GM Caprice 1990-1993 Repair Guide

Valve Lash

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All models utilize a hydraulic valve lifter system to obtain zero lash. No adjustment is necessary. An initial adjustment is required anytime that the lifters are removed or the valve train is disturbed.

ADJUSTMENT



EXCEPT 5.0L (VIN Y) ENGINE

See Figure 1

The valves may be adjusted with the engine idling or shut off. If you choose to adjust the valves with the engine idling, the use of oil stopper clips, which prevent oil splatter is recommended and the valves may be adjusted in any sequence.

If you adjust the valves with the engine shut off it will be a much cleaner process, but you will need to follow a cylinder and valve adjustment procedure.

To adjust the valves with the engine running proceed as follows:

Establish normal operating temperature by running the engine for several minutes. Shut the engine off and remove the valve cover(s). After valve cover removal, torque the cylinder heads to specification. Plug all open vacuum lines.

Restart the engine. Valve lash is set with the engine warm and idling. Turn the rocker arm nut counterclockwise until the rocker arm begins to clatter. Reverse the direction and turn the rocker arm down slowly until the clatter just stops. This is the zero lash position. Turn the nut down an additional 1 / 4 turn and wait ten seconds until the engine runs smoothly. Continue with additional 1 / 4 turns, waiting ten seconds each time, until the nut has been turned down one full turn from the zero lash position. This one turn, pre-load adjustment must be performed to allow the lifter to adjust itself and prevents possible interference between the valves and pistons. Noisy lifters should be cleaned or replaced.

To adjust the valves with the engine OFF

proceed as follows:
  1. Adjust the valves as follows:
    1. 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 the fingers 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. 4 (V6) or No. 6 (V8) firing position and the crankshaft should be rotated one more revolution to the No. 1 firing position.
    2.  
    3. The adjustment is made in the same manner on both engines.
    4.  
    5. With the engine in 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
       

    6.  

  2.  


NOTE
Distinguishing the exhaust from intake valves is easy, simply look for the intake or exhaust runner directly in-line with the valve.



Click image to see an enlarged view

Fig. Fig. 1: Valve adjustment - V8 engine

  1. Back the adjusting nut out until lash can be felt at the push rod, then turn the nut until all lash is removed (this can be determined by rotating the push rod while turning the adjusting nut). When all lash has been removed, turn the nut in 1 additional turn, this will center the lifter plunger.
  2.  
  3. Crank the engine 1 full revolution until the marks are again in alignment. This is No. 4 (V6) or No. 6 (V8) firing position. 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
     

  4.  


NOTE
Distinguishing the exhaust from intake valves is easy, simply look for the intake or exhaust runner directly in-line with the valve.

  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.  

5.0L (VIN Y) ENGINE

The 5.0L (VIN Y) engine uses a positive stop type rocker bolt; the lifters are automatically adjusted and centered when the rocker bolts are properly torqued down to 22 ft. lbs. (28 Nm). If a lifter is still noisy; refer to Engine & Engine Rebuilding - Camshaft Inspection.

 
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