the valve guide using solvent and an expanding wire type valve guide cleaner. If you have access to a dial indicator for measuring valve stem-to-guide clearance, mount it so that the stem of the indicator is at 90 degrees to the valve stem, and as close to the valve guide as possible. 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 the excess clearance. If a dial indicator and micrometer are not available to you, take your cylinder head and valves to a reputable machine shop of inspection.

Some of the engines covered in this guide are equipped with valve rotators, which double as valve spring caps. In normal operation the rotators put a certain degree of wear on the tip of the valve stem; this ear appears as concentric rings on the stem tip. However, if the rotator is not working properly, the wear may appear as straight notches or X patterns across the valve stem tip. Whenever the valves are removed from the cylinder head, the tips should be inspected for improper pattern, which could indicate valve rotator problems. Valve stem tips will have to be ground flat if rotator patterns are severe.

REFACING





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Fig. Fig. 9 Valve stems may be rolled on a flat surface to check for bends



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Fig. Fig. 10 Use a micrometer to check the valve stem diameter



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Fig. Fig. 11 A dial gauge may be used to check valve stem-to-guide clearance

This procedure should only be performed by a qualified machine shop.

 
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