GM Prizm/Nova 1985-1993 Repair Guide

ADJUSTMENT

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1985-88 VIN Code 4 Carbureted Engine

See Figures 1, 2 and 3

  1. Start the engine and run it until it reaches normal operating temperature.
  2.  
  3. Stop the engine. Remove the air cleaner assembly. Remove the valve cover.
  4.  


CAUTION
Be careful when removing components; the engine will be hot.

  1. Turn the crankshaft until the pointer or notch on the pulley aligns with the O or the T mark on the timing scale. This will ensure that the engine is at TDC. Turning the engine (with a wrench on the crankshaft bolt) is much easier if the spark plugs are removed.
  2.  

Check that the rocker arms on the No. 1 cylinder are loose and those on the No. 4 cylinder are tight. If not, turn the crankshaft one complete revolution (360°).

  1. Using a feeler gauge, check the clearance between the bottom of the rocker arm and the top of the valve stem. This measurement should correspond to the one given in the Tune-Up Specifications Chart in this section. Check only the valves listed under First in the accompanying illustrations for your engine.
  2.  



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Fig. Fig. 1: Adjust these valves first on the 1985-88 VIN Code 4 carbureted engines



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Fig. Fig. 2: Adjust these valves second on the 1985-88 VIN Code 4 carbureted engines



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Fig. Fig. 3: Checking the valve lash

  1. If the clearance is not within specifications, the valves will require adjustment. Loosen the locknut on the rocker arm and, still holding the nut with an open end wrench, turn the adjustment screw to achieve the correct clearance. This is a detail-oriented job; work for exact clearance.
  2.  
  3. Once the correct clearance is achieved, keep the adjustment screw from turning with your screwdriver, and then tighten the locknut. Recheck the valve clearance. If it's proper, proceed to the next valve as shown on the diagram.
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  5. After the correct four valves have been adjusted, turn the engine one complete revolution (360°) and adjust the remaining valves. Follow steps 4-6 and use the valve arrangement illustration marked Second.
  6.  
  7. Use a new gasket and then install the valve cover. Install any other components which were removed for access to the cover.
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  9. Start the engine. Listen for any excessive tapping (indicating a loosened rocker) and check the valve cover for any signs of oil leaks.
  10.  

1988 VIN Code 5 Fuel Injected Engine All 1989-93 Engines

See Figures 4 through 11


WARNING
The use of the correct special tools or their equivalent is REQUIRED for this procedure. The valve adjustment requires removal of the adjusting shims (Tool kit J-37141 or equivalent) and accurate measurement of the shims with a micrometer. A selection of replacement shims is also required. Do not attempt this procedure if you are not equipped with the proper tools.



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Fig. Fig. 4: First pass when checking valve clearance on the 1988-93 fuel injected engines



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Fig. Fig. 5: Second pass when checking valve clearance on the 1988-93 fuel injected engines



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Fig. Fig. 6: Use the correct tools to depress and hold down the valve lifter



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Fig. Fig. 7: Carefully remove the shim to be replaced (above) with a small screwdriver and magnetic tools. Clean and dry the shim before measuring with the micrometer (below)

Valves on this motor are adjusted with the engine cold. Do not attempt adjustment if the engine has been run within the previous 4 hours. An overnight cooling period is recommended.

  1. Remove the valve cover following procedures discussed in Engine & Engine Rebuilding .
  2.  
  3. Turn the crankshaft to align the groove in the crankshaft pulley with the 0 mark on the timing belt cover. Removing the spark plugs makes this easier, but is not required.
  4.  
  5. Check that the lifters on No. 1 cylinder are loose and those on No. 4 are tight. If not, turn the crankshaft pulley one full revolution (360°).
  6.  
  7. Using the feeler gauge, measure the clearance on the four valves shown in the diagram labeled First Pass. Make a WRITTEN record of any measurements which are not within specification.
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  9. Rotate the crankshaft pulley one full turn (360°) and check the clearance on the other four valves. These are shown on the diagram labeled Second Pass. Any measurements not within specification should be added to your WRITTEN record.
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  11. For ANY given valve needing adjustment:
    1. Turn the crankshaft pulley until the camshaft lobe points upward over the valve. This takes the tension off the valve and spring.
    2.  
    3. Using the forked tool, press the valve lifter downward and hold it there. Some tool kits require a second tool for holding the lifter in place, allowing the first to be removed.
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    5. Using small magnetic tools, remove the adjusting shim from the top of the lifter.
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    7. Use the micrometer and measure the thickness of the shim removed. Determine the thickness of the new shim using the formula below or the selection charts. For the purposes of the following formula, T = Thickness of the old shim; A = Valve clearance measured; N = Thickness of the new shim.

      For the intake side (camshaft nearest to the intake manifold):N = T + (A - 0.20mm or 0.008 in.)
       
      For the exhaust side (camshaft nearest to the exhaust manifold):N = T + (A - 0.25mm or 0.010 in.)
       

    8.  
    9. Select a shim closest to the calculated thickness. Use the lifter depressor tool to press down the lifter and install the shim. Shims are available in 17 sizes from 2.50mm (0.0984 in.) to 3.30mm (0.1299 in.). The standard increment is 0.05mm (0.002 in.)
    10.  
    11. Repeat Steps a through e for each valve needing adjustment.
    12.  

  12.  
  13. Reinstall the valve cover, following the procedures outlined in Engine & Engine Rebuilding .
  14.  
  15. Check and adjust the timing and idle speed, following the procedures outlined in this section.
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Fig. Fig. 8: Exhaust valve adjusting shim selection chart - 1988-92



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Fig. Fig. 9: Intake valve adjusting shim selection chart - 1988-92



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Fig. Fig. 10: Intake valve adjusting shim selection chart - 1993



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Fig. Fig. 11: Exhaust valve adjusting shim selection chart - 1993

 
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