GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2008 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Engine 🢒 Engine Mechanical - 7.8L 🢒 Cylinder Head Cleaning and Inspection
  1. Clean carbon from all of the valve ports and combustion chambers.
  2. Clean valve guide and bore of dirt and carbon.

    3. Important: Do not use a wire wheel. Remove all traces of the old gasket material.

  3. Clean the valve stems and heads.
  4. Inspect the cylinder head for cracks or damaged threaded holes.
  5. Inspect the cylinder head gasket mating surfaces for damage.
  6. Inspect the valves for damage.
  7. Inspect the valve seats for damage.

    8. Object Number: 736729 Size: SH

    Important: Do not resurface the cylinder head.

  8. Measure the cylinder head for flatness. Check in six different directions. If the cylinder head is distorted more than 0.2 mm (0.0078 in), replace the cylinder head.

    9. Object Number: 736732 Size: SH
  9. Measure installed depth. If the measurement is more than 2.5 mm (0.098 in) for the intake valve and 2.8 mm (0.110 in) for the exhaust valve, replace the valve or the valve seat as required.

    10. Object Number: 736735 Size: SH
  10. Measure the valve stem diameter.
    11. • Production specification for the intake valve: 7.946-7.961 mm (0.3128-0.3134 in).
    • Service limit: 7.88 mm (0.3102 in).
    • Production specification for the exhaust valve: 7.921-7.936 mm (0.3118-0.3124 in).
    • Service limit: 7.88 mm (0.3102 in).
  11. Measure the valve guide inside diameter.
  12. Measure the valve guide to valve stem clearance.

    13. Object Number: 736737 Size: SH
  13. Locate the dial indicator so that the plunger is 10 mm (0.39370 in) above the valve guide.
  14. Hold the valve on its seat.
  15. Move the valve stem from side to side to obtain the clearance reading.
    16. • Production specification for the intake valve guide: 0.04-0.07 mm (0.0016-0.0028 in).
    • Service limit: 0.2 mm (0.0079 in).
    • Production specification for the exhaust valve guide: 0.06-0.1 mm (0.0024-0.0039 in).
    • Service limit: 0.25 mm (0.0098 in).

    Object Number: 736738 Size: SH
  16. Measure the valve spring length.
    17. • Production specification for the intake valve spring: 65.9 mm (2.5945 in).
    • Service limit: 64.8 mm (2.5512 in).
    • Production specification for the exhaust spring: 68.1 mm (2.6811 in).
    • Service limit: 66.9 mm (2.6339 in).

    Object Number: 736740 Size: SH
  17. Measure the valve spring tension. Compress the valve springs to the specified height.
    18. • Specified height 46 mm (1.8110 in) length.
    • Intake production: 348.1 N (78.3 lb)
    • Service limit: 296 N (67 lb)
    • Exhaust production: 382.5 N (86 lb)
    • Service limit: 325 N (73 lb)
  18. If the valve springs are not within factory specifications, replace the valve springs.