Connecting Rod Measurement

1. Using an outside micrometer, take two measurements of the piston pin in the area of the connecting rod contact.
2. Using an inside micrometer, measure the connecting rod piston pin bore.
Fig 1: Measuring Connecting Rod Piston Pin Bore
Courtesy of GENERAL MOTORS CORP.
3. Subtract the piston pin diameter from the piston pin bore.
4. Compare the clearance measurements with the Engine Mechanical Specifications .
5. If the clearance is excessive, replace the piston pin. If a new pin does not resolve the clearance problem, replace the connecting rod.

Important:  Measurements of all components should be taken with the components at normal room temperature.

For proper piston fit, the engine block cylinder bores should 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.
2. Inspect the piston and pin.
3. Use the J 8087  and measure the cylinder bore diameter. Measure at a point 64 mm (2.5 in) from the top of the cylinder bore.
4. Measure the J 8087  with a micrometer and record the reading.
   Fig 2: Measuring Cylinder Bore Diameter

   Courtesy of GENERAL MOTORS CORP.
5. With a micrometer or caliper at a right angle to the piston, measure the piston 11 mm (0.433 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. Refer to Engine Mechanical Specifications .
7. If the proper clearance cannot be obtained, select another piston and measure the clearances.
8. When the piston-to-cylinder bore clearance is within specifications, permanently mark the top of the piston for installation into the proper cylinder.
   Fig 3: Measuring Piston Clearances

   Courtesy of GENERAL MOTORS CORP.