Piston And Connecting Rod Measurement Procedure

Piston Pin To Connecting Rod Bore And Piston Bore Clearance

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.

Piston Ring Clearance

1. Courtesy 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 piston compression upper ring end gap. Place the piston ring in the area of the bore where the piston ring will travel approximately 5 mm (0.2 in) down from the deck surface. Refer to Engine Mechanical Specifications  for the correct value of the clearance.
   • The piston compression lower 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 piston oil ring end gap. Place the piston ring in the area of the bore where the piston ring will travel approximately 13 mm (0.5 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. Courtesy of GENERAL MOTORS COMPANY

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

   • The piston compression upper ring end gap. Refer to Engine Mechanical Specifications  for the correct value of the clearance.
   • The piston compression lower ring end gap. Refer to Engine Mechanical Specifications  for the correct value of the clearance.
   • The piston oil ring end gap. Refer to Engine Mechanical Specifications  for the correct value of the clearance.
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.

Piston Measurement

1. Measure the engine cylinder bore. Engine Mechanical Specifications 

2. Courtesy of GENERAL MOTORS COMPANY

   Measure the piston at 3 measure points from the bottom of the skirt, with a micrometer or caliper at a right angle to the piston.

   1. First measure point a1 = 8.9 mm (0.35 in) from the bottom of the skirt.
   2. Second measure point a2 = 22.8 mm (0.9 in) from the bottom of the skirt.
   3. Third measure point a3 = 41.1 mm (1.62 in) from the bottom of the skirt.
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.

Connecting Rod Bearing Clearance with Micrometer Gauge Internal Measuring Device

1. Install the connecting rod bearings and the connecting rod bearing caps.
2. Tighten the connecting rod bolts:
   CAUTION:

   Fastener Caution

   CAUTION:

   Torque-to-Yield Fastener Warning

   1. First Pass: 20 N.m (15 lb ft)
   2. Final Pass: 60 degrees - Use the special tool: EN-45059-A  Angle Meter

3. Courtesy of GENERAL MOTORS COMPANY

   Using a suitable tool, measure the connecting rod bearing diameters (1) at 3 points as shown. Record the results as measurement a, measurement b, and measurement c.

4. Calculate the average connecting rod inner diameter.

   Formula: (measurement a + measurement b + measurement c) / 3

5. Courtesy of GENERAL MOTORS COMPANY

   Using a suitable tool, measure the connecting rod journal (1) diameter, and record the result as measurement a. Measure the diameter a second time 90 degrees from the first measurement. Record the result as measurement b.

6. Calculate the average connecting rod journal diameter.

   Formula: (measurement a + measurement b) / 2.

7. Subtract the average connecting rod journal diameter from the average connecting rod inner 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.