GM Full-Size Trucks 1970-1979 Repair Guide

Valves

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REMOVAL & INSTALLATION



Cylinder Heads Removed

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



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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: A small magnet will help in removal of the valve keepers



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Fig. Fig. 3: Be careful not to lose the valve keepers



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Fig. Fig. 4: Once the spring has been removed, the O-ring may be removed from the valve stem



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Fig. Fig. 5: With the valve spring out of the way, the valve stem seals may now be replaced



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Fig. Fig. 6: Invert the cylinder head and withdraw the valve from the cylinder head bore



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Fig. Fig. 7: A wire wheel may be used to clean the combustion chambers of carbon deposits



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Fig. Fig. 8: A dial gauge may be used to check valve stem-to-guide clearance

  1. Remove the cylinder head(s) from the vehicle, and place on a clean surface.
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  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).
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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.
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  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 pushrods in gasoline engine 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.
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To install:
  1. Lubricate the valve stems with clean engine oil.
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  3. Install the valves in the cylinder head, one at a time, as numbered.
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  5. Lubricate and position the seals and valve springs, again a valve at a time.
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  7. Install the spring retainers, and compress the springs.
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  9. With the valve key groove exposed above the compressed valve spring, wipe some wheel bearing grease around the groove. This will retain the keys as you release the spring compressor.
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  11. Using needlenosed pliers (or your fingers), place the keys in the key grooves. The grease should hold the keys in place. Slowly release the spring compressor; the valve cap or rotator will raise up as the compressor is released, retaining the keys.
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  13. Install the rocker assembly, and install the cylinder head(s).
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Cylinder Head(s) Installed

It is often not necessary to remove the cylinder head(s) in order to service the valve train. Such is the case when valve seals need to be replaced. Valve seals can be easily replaced with the head(s) on the engine; the only special equipment needed for this job are an air line adapter (sold in most auto parts stores), which screws a compressed air line into the spark plug hole of the cylinder on which you are working, and a valve spring compressor. A source of compressed air is needed, of course.

  1. Remove the valve cover as previously detailed.
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  3. Remove the spark plug, rocker arm and push rod on the cylinder(s) to be serviced.
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  5. Install the air line adapter (GM tool #J-23590 or equivalent) into the spark plug hole. Turn on the air compressor to apply compressed air into the cylinder. This keeps the valves up in place.
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Set the regulator of the air compressor at least 50 pounds to ensure adequate pressure.

  1. Using the valve spring compressor, compress the valve spring and remove the valve keys and keepers, the valve spring and damper.
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  3. Remove the valve stem seal.
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To install:
  1. Oil the valve stem and new seal. Install a new seal over the valve stem.
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  3. Set the spring, damper and keeper in place.
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  5. Compress the spring. Coat the keys with grease to hold them onto the valve stem and install the keys, making sure they are seated fully in the keeper.
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  7. Remove the air line adapter and install the spark plugs.
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  9. Install the pushrods and rocker arms.
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  11. Reinstall the valve cover after adjusting the valves, as outlined in this section.
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INSPECTION



See Figures 9 and 10



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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

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 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 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 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.

LAPPING THE VALVES



See Figure 11



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Fig. Fig. 11: Lapping the valves by hand

After machine work has been performed on the valves, it may be necessary to lap the valve to assure proper contact. For this, you should first contact your machine shop to determine if lapping is necessary. Some machine shops will perform this for you as part of the service, but the precision machining which is available today often makes lapping unnecessary. Additionally, the hardened valves/seats used in modern automobiles may make lapping difficult or impossible. If your machine shop recommends that you lap the valves, proceed as follows:

  1. 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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  3. Lightly lube 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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  5. 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 it sticking to the valve.
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  7. Rotate the tool between the palms, changing position and lifting the tool often to prevent grooving. Lap the valve in until a smooth, evenly polished seat and valve face are evident.
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  9. 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.
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  11. Proceed through the remaining valves, one at a time. Make