GM Full-Size Trucks 1988-1998 Repair Information

Valve Lash

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All engines described here use hydraulic lifters, which require no periodic adjustment. In the event of cylinder head removal or any operation that requires disturbing the rocker arms, the rocker arms will have to be adjusted.

ADJUSTMENT



4.8L Engines
  1. Remove the rocker arm cover.
  2.  
  3. Mark the distributor housing at the No. 1 and No. 6 wire positions and remove the cap.
  4.  
  5. Turn the crankshaft until the rotor points to the No. 1 position. The following valves can be adjusted:

    No. 1 exhaust and intake
     
    No. 2 intake
     
    No. 3 exhaust
     
    No. 4 intake
     
    No. 5 exhaust
     

  6.  

To adjust a valve, back off the adjusting nut until lash (play) is felt at the pushrod. Tighten the nut just until all lash is removed. This can be determined by rotating the pushrod with your fingers. When all lash is removed, the pushrod will stop rotating. When all play is removed, tighten the nut 1 full turn (360°).

  1. Rotate the crankshaft until the rotor points to the No. 6 position. The following valves can be adjusted:

    No. 2 exhaust
     
    No. 3 intake
     
    No. 4 exhaust
     
    No. 5 intake
     
    No. 6 intake and exhaust
     

  2.  

  1. Install the distributor cap.
  2.  
  3. Install the rocker cover.
  4.  

V6 and V8 Engines

See Figure 1

  1. Remove the rocker covers and gaskets.
  2.  
  3. Crank the engine until the mark on the damper aligns with the TDC or 0 mark on the timing tab and the engine is in No. 1 firing position. This can be determined by placing your finger on the No. 1 cylinder valves as the marks align. If the valves do not move, it is in No. 1 firing position. If the valves move, it is in No. 6 firing position (No. 4 on the V6) and the crankshaft should be rotated 1 more revolution to the No. 1 firing position. To adjust a valve, back off the adjusting nut until lash (play) is felt at the pushrod. Tighten the nut just until all lash is removed. This can be determined by rotating the pushrod with your fingers. When all lash is removed, the pushrod will stop rotating. When all play is removed, tighten the nut 1 full turn (360°).
  4.  



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Fig. Fig. 1: Adjusting the valve-gasoline engines

  1. With the engine in No. 1 firing position, the following valves can be adjusted:
  2.  

V6 Engines


Exhaust-1, 5, 6,
 
Intake-1, 2, 3,
 

V8 Engines


Exhaust-1,3,4,8
 
Intake-1,2,5,7
 

  1. Crank the engine 1 full revolution until the marks are again in alignment. This is No. 6 firing position (No. 4 on the V6). The following valves can now be adjusted:
  2.  

V6 Engines


Exhaust-2, 3, 4
 
Intake-4, 5, 6
 

V8 Engines


Exhaust-2,5,6,7
 
Intake-3,4,6,8
 

  1. Reinstall the rocker arm covers using new gaskets.
  2.  
  3. Install the distributor cap and wire assembly.
  4.  

 
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