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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1443 (Engine Mechanical - 4.2L (Ll8)) >> Repair Instructions >> Off-Vehicle Repair Instructions >> Cylinder Head Cleaning And Inspection >> Cleaning and Inspection

Cleaning and Inspection

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    Fig 1: View Of Cylinder Head Gasket
    GM637586Courtesy of GENERAL MOTORS CORP.
  1. Inspect the cylinder head gasket and the mating surface. Inspect for leaks, corrosion, and blowby.
    2. Fig 2: Checking Cylinder Head Warpage
    GM637705Courtesy of GENERAL MOTORS CORP.
  2. If the gasket failed, determine the cause. The following conditions may cause gasket failure:
    • Improper installation
    • Warped cylinder head
    • Missing or not fully seated dowel pins
    • Low torque on the cylinder head bolts
    • Incorrect length cylinder head bolts
    • A warped engine block surface
    • Scratched surfaces
    • Foreign material
    • Cracked engine block threaded holes
  3. Clean the following components:
    • The gasket surfaces

      Do not use a motorized brush on the head gasket sealing surface.

    • Valve stems and valve heads
    • The bolt hole threads

      Remove all dirt, debris, or threadlocking material from the bolt holes.

  4. Inspect the cylinder head mating surfaces for flatness. Use a feeler gauge and a straight edge.
  5. Replace the cylinder head if warped more than 0.08 mm (0.003 in).
  6. Inspect the cylinder head for cracks.
    7. IMPORTANT: Do not attempt to weld the cylinder head. If the cylinder head is damaged, replace the cylinder head. Minor nicks may be repaired with a fine flat file or emery cloth.
  7. Inspect the cylinder head deck for corrosion.
    8. Fig 3: Measuring Valve Spring Tension
    GM4960Courtesy of GENERAL MOTORS CORP.
  8. Inspect the valve springs for squareness.
  9. Use J 9666  to measure the valve spring tension. Replace the valve spring if the tension is not within specification.
    10. Fig 4: Inspecting Valves
    GM715593Courtesy of GENERAL MOTORS CORP.
  10. Inspect the valve guides for wear. The valve guides may be reamed oversized 0.075 mm (0.003 in) and oversized stemmed valves may be installed. The same size valve seal should be used.
  11. Inspect the valve seats for excessive wear, damage, or hot spots.
  12. Use the following procedure to measure the valve seat concentricity:
    1. Lift the valve off the valve seat.
    2. Apply a dab of blue dye to the valve face.
    3. Seat and rotate the valve. The blue dye traces transferred to the valve seat are an indication of concentricity of the valve seat.
  13. Use the following procedure to measure the valve runout:
    1. Clean off the blue dye.
    2. Apply blue dye to the valve seat.
    3. Seat and rotate the valve.
    4. The traces of blue dye transferred to the valve indicates valve runout.
  14. Replace the head if the valve seats are damaged.
  15. Inspect the valves for the following damage:
    • Grooving (1, 2)
    • Bent valve stem (3). Replace any bent valve.
    • Burrs or scratches (4). Minor burrs or scratches may be removed with a fine oil stone.
    • Chipped or worn key grooves (5). Replace if damaged.
    • Valve tip wear (6). Replace if worn.
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