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Valve Clearance

CAUTION: Valve clearance should be checked with engine cold.
  1. Disconnect negative battery cable. Remove valve cover and gaskets. Rotate crankshaft until No. 1 cylinder is at TDC of compression stroke. Ensure timing mark on crankshaft pulley aligns with zero mark on timing belt cover.
  2. Valves on No. 1 cylinder should have clearance and be closed. If valves on No. 1 cylinder are not closed, rotate crankshaft one revolution (360 degrees).
  3. Using feeler gauge, measure and record clearance between camshaft lobe and adjuster shim on intake valves on cylinders No. 1 and 2 and exhaust valves on cylinders No. 1 and 3. Adjust valve clearance if it is not within specification. See VALVE CLEARANCE SPECIFICATIONS table.
    VALVE CLEARANCE SPECIFICATIONS

    Application In. (mm)
    Prizm & Prizm GSi
    Exhaust (1) .008-.012 (.20-.30)
    Intake (1) .006-.010 (.15-.25)
    (1) Adjustments made with engine cold.
  4. Rotate crankshaft one revolution (360 degrees). Check intake valve clearance on cylinders No. 3 and 4 and exhaust valves on cylinders No. 2 and 4. Adjust valve clearance if it is not within specification. See VALVE CLEARANCE SPECIFICATIONS table.
  5. To adjust valve clearance, rotate crankshaft until camshaft lobe is pointing upward, away from adjuster shim. Install Spring Compressor (J-37141-1) between camshaft and adjuster shim to push lifter downward. See Fig 1 .
    Fig 1: Adjusting Valve Clearance
    G50J07256Courtesy of GENERAL MOTORS CORP.
  6. Insert Lifter Detainer (J-37141-2A) between camshaft and lifter. Ensure bottom edge of lifter detainer is positioned on lifter and not the adjuster shim. See Fig 1 . This will hold lifter away from camshaft.
  7. Remove spring compressor. Using small screwdriver and magnet, remove adjuster shim. Replacement adjuster shim thickness can be determined by using adjuster shim charts. See Fig 2 and Fig 3 . Adjuster shim thickness can also be determined by using following formula: N = T + A
    • N = Thickness of adjuster shim required.
    • T = Thickness of adjuster shim removed.
    • A = Measured clearance minus valve clearance specification.
  8. For example, on intake valves, N= T + A - .008" (.20 mm). To install new adjuster shim, depress valve spring using spring compressor. Install adjuster shim. Remove lifter detainer and spring compressor.
  9. Ensure valve clearance is within specification. To install remaining components, reverse removal procedure.
Fig 2: Determining Exhaust Valve Adjuster Shim
G91B17054Courtesy of GENERAL MOTORS CORP.
Fig 3: Determining Intake Valve Adjuster Shim
G91C17055Courtesy of GENERAL MOTORS CORP.
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