GM Cadillac 1967-1989 Repair Guide

Valves and Springs

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REMOVAL & INSTALLATION



See Figures 1, 2, 3, 4, 5, 6, 7 and 8

  1. Remove the head(s), 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 and 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 guides. 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.
  4.  
  5. Make a holder for the valves out of a piece of wood or cardboard, as outlined for the pushrods in Cylinder Head Removal. Make sure you number each hole in the cardboard to keep the valves in proper order. Slide the valves out of the head from the combustion chamber side; they MUST be installed as they were removed.
  6.  



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Fig. Fig. 1: Valve train exploded view, all engines similar, except 8-429 and 6-252 engines (with rocker shafts)



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Fig. Fig. 2: Removing the valve springs



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Fig. Fig. 3: Compressing the valve spring with tool



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Fig. Fig. 4: Removing the valve keys



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Fig. Fig. 5: Removing the valve rotator



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Fig. Fig. 6: Removing the valve spring



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Fig. Fig. 7: Removing the valve



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Fig. Fig. 8: Removing the valve seal

INSPECTION



See Figures 9 through 15

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 re-facing 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 guides 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 the 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 for 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 wear 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.



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Fig. Fig. 9: Critical valve dimensions



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Fig. Fig. 10: Checking the valve stem-to-guide clearance



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Fig. Fig. 11: Valve stem wear



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Fig. Fig. 12: Have the valve seat concentricity checked at a machine shop



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



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Fig. Fig. 14: use a micrometer to measure the valve stem diameter



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Fig. Fig. 15: Valve stems may be rolled on a flat surface to check for bends

LAPPING THE VALVES



See Figures 16 and 17

When valve faces and seats have been re-faced and re-cut, or if they are determined to be in good condition, the valves must be lapped in to ensure efficient sealing when the valve closes against the seat.

  1. Invert the cylinder head so that the combustion chambers are facing up.
  2.  
  3. Lightly lubricate the valve stems with clean oil, and coat the valve seats with valve grinding compound. Install the valves in the head as numbered.
  4.  
  5. Attach the suction cup of a valve lapping tool to a valve head. You'll probably have to moisten the cup to securely attach the tool to the valve.
  6.  
  7. Rotate the tool between the 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, and remove ALL traces of grinding compound with 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 eggbeater 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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Fig. Fig. 16: Lapping the valves by hand



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Fig. Fig. 17: Hand-made valve lapping tool

 
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