GM Full Size Vans 1967-1986 Repair Guide

Valves

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REMOVAL & INSTALLATION



See Figures 1 through 7

  1. Remove the head(s), 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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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 magnet may be helpful in removing the valve keepers

  1. Slide the valves out of the head from the combustion chamber side.
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  3. Make a holder for the valves out of a piece of wood or cardboard. 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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New valve seals must be installed when the valve train is put back together. Certain seals slip over the valve stem and guide boss, while others require that the boss be machined. Teflon® guide seals are available. Check with a machinist and/or automotive parts store for a suggestion on the proper seals to use.

Remember that when installing valve seals, a small amount of oil must be able to pass the seal to lubricate the valve guides; otherwise, excessive wear will result.



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Fig. Fig. 3: Be careful not to lose 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: Remove the valve stem seal from the cylinder head



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Fig. Fig. 7: Invert the cylinder head and withdraw the valve from the cylinder head bore

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 needlenose 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).
  14.  

INSPECTION



See Figures 8 through 12



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Fig. Fig. 8: Common valve dimensions



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Fig. Fig. 9: Multiple views of common valve stem wear

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°. 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 an 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° 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.



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Fig. Fig. 10: A dial gauge may be used to check valve stem-to-guide clearance



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Fig. Fig. 11: Valve stems may be rolled on a flat surface to check for bends

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. 12: Use a micrometer to check the valve stem diameter

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 Figures 13 and 14



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Fig. Fig. 13: Lapping the valves by hand



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Fig. Fig. 14: A homemade valve lapping tool

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 sure the valve faces, seats, cylinder ports and valve guides are clean before reassembling the valve train.
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