GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1996 🢒 Lumina 🢒 Engine 🢒 Engine Mechanical - 3.4L (VIN X) 🢒 Piston and Connecting Rod Inspection

    Caution: Bodily injury may occur if carburetor cleaning fluid is exposed to the skin or if the fumes are inhaled.

  1. Clean the following components of sludge and carbon:
    2. • The piston
    • The piston pin
    • The connecting rod
  2. Clean the piston ring grooves of carbon to the bare metal.
  3. Clean any varnish from the piston pin. Do this by soaking the piston pin in a carburetor cleaning solution. Do not scrape the piston skirt.
  4. Inspect the connecting rod for bending or twisting using the following procedure:
    5. 4.1. Install the connecting rod cap.
    4.2. Place the connecting rod assembly on a checking fixture. Check for bending or twisting.
    4.3. Do not attempt to straighten the connecting rod. If the connecting rod is bent or twisted, replace the connecting rod.
       • The connecting rods should not be bent more than 0.18 mm (0.007 in) for every 76.2 mm (3.00 in) of rod length.
       • The connecting rods should not be twisted more than 0.038 mm (0.0015 in) for every 25.4 mm (1.00 in) of rod length.
    4.4. Check new connecting rods before using them.
  5. Inspect the outside of the connecting rod bearing and the ID of the connecting rod lower end for wear indicating high spots in the connecting rod lower end.
  6. Inspect the upper end of the connecting rod for scoring.
  7. Inspect the piston pin for the following conditions:
    8. • Scoring
    • Galling caused by improper installation
    • Fit in connecting rod and piston
  8. Inspect the piston for the following conditions:
    9. • Scoring of the skirt
    • Cracks
    • Broken ring groove lands
    • Wear

    Object Number: 4988 Size: SH

    Important: When fitting pistons, both the piston and the cylinder bore condition must be considered together. Production and service pistons have the same nominal weight and can be intermixed without affecting engine balance. If necessary, used pistons may be fitted selectively to any cylinder of the engine, providing they are in good condition and the same weight.

    Do not cut oversize pistons down or the engine balance will be affected.

  9. Measure the piston diameter.
  10. When measuring the piston for size or taper, make the measurement with the piston pin removed. If the piston is worn or damaged, replace the piston with a standard or oversize piston.

    11. Object Number: 4972 Size: SH

    Important: Finish hone when selecting the piston.

  11. Measure the cylinder bore with a telescoping gage. If the cylinder bore is worn beyond specifications, rebore and hone the cylinder bore to size.
  12. Subtract the piston diameter from the cylinder bore diameter to determine the piston-to-bore clearance. Refer to Engine Mechanical Specifications .
  13. Compare the piston-to-bore clearance with the specifications in order to determine if the clearance is in the acceptable range.
  14. If the used piston is not acceptable, check the service piston sizes. Determine if a new piston can be selected. Service pistons are available in standard, and several oversizes.
  15. If you must recondition the cylinder bore, measure the new piston diameter. Then hone the cylinder bore to the correct clearance.
  16. Select a new piston.
  17. Mark the piston in order to identify the cylinder for which the piston was fitted.
  18. Measure the piston pin bore diameter with an inside micrometer.
  19. Measure the piston pin diameter with a micrometer.
  20. Subtract the piston pin bore diameter from the piston pin diameter in order to determine the clearance. Refer to Engine Mechanical Specifications .
  21. If the clearance is not acceptable, replace the piston assembly.

    22. Object Number: 4968 Size: SH

    Important: Do not reuse piston rings. Fit rings to match the cylinder they will be used in.

  22. Measure the piston compression ring end gap using the following procedure:
    23. 22.1. Place the piston into the cylinder at the bottom of the ring travel.
    22.2. Place a piston ring on top of the piston.
    22.3. Back off the piston.
    22.4. Measure the ring gap. If the gap is below specification, increase the gap by carefully filing off excess material. Refer to Engine Mechanical Specifications .

    Important: Do not attempt to cut the ring groove, although high spots in the ring groove may be cleaned up by careful use of a point file.

  23. Measure the piston compression ring side clearance using the following procedure:
    24. 23.1. Roll the piston ring around the groove in which it is to be installed.
    23.2. Measure the side clearance. If the ring is too thick, try another ring. Refer to Engine Mechanical Specifications .