GM Full Size Vans 1987-1997 Repair Guide

Valve Lash

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Valve lash adjustment determines how far the valves enter the cylinder and how long they stay open and/or closed.

While all the valve adjustments must be made as accurately as possible, it is better to have the valve adjustment slightly loose than slightly tight, as a burned valve may result from overly tight adjustments.

All of the engines covered in this guide utilize hydraulic lifters. The purpose of the hydraulic lifters is to automatically maintain zero valve lash, therefore no periodic adjustments are required on engines equipped with them. However, many of the vehicles utilize rocker arms that are retained by adjusting nuts. If the rocker arms and nuts are loosened or removed, they must be properly adjusted upon installation in order for the lifters to work.

ADJUSTMENT



4.3L Engine
VIN Z

See Figures 1 and 2

This engine utilizes hydraulic valve lifters which means that a valve adjustment is NOT a regular maintenance item. The valves must only be adjusted if the rocker arms have been disturbed for any reason such as cylinder head, camshaft, pushrod or lifter removal.

Some models utilize a screw in type rocker arm studs with positive stop shoulders, no adjustment is necessary or possible.

Other models utilize pressed-in rocker arm studs, use the following procedure to tighten the rocker arms nuts and properly center the pushrod on the hydraulic lifter:

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the engine cover.
  4.  
  5. Remove the rocker arm covers.
  6.  



Click image to see an enlarged view

Fig. Fig. 1: Valve arrangement - 4.3L engine (E=exhaust; I=intake



Click image to see an enlarged view

Fig. Fig. 2: Adjust the rockers, by rotating the pushrods between your thumb and forefinger to feel for play

  1. To prepare the engine for valve adjustment, rotate the crankshaft until the mark on the damper pulley aligns with the 0 degree mark on the timing plate and the No. 1 piston is on its compression stroke. You will know the No. 1 piston is on its compression stroke because both the intake and exhaust valves will remain closed as the crankshaft damper mark approaches the timing scale.
  2.  

Another method to tell when the piston is coming up on the compression stroke is by removing the spark plug and placing your thumb over the hole; you will feel the air being forced out of the spark plug hole. Stop turning the crankshaft when the TDC timing mark on the crankshaft pulley is directly aligned with the timing mark pointer or the zero mark on the scale.

  1. With the engine on the compression stroke, adjust the exhaust valves of cylinders No. 1, 5 and 6 and the intake valves of cylinders No. 1, 2 and 3 by performing the following procedures:
    1. Back out the adjusting nut until lash can be felt at the pushrod.
    2.  
    3. While rotating the pushrod, turn the adjusting nut inward until all the lash is removed.
    4.  
    5. When the play has disappeared, turn the adjusting nut inward 1 additional turn for 1987-93 engines and 1 3 / 4 turns for 1994 engines.
    6.  

  2.  
  3. Rotate the crankshaft 1 complete revolution and align the mark on the damper pulley with the 0 degree mark on the timing plate; the engine is now positioned on the No. 4 firing position. This time the No. 4 cylinder valves remain closed as the timing mark approaches the scale. Adjust the exhaust valves of cylinders No. 2, 3 and 4 and the intake valves of cylinders No. 4, 5 and 6 by performing the following procedures:
    1. Back out the adjusting nut until lash can be felt at the pushrod.
    2.  
    3. While rotating the pushrod, turn the adjusting nut inward until all the lash is removed.
    4.  
    5. When the play has disappeared, turn the adjusting nut inward 1 additional turn for 1987-93 engines and 1 3 / 4 turns for 1994 engines.
    6.  

  4.  
  5. Install the rocker arm covers.
  6.  
  7. Connect the negative battery cable, and verify that there are no leaks.
  8.  
  9. Turn the engine OFF , then install the engine cover. You may wish to allow the engine to cool first, as you will be working near hot components.
  10.  

VIN W

The 4.3L (VIN W) and some 4.3L (VIN Z) engines are equipped with screw-in type rocker arm studs with positive stop shoulders. Because the shoulders allow the rocker arms to be tightened into proper position, no adjustments are necessary or possible. If a valve train problem is suspected, check that the rocker arm nuts are tightened to 20 ft. lbs. (27 Nm). When valve lash falls out of specification (valve tap is heard), replace the rocker arm, pushrod and hydraulic lifter on the offending cylinder.

5.0L and 5.7L Engines

This engine utilizes hydraulic valve lifters, which means that valve adjustment is NOT a regular maintenance item. The valves must only be adjusted if the rocker arms have been disturbed for any reason such as cylinder head, camshaft, pushrod or lifter removal.

Some models utilize screw-in type rocker arm studs with positive stop shoulders, for which no adjustment is necessary or possible.

Other models utilize pressed-in rocker arm studs; for these models, use the following procedure to tighten the rocker arms nuts and properly center the pushrod on the hydraulic lifter:

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the engine cover.
  4.  
  5. Remove the rocker arm covers.
  6.  
  7. To prepare the engine for valve adjustment, rotate the crankshaft until the mark on the damper pulley aligns with the 0 degree mark on the timing plate and the No. 1 piston is on its compression stroke. You will know the No. 1 piston is on its compression stroke because both the intake and exhaust valves will remain closed as the crankshaft damper mark approaches the timing scale.
  8.  

Another method to tell when the piston is coming up on the compression stroke is by removing the spark plug and placing your thumb over the hole; you will feel the air being forced out of the spark plug hole. Stop turning the crankshaft when the TDC timing mark on the crankshaft pulley is directly aligned with the timing mark pointer or the zero mark on the scale.

  1. With the engine on the compression stroke, adjust the exhaust valves of cylinders No. 1, 3, 4 and 8 and the intake valves of cylinders No. 1, 2, 5 and 7 by performing the following procedures:
    1. Back out the adjusting nut until lash can be felt at the pushrod.
    2.  
    3. While rotating the pushrod, turn the adjusting nut inward until all the lash is removed.
    4.  
    5. When the play has disappeared, turn the adjusting nut inward 1 additional turn.
    6.  

  2.  
  3. Rotate the crankshaft 1 complete revolution and align the mark on the damper pulley with the 0 degree mark on the timing plate; the engine is now positioned on the No. 6 firing position. This time the No. 6 cylinder valves remain closed as the timing mark approaches the scale. Adjust the exhaust valves of cylinder No. 2, 5, 6 and 7 and the intake valves of cylinders No. 3, 4, 6 and 8 by performing the following procedures:
    1. Back out the adjusting nut until lash can be felt at the pushrod.
    2.  
    3. While rotating the pushrod, turn the adjusting nut inward until all the lash is removed.
    4.  
    5. When the play has disappeared, turn the adjusting nut inward 1 additional turn.
    6.  

  4.  
  5. Install the rocker arm covers.
  6.  
  7. Connect the negative battery cable, and verify that there are no leaks.
  8.  
  9. Turn the engine OFF , then install the engine cover. You may wish to allow the engine to cool first, as you will be working near hot components.
  10.  

 
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