GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2008 🢒 Cobalt 🢒 Engine 🢒 Engine Mechanical - 2.0L 🢒 Piston, Connecting Rod, and Bearing Cleaning and Inspection

Connecting Rod Measurement

    Object Number: 479859 Size: SH
  1. Clean the connecting rods in solvent and dry with compressed air.
  2. Inspect the connecting rods for the following conditions:
    3. • Signs of being twisted, bent, nicked, or cracked
    • Scratches or abrasion on the rod bearing seating surface
  3. If the connecting rod bores contain minor scratches or abrasions, clean the bores in a circular direction with a light emery paper. DO NOT scrape the rod or rod cap.
  4. If the beam of the rod is scratched or has other damage replace the connecting rod.
  5. Measure the piston pin to connecting rod bore using the following procedure:
    6. 5.1. Using an outside micrometer, take two measurements of the piston pin in the area of the connecting rod contact.
    5.2. Using an inside micrometer, measure the connecting rod piston pin bore.
    5.3. Subtract the piston pin diameter from the piston pin bore diameter.
    5.4. The clearance should not be more than 0.021 mm (0.0008 in).
  6. If there is excessive clearance, replace the piston pin.
  7. If there is still excessive clearance, replace the connecting rod.

Piston Measurement

    Object Number: 1825054 Size: SH
  1. Clean the piston skirts and the pins with a cleaning solvent. DO NOT wire brush any part of the piston.
  2. Clean the piston ring grooves with a groove cleaner. Ensure the oil ring holes and slots are clean.
  3. Inspect the pistons for the following conditions:
    4. • Cracked ring lands, skirts, or pin bosses
    • Ring grooves for nicks, burrs that may cause binding
    • Warped or worn ring lands
    • Eroded areas at the top of the piston (1)
    • Scuffed or damaged skirts (2)
    • Worn piston pin bores (3)
  4. Replace pistons that show any signs or damage or excessive wear.
  5. Measure the piston pin bore to piston pin clearances using the following procedure:
    6. 5.1. Piston pin bores and pins must be free of varnish or scuffing.
    5.2. Use an outside micrometer to measure the piston pin in the piston contact areas.
    5.3. Using an inside micrometer, measure the piston pin bore.
    5.4. Subtract the measurement of the piston pin bore from the piston pin. The clearance should be within 0.002-0.012 mm (0.00007-0.00047 in).
    5.5. If the clearance is excessive, determine which component is out of specification.

    Object Number: 4968 Size: SH
  6. Measure the piston ring end gap using the following procedure:
    7. 6.1. Place the piston ring in the area of the bore where the piston ring will travel, approximately 25 mm or 1 inch down from the deck surface. Ensure the ring is square with the cylinder bore by positioning the ring with the piston head.
    6.2. Measure the end gap of the piston ring with feeler gages. Compare the measurements with those provided below:

    Specification

        • The top compression ring end gap should be 0.20-0.35 mm (0.0078-0.0138 in).
        • The second compression ring end gap should be 0.35-0.55 mm (0.0137-0.0216 in).
        • The oil ring end gap should be 0.25-0.76 mm (0.0098-0.029 in).
    6.3. If the clearance exceeds the provided specifications, the piston rings must be replaced.
    6.4. Repeat the procedure for all the piston rings.

    Object Number: 1769823 Size: SH
  7. Measure the piston ring side clearance using the following procedure:
    8. 7.1. Roll the piston ring entirely around the piston ring groove. If any binding is caused by a distorted piston ring, replace the ring.
    7.2. With the piston ring on the piston, use feeler gages to measure clearance at multiple locations.
    7.3. The clearance between the surface of the top piston ring and the ring land should be no greater than 0.055 mm (0.0022 in).
    7.4. If the clearance is greater than specifications, replace the piston ring.
    7.5. If the new ring does not reduce the top ring side clearance to 0.055 mm (0.0022 in) or less, install a new piston.
  8. The top compression ring may be installed with either side up. There is a locating dimple on the second compression ring near the end for identification of the top side. Install the second compression ring with the dimple facing up.
  9. The clearance between the surface of the second piston ring and the ring land should be no greater than 0.032 mm (0.0012 in).
  10. If the new ring does not reduce the clearance to 0.032 mm (0.0012 in) or less, install a new piston.

    11. Object Number: 4988 Size: SH
  11. Measure piston width using the following procedure:
    12. 11.1. Using an outside micrometer, measure the width of the piston 12.5 mm (0.4925 in) above the bottom of the piston skirt at the thrust surface perpendicular to the centerline of the piston pin.
    11.2. Compare the measurement of the piston to its original cylinder by subtracting the piston width from the cylinder diameter.
    11.3. The proper clearance specification for the piston is 0.010-0.041 mm (0.0006-0.0016 in).
  12. If the clearance obtained through measurement is greater than these specifications and the cylinder bores are within specification, replace the piston.

Piston Selection

    Object Number: 4972 Size: SH

    Important: 

       • Measurements of all components should be taken with the components at normal room temperature.
       • For proper piston fit, the engine block cylinder bores must not have excessive wear or taper.
       • A used piston and pin set may be reinstalled if, after cleaning and inspection, they are within specifications.

  1. Inspect the engine block cylinder bore. Refer to Engine Block Cleaning and Inspection.
  2. Inspect the piston and the piston pin. Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection.
  3. Using a bore gage, measure the cylinder bore diameter. Measure at a point 64 mm (2.5 in) from the top of the cylinder bore.

    4. Object Number: 4974 Size: SH
  4. Measure the bore gage with a micrometer and record the reading.

    5. Object Number: 4988 Size: SH
  5. With a micrometer or caliper at a right angle to the piston, measure the piston 14 mm (0.570 in) from the bottom of the skirt.
  6. Subtract the piston diameter from the cylinder bore diameter in order to determine piston-to-bore clearance.
  7. For proper piston-to-bore clearance. Refer to Engine Mechanical Specifications.
  8. If the proper clearance cannot be obtained, select another piston and measure for the clearances.
  9. If the proper fit cannot be obtained, hone the cylinder bore or replace the cylinder block.
  10. When the piston-to-cylinder bore clearance is within specifications, mark the top of the piston using a permanent marker for installation to the proper cylinder. Refer to Separating Parts.