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Home >> Cadillac >> 2021 >> CT4 V, 4WD >> Repair and Diagnosis >> Engine Mechanical >> Mechanical >> Engine Mechanical - 2.7L (L3B) - Repair Instructions - Ct4 (5 Of 6) >> Piston and Connecting Rod Overhaul >> Piston And Connecting Rod Measurement Procedure

Piston And Connecting Rod Measurement Procedure

  1. Measure the clearance between the piston pin and the connecting rod bore. Use the following procedure:
    1. Measure the piston pin outside diameter.
    2. Measure the connecting rod bore diameter.
    3. Substract the piston pin outside diameter from the connecting rod diameter to calculate the clearance.
    4. Refer to the ENGINE MECHANICAL SPECIFICATIONS for the correct value of the clearance piston pin in the connecting rod.
  2. If there is excessive clearance, replace the piston pin.
  3. If there is still excessive clearance, replace the connecting rod.
  4. Measure the clearance between the piston pin and the piston bore. Use the following procedure:
    1. Measure the piston pin outside diameter.
    2. Measure the piston bore diameter.
    3. Substract the piston pin outside diameter from the piston bore diameter to calculate the clearance.
    4. Refer to ENGINE MECHANICAL SPECIFICATIONS for the correct value of the clearance piston pin in the piston.
  5. If there is excessive clearance, replace the piston pin.
  6. If there is still excessive clearance, replace the piston.
  1. GM5030915Courtesy of GENERAL MOTORS COMPANY

    Install the piston rings to the cylinder as shown (1) and measure the piston ring end gap. Compare the measurements with those provided below:

    • The upper compression ring end gap. Place the piston ring in the area of the bore where the piston ring will travel approximately 10 mm (0.4 in) down from the deck surface. Refer to ENGINE MECHANICAL SPECIFICATIONS for the correct value of the clearance.
    • The lower compression ring end gap. Place the piston ring in the area of the bore where the piston ring will travel approximately 18 mm (0.7 in) down from the deck surface. Refer to ENGINE MECHANICAL SPECIFICATIONS for the correct value of the clearance.
    • The oil scraper ring end gap. Place the piston ring in the area of the bore where the piston ring will travel approximately 23 mm (0.9 in) down from the deck surface. Refer to ENGINE MECHANICAL SPECIFICATIONS for the correct value of the clearance.
  2. If the clearance is greater than the provided specifications, the piston rings must be replaced.
  3. GM5030917Courtesy of GENERAL MOTORS COMPANY

    Measure the piston ring axial clearance as shown (1). Compare the measurements with those provided below:

  4. If the clearance is greater than the provided specifications, replace the piston rings.
  5. If the clearance is still to great, replace the pistons.
  1. Measure the engine cylinder bore. ENGINE MECHANICAL SPECIFICATIONS
  2. GM5030916Courtesy of GENERAL MOTORS COMPANY

    Measure the width of the piston (1) at 30 mm (1.181 in) below the crown, top, at the thrust surfaces of the piston, perpendicular to the piston pin centerline.

  3. Subtract the piston diameter from the cylinder bore diameter in order to calculate the piston-to-bore clearance.
  4. Refer to ENGINE MECHANICAL SPECIFICATIONS for the correct value of the clearance piston-to-bore.
  5. If the clearance obtained through measurement is greater than these specifications and the cylinder bores are within the specification, replace the piston.
  1. Install the connecting bearings and the connecting rod bearing caps.
  2. Tighten the connecting rod bearing cap bolts in the following sequence:
      CAUTION:

      Refer to Fastener Caution

      CAUTION:

      Refer to TORQUE-TO-YIELD FASTENER CAUTION

    1. First Pass: 25 N.m (18 lb ft)
    2. Final Pass: 75 degrees - Use the special tool: EN-45059  Angle Meter
  3. GM2189741Courtesy of GENERAL MOTORS COMPANY

    Measure the connecting rod bearing diameters at 3 points as shown (1). Use an internal measuring device.

  4. Calculate the average connecting rod inner diameter.

    Formula: (1. result + 2. result + 3. result) / 3

  5. GM2189634Courtesy of GENERAL MOTORS COMPANY

    Measure the connecting rod journal diameter at 2 points between (1) and (3) and between (2) and (4). Use a micrometer gauge.

  6. Calculate the average connecting rod journal diameter.

    Formula: (1. result + 2. result) / 2.

  7. Subtract the average connecting rod journal diameter from the average connecting rod bearing diameter in order to determine the connecting rod bearing clearance.
  8. Refer to ENGINE MECHANICAL SPECIFICATIONS for the correct value of the connecting rod bearing clearance.
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