GM Full-Size Trucks 1980-1987 Repair Guide

Valve Lash Adjustment

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See Figures 1, 2, 3, 4 and 5

The valve lash adjustment procedure is for hydraulic lifters which are filled with oil either from previous use (old lifters on which the oil has not drained) or from priming before installation (new lifters or old lifters on which oil had drained while removed from the engine).

All engines described in this information 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.

  1. Remove the rocker covers and gaskets.
  2.  



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Fig. Fig. 1: Chevrolet Intake (I) and Exhaust (E) valve arrangements (except V6 engine)



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Fig. Fig. 2: V6 262 valve arrangement (E- Exhaust; I- Intake)

  1. Adjust the valves on in-line 6 cylinder engines as follows:
    1. Mark the distributor housing with a piece of chalk at the No. 1 and 6 plug wire positions. Remove the distributor cap with the plug wires attached.
    2.  
    3. Crank the engine until the distributor rotor points to the NO. 1 cylinder and the No. 1 piston is at TDC (both No. 1 cylinder valves closed). At this point, adjust the following valves:

      No. 1 Exhaust and Intake
       
      No. 2 Intake
       
      No. 3 Exhaust
       
      No. 4 Intake
       
      No. 5 Exhaust
       

    4.  
    5. Back out the adjusting nut until lash is felt at the pushrod, then turn the adjusting nut in until all lash is removed. This can be determined by checking pushrod end-play while turning the adjusting nut. When all play has been removed, turn the adjusting nut in 1 full turn.
    6.  
    7. Crank the engine until the distributor rotor points to the No. 6 cylinder and the No. 6 piston is at TDC (both No. 6 cylinder valves closed). The following valves can be adjusted:

      No. 2 Exhaust
       
      No. 3 Intake
       
      No. 4 Exhaust
       
      No. 5 Intake
       
      No. 6 Intake and Exhaust
       

    8.  

  2.  



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Fig. Fig. 3: Valve adjustment, all except 6.2L diesel

  1. Adjust the valves on V8 and V6 engines as follows:
    1. Crank the engine until the mark on the damper aligns with the TDC or 0 degree mark on the timing tab and the engine is in the No. 1 firing position. This can be determined by placing your fingers on the No. 1 cylinder valves as the marks align. If the valves do not move, it is in the No. 1 firing position. If the valves move, it is in the No. 6 firing position (No. 4 on V6) and the crankcase should be rotated one more revolution to the No. 1 firing position.
    2.  
    3. With the engine in the No. 1 firing position, the following valves can be adjusted:

      V8: Exhaust 1, 3, 4, 8
       
      V8: Intake 1, 2, 5, 7
       
      V6: Exhaust 1, 5, 6
       
      V6: Intake 1, 2, 3
       

    4.  
    5. Back out the adjusting nut until lash is felt at the pushrod, then turn the adjusting nut in until all lash is removed. This can be determined by checking pushrod end-play while turning the adjusting nut. When all play has been removed, turn the adjusting nut in:

      1 /2-1 1 /4 additional turn (flat lifter)
       
      3 /4-1 1 /4 additional turn (roller lifter V8)
       
      3 /4 additional turn (roller lifter V6)
       

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

      V8: Exhaust 2, 5, 6, 7
       
      V8: Intake 3, 4, 6, 8
       
      V6: Exhaust 2, 3, 4
       
      V6: Intake 4, 5, 6
       

    8.  

  2.  



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Fig. Fig. 4: Diesel 350 V8 valve location



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Fig. Fig. 5: 6.2L (379) diesel engine valve arrangement

  1. Reinstall the rocker arm covers using new gaskets or sealer.
  2.  
  3. Install the distributor cap and wire assembly.
  4.  
  5. Adjust the carburetor idle speed.
  6.  

 
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