GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 Sonoma Pickup - 2WD 🢒 Engine 🢒 Engine Mechanical - 4.3L 🢒 Piston, Connecting Rod, and Bearing Cleaning and Inspection

Important: Measurement of all components should be taken with the components at room temperature.

Do not use a wire brush in order to clean any part of the piston.


    Object Number: 34671 Size: SH

    Caution: Wear safety glasses in order to avoid eye damage.

  1. Clean the piston and connecting rod in solvent.
  2. Dry the components with compressed air.

    3. Object Number: 4977 Size: SH
  3. Clean the piston ring grooves with a suitable ring groove cleaning tool.
  4. Clean the piston oil lubrication holes and slots.

    5. Object Number: 156168 Size: SH
  5. Inspect the piston for the following:
    6. • Eroded areas (1) on the top of the piston
    • Scuffed or damaged skirt (2)
    • Damage to the pin bore (3)
    • Cracks in the piston ring lands, the piston skirt, or the pin bosses
    • Piston ring grooves for nicks, burrs, or other warpage which may cause the piston ring to bind
  6. Inspect the piston pin for scoring, wear or other damage.

    7. Object Number: 4969 Size: SH
  7. Measure the piston ring-to-piston ring groove side clearance.
    8. 7.1. Insert the edge of the piston ring into the piston ring groove.
    7.2. Roll the piston ring completely around the piston.
       • If binding is caused by a distorted piston ring groove, MINOR imperfections may be removed with a fine file.
       • If binding is caused by a distorted piston ring, replace the piston ring.

    Object Number: 22934 Size: SH
  8. Measure the piston ring side clearance with a feeler gauge.
  9. If the side clearance is too small, try another piston ring set.
  10. If the proper piston ring-to-piston ring groove clearance cannot be achieved, replace the piston and pin assembly.
  11. To determine the proper piston ring side clearance, refer to Engine Mechanical Specifications .

    12. Object Number: 4976 Size: SH
  12. To determine piston pin-to-bore clearance use a micrometer and measure the piston pin.

    13. Object Number: 4975 Size: SH
  13. To determine piston pin-to-bore clearance, use an inside micrometer and measure the piston pin bore.
  14. To determine the piston pin-to-bore clearance, subtract the piston pin diameter from the piston pin bore diameter. Refer to Engine Mechanical Specifications .

    15. Object Number: 188016 Size: SH
  15. Measure the piston for out-of-round.
    16. 15.1. With a micrometer at a right angle to the piston, measure the piston at 11 mm (0.433 in) from the bottom of the skirt.
    15.2. Measure the piston at three different points 120 degrees apart and compare the readings, refer to Engine Mechanical Specifications .
    15.3. If the clearance is not within specifications, replace the piston and pin as an assembly.

    Object Number: 156167 Size: SH
  16. Inspect the connecting rod for an out-of-round bearing bore.

    17. Object Number: 156169 Size: SH
  17. Inspect the connecting rod for twisting.
  18. Inspect the connecting rod for damage to the bearing cap stud threads.

    19. Object Number: 4968 Size: SH
  19. Measure the piston compression ring end gap.

    20.         Important: Fit each compression ring to the cylinder in which it will be used.

    19.1. Place the compression ring into the cylinder bore.
    19.2. Push the compression ring into the cylinder bore to approximately 6.5 mm (0.25 in) above the ring travel.

    The ring must be square to the cylinder wall.

    19.3. Use a feeler gage in order to measure the end gap.
    19.4. Select another size ring set if the end gap exceeds specifications.