Piston And Connecting Rod Measurement Procedure

Piston Pin To Connecting Rod Bore And Piston Bore Clearance

1. Measure clearance between piston pin and 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 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 clearance between piston pin and 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 piston.
5. If there is excessive clearance, replace the piston pin.
6. If there is still excessive clearance, replace the piston.

Piston Ring Clearance

Fig 1: Measuring Piston Ring End Clearance
Courtesy of GENERAL MOTORS COMPANY
1. 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. Refer to Engine Mechanical Specifications  for the correct value of the clearance.
   • The lower compression ring end gap. Refer to Engine Mechanical Specifications  for the correct value of the clearance.
   • The oil scraper ring end gap. 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.
Fig 2: Measuring Piston Ring Side Clearance
Courtesy of GENERAL MOTORS COMPANY
3. Measure the piston ring axial clearance as shown (1). Compare the measurements with those provided below:
   • The upper compression ring end gap. Refer to Engine Mechanical Specifications  for the correct value of the clearance.
   • The lower compression ring end gap. Refer to Engine Mechanical Specifications  for the correct value of the clearance.
   • The oil scraper 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 to Engine Block Cylinder Bore Clearance

1. Measure the engine cylinder bore. Refer to Engine Block Cleaning and Inspection .
Fig 3: Outside Micrometer And Piston
Courtesy of GENERAL MOTORS COMPANY
2. Measure the piston (1) 10 mm (0.3937 in) from the bottom of the skirt, with a micrometer (2) or caliper at a right angle to the piston.
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 specification, replace the piston.

Connecting Rod Bearing Clearance (with Micrometer Gauge Internal Measuring Device)

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 .

   NOTE:

   The old bolts can be reused for the measuring procedure.

   1. Tighten the connecting rod bearing cap bolts a first pass to 25 N.m (18 lb ft).
   CAUTION:

   Refer to Torque-to-Yield Fastener Caution .

   2. Tighten the bolts a final pass an additional to 110 degrees using the EN-45059  meter.
Fig 4: Measuring Connecting Rod Bearing Diameters
Courtesy of GENERAL MOTORS COMPANY
3. Measure the connecting rod bearing diameters at 3 points as shown (1). Use a internal measuring device.
4. Calculate the average connecting rod inner diameter.

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

Fig 5: Connecting Rod Journal Diameter Points
Courtesy of GENERAL MOTORS COMPANY
5. 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.