GM Blazer/Jimmy/Typhoon/Bravada 1983-1993 Repair Guide

Valves

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REMOVAL & INSTALLATION



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

All O-rings removed from the valve stem should be discarded and replaced with new ones.

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.
  2.  
  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 keeper. Carefully release the spring compressor and remove the valve spring and cap (and valve rotator on some engines).
  4.  

Use care in removing the keepers; 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.
  2.  
  3. Slide the valves out of the head from the combustion chamber side.
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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 (if used) may be removed from the valve stem



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Fig. Fig. 5: After the seal and spring seat are removed, invert the cylinder head and withdraw the valve from the bore

  1. 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 are stored in a separate container.
  2.  
  3. 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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  5. Use a valve guide cleaning brush and suitable solvent to clean the valve guides.
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  7. 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.
  2.  
  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.
  4.  
  5. Inspect the valves, guides, springs and seats, then machine or replace parts, as necessary.
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To install:
  1. Lubricate the valve stems with clean engine oil.
  2.  
  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.
  6.  



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



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Fig. Fig. 7: Exploded view of the 4.3L engine valves and components

  1. Install the spring caps, and compress the springs.
  2.  
  3. With the valve keeper groove exposed above the compressed valve spring, wipe some wheel bearing grease around the groove. This will retain the keepers as you release the spring compressor.
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  5. Using needle nose pliers (or your fingers), carefully place the keepers in the grooves. The grease should hold the keepers in place. Slowly release the spring compressor; the valve cap or rotator will raise up as the compressor is released, retaining the keeper.
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  7. Install the cylinder head(s).
  8.  

INSPECTION



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

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. (1mm) 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 to 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.



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



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Fig. Fig. 9: Use a micrometer to measure the valve stem diameter



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Fig. Fig. 10: Valve stems may be rolled on a flat surface to check for bends

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.
  4.  

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 the 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.



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Fig. Fig. 11: Valve inspection and measurement



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Fig. Fig. 12: Valve stem wear patterns on engines equipped with rotator cups



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Fig. Fig. 13: A run-out (dial) gauge is used to check valve seat concentricity

VALVE REFACING



All valve grinding operations should be performed by a qualified machine shop; only the valve lapping operation is recommended to be performed by the home mechanic.

Valve Lapping

See Figure 14

When valve faces and seats have been refaced, or if they are determined to be in good condition, the valves may have to be lapped to ensure efficient sealing when the valve closes against the seat. But, modern metals used in valves/seats and the extremely accurate machining available today may preclude the need to lap. Consult your machinist to determine if lapping is necessary. If so, proceed as follows:

  1. Invert the cylinder head so that the combustion chambers are facing upward.
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  3. Lightly lubricate the valve stems with clean engine oil and coat the valve seats with valve lapping compound. Install the valves in the cylinder head as numbered.
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  5. Moisten and attach the suction cup of a valve lapping tool to a valve head.
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  7. Rotate the tool between your 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).
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  9. Remove the valve and tool, then remove ALL traces of the grinding compound with a solvent-soaked rag or rinse the head with solvent.
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Valve lapping can also be done by fastening a suction cup to a piece of drill rod in a hand egg-beater 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. 14: Lapping the valves by hand

 
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