GM Astro/Safari 1985-1996 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 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 by this guide utilize hydraulic valve lifters. The purpose of 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 which 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



2.5L Engine

See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: Valve arrangement-2.5L engines (E=Exhaust; I=Intake)

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 rockers arms have been disturbed for any reason such as cylinder head, camshaft, pushrod or lifter removal.

  1. Disconnect the negative battery cable for safety.
  2.  
  3. Remove the engine cover from the passenger compartment for access.
  4.  
  5. Remove the rocker arm cover. For details, please refer to Engine & Engine Rebuilding of this guide.
  6.  
  7. Rotate the crankshaft until the mark on the damper pulley aligns with the 0 mark on the timing plate and the No. 1 cylinder is on the compression stroke.
  8.  

To determine if the No. 1 cylinder is on the compression stroke, shake the rocker arms of the No. 1 cylinder, if they move the cylinder is on the compression stroke, if they don't move the cylinder is on the exhaust stroke. If the cylinder is on the exhaust stroke, it will be necessary to rotate the crankshaft 1 more full revolution to bring No. 1 back to top on compression.

  1. With the engine on the compression stroke, adjust the exhaust valves of cylinders No. 1 and 3 and the intake valves of cylinders No. 1 and 2.
  2.  
  3. To adjust the valves, tighten the rocker arm studs to the specified torque:

    1985-86: 20 ft. lbs. (28 Nm).
     
    1987: 24 ft. lbs. (32 Nm).
     
    1988-90: 22 ft. lbs. (30 Nm).
     

  4.  

  1. Rotate the crankshaft 1 complete revolution and align the mark on the damper pulley with the 0 mark on the timing plate.
  2.  
  3. With the engine on the No. 4 compression stroke, tighten the retainers for the exhaust valves of cylinders No. 2 and 4 and the intake valves of cylinders No. 3 and 4.
  4.  
  5. Install the rocker arm cover.
  6.  
  7. Connect the negative battery cable, then run the engine and verify there are no leaks.
  8.  
  9. Shut the engine OFF , then install the engine cover. You may wish to allow the engine to cool first as you may be working near HOT components.
  10.  

4.3L Engine
VIN Z

See Figures 2 and 3



Click image to see an enlarged view

Fig. Fig. 2: Valve arrangement-4.3L engines (E=Exhaust; I=Intake)



Click image to see an enlarged view

Fig. Fig. 3: Adjust the rockers, by rotating the pushrods between your thumb and forefinger to feel for play

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 rockers arms have been disturbed for any reason such as cylinder head, camshaft, pushrod or lifter removal.

For 1993-94, the 4.3L (VIN Z) engine may be equipped with either of 2 rocker arm retaining systems. If your engine utilizes screw-in type rocker arm studs with positive stop shoulders, no valve lash adjustment is necessary or possible. If equipped, please refer to the 4.3L (VIN W) valve lash information, found later in this section. If however, your engine utilizes the pressed-in rocker arm studs, use the following procedure to tighten the rocker arm nuts and properly center the pushrod on the hydraulic lifter:

  1. Disconnect the negative battery cable for safety.
  2.  
  3. Remove the engine cover from the passenger compartment for access.
  4.  
  5. Remove the rocker arm covers. For details, please refer to Engine & Engine Rebuilding of this guide.
  6.  
  7. To prepare the engine for valve adjustment, rotate the crankshaft until the mark on the damper pulley aligns with the 0° mark on the timing plate and the No. 1 cylinder is on the compression stroke. You will know when the No. 1 piston is on it's 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, 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 of the lash is removed.
    4.  
    5. When the play has disappeared, turn the adjusting nut inward 1 additional turn for 1988-93 engines or 1 3 / 4 additional turns for 1994 engines.
    6.  

  2.  
  3. Rotate the crankshaft 1 complete revolution and align the mark on the damper pulley with the 0° 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 of the lash is removed.
    4.  
    5. When the play has disappeared, turn the adjusting nut inward 1 additional turn for 1988-93 engines or 1 3 / 4 additional turns for 1994 engines.
    6.  

  4.  
  5. Install the rocker arm covers.
  6.  
  7. Connect the negative battery cable, then run the engine and verify there are not leaks.
  8.  
  9. Shut the engine OFF , then install the engine cover. You may wish to allow the engine to cool first as you may be working near HOT components.
  10.  

VIN W

See Figure 2

The 4.3L (VIN W) engine and some of the 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 torqued 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.

 
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