GM Astro/Safari 1985-1996 Repair Guide

Valves

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REMOVAL & INSTALLATION



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



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Fig. Fig. 1: Compress the valve springs, then remove the valve keys in order to free the assembly ...



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Fig. Fig. 2: ... then remove the spring from the valve stem in order to access the seal



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Fig. Fig. 3: Remove the valve stem seal from the cylinder head



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Fig. Fig. 4: Invert the cylinder head and withdraw the valve from the cylinder head bore



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Fig. Fig. 5: A valve spring compressor is necessary to remove the valves-this C-clamp style model can only be used with the cylinder head removed from the engine. Jawed types, such as seen in the photos can also be used with the head installed



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Fig. Fig. 6: Exploded and cross-sectional view of a common valve component assembly-2.5L engine shown



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Fig. Fig. 7: Exploded view of early-model 4.3L engine valves and components-late-model similar

If the valve springs are suspect, you may wish to measure the installed height BEFORE removing them. For details, please refer to the valve spring inspection information, later in this section.

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. In some applications Teflon guide seals are available. Check with a machinist and/or automotive parts store for a suggestion on the proper seals to use.

  1. Remove the cylinder head(s), and place on a clean surface.
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  3. Using a suitable spring compressor (either a leverage or jawed type that is designed for pushrod overhead valve engines), compress the valve spring and remove the valve spring cap keys. Carefully 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 and the spring seat (if applicable) from the 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 with drilled holes or cardboard. Make sure you number each hole in the holder to keep the valves in proper order; they MUST be installed in their original locations. Another method of sorting the valve components is to use numbered containers, and make sure the components from each valve is stored in a separate container.
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  7. Use an electric drill and rotary wire brush to clean the intake and exhaust valve ports, combustion chamber and valve seats. In some cases, the carbon build-up will have to be chipped away. Use a blunt pointed drift for carbon chipping, being careful around valve seat areas.
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  9. Use a valve guide cleaning brush and suitable solvent to clean the valve guides.
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  11. Clean the valves with a revolving wire brush. Heavy carbon deposits may be removed with a blunt drift.
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When using a wire brush to remove carbon from the cylinder head or valves, make sure the deposits are actually removed and not just burnished.

  1. Wash and clean all valve springs, retainers etc., in safe solvent. Remember to keep parts from each valve separate.
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  3. Check the cylinder head for cracks. Cracks usually start around the exhaust valve seat because it is the hottest part of the combustion chamber. If a crack is suspected but cannot be detected visually, have the area checked by pressure testing, with a dye penetrant or other method by an automotive machine shop.
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  5. Inspect the valves, guides, springs and seats and machine or replace parts, as necessary.
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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 spring seats (if applicable), new seals and valve springs, again one valve at a time.
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  7. Install the spring caps, 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 needle-nose pliers (or your fingers), carefully 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 be raised as the compressor is released, retaining the key.
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  13. Install the cylinder head(s).
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INSPECTION



See Figures 8, 9, 10, 11, 12 and 13



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Fig. Fig. 8: Check the valve for damage or wear in these critical areas



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Fig. Fig. 9: A valve worn out of specification should be replaced



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Fig. Fig. 10: Valve stem wear patterns on engines equipped with rotator cups



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



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Fig. Fig. 12: Valve stems may be rolled on a flat surface to check for bends



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Fig. Fig. 13: Use a micrometer to check the valve stem diameter

Excessive valve stem-to-bore clearance will cause excessive oil consumption and may cause valve breakage. Insufficient clearance will result in noisy and sticky functioning of the valve and disturb engine smoothness.

Inspect the valve faces and seats (in the head) for pits, burned spots and other evidence of poor seating. Valves that are pitted must be refaced to the proper angle (45°). Valves that are warped excessively must be replaced. When a valve head that is warped excessively is refaced, a knife edge will be ground on part or all of the valve head due to the amount of material that must be removed to completely reface the valve. Knife edges lead to breakage, burning or preignition due to heat localizing on the knife edge. If the edge of the valve head is less than 1 / 32 in. (0.8mm) after machining, replace the valve. We recommend that all machine work be performed by a reputable machine shop.

Make sure the valve stem is not bent. The valve may be rolled on a flat surface such as a mirror or glass. An even better indication of valve stem bending can be determined by carefully chocking the stem into an electric drill. Use the drill the spin the stem while you watch the valve head. A bent stem will be obvious by the wobbling of the head. Be very careful if this method is used. If the valve stem is not properly chocked in position it could come flying out of the drill and cause injury.

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.

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. Check the valve stem-to-guide clearance in one or more of the following manners, but do not rely on the visual inspection alone:

  1. A visual inspection can give you a fairly good idea if the guide, valve stem or both are worn. Insert the valve into the guide until the valve head is slightly away from the valve seat. Wiggle the valve sideways. A small amount of wobble is normal, excessive wobble means a worn guide and/or valve stem.
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If a dial indicator and micrometer are not available to you, take your cylinder head and valves to a reputable machine shop of inspection.

  1. If a dial indicator is on hand, mount the indicator so that gauge stem is 90° to the valve stem as close to the top of the valve guide as possible. Move the valve from the seat, and measure the valve guide-to-stem clearance by rocking the stem back and forth to actuate the dial indicator. Measure the valve stem using a micrometer and compare to specifications to determine whether stem or guide is causing excessive clearance.
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  3. If both a ball gauge and a micrometer are available, first, measure the inside diameter of the valve guide bushing at three locations using the ball gauge. Second, use the micrometer to measure the stem diameter. Finally, subtract the valve stem diameter from the corresponding valve guide inside diameter to arrive at the valve clearance. If clearance is greater than specification, the valve and guide bushing must be replaced.
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The valve guide, if worn, must be repaired before the valve seats can be resurfaced. A new valve guide should be installed or, in some cases, knurled. Consult an automotive machine shop.

If the valve guide is okay, measure the valve seat concentricity using a runout gauge. Follow the manufacturers instructions. If runout is excessive, reface or replace the valve and machine or replace the valve seat.

Valves and seats must always be machined together. Never use a refaced valve on a valve seat that has not been machined; never use a valve that has not been refaced on a machined valve seat.

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. Refacing may be necessary in order to correct 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 14 and 15



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Fig. Fig. 14: Lapping the valves by hand



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Fig. Fig. 15: Homemade lapping tool

After machine work has been performed on the valves, it may be necessary to lap the valves 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. Keep in mind that 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 its sticking to the valve.
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  7. Rotate the tool between your 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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