Connecting Rod: Service and Repair

Engine bearings are precision insert bearings, which are available for service use in standard and 0.001 in undersize.

Notice: Do not scrape, shim, or file bearing inserts. If the bearing surface of the insert is touched with bare fingers, the skin oil and acids will etch the bearing surface.





1. Inspect the bearing surfaces for the following conditions:
- Wear
- Gouges
- Embedded foreign material
- If foreign material is present, determine the nature and the source of the foreign material.
- Inspect the oil pan sludge and residue.
- Uneven side-to-side wear, resulting from a bent crankshaft or tapered bearing journals.
2. Inspect the outer surfaces for the following conditions:
- Spot wear, resulting from insert movement or high spots in the surrounding material
- Discoloration, resulting from overheating
- Flattened tangs and wear grooves, resulting from looseness or rotation

Important:
- Carefully inspect bearing failure, other than normal wear.
- Inspect the crankshaft or the connecting rod and the bearing bores.
- Use the following procedure, in order to inspect the connecting rods or main bearing bores:
- Torque the bearing cap to specifications.
- Measure the bore for taper and out of round.
- Ensure that taper or out of round does not exist.
3. Inspect the thrust surfaces of the main thrust bearing for the following conditions:
- Wear
- Grooving, as a result of irregularities in the crankshaft thrust surface
4. Inspect the bearing cap bolts.
- In order to determine if a bolt is stretched, compare it to a new bolt.
- Replace the bearing cap bolts, as necessary.

Bearing Clearance
In order to determine the correct replacement insert size, accurately measure the bearing clearance. Use either of the following methods to measure the bearing clearance however, the first method gives more reliable results than the second method.
1. This method yields measurements from which to compute the bearing clearance.
1.1. Measure the crankshaft journal diameter, in several places, approximately 90 degrees apart.
1.2. Average the crankshaft journal diameter measurements.
1.3. Measure the taper and runout.
1.4. With the bearing inserts installed in the correct bore and torqued to specification, measure the bearing insert ID with an inside micrometer.
1.5. If new inserts are replacing the inserts, measure after installing the new inserts.
1.6. Select a suitable set of inserts, if the readings are within limits.
- Bearing sets are available in standard and undersize, in order to keep clearances within the limits.
- Replace the crankshaft if the clearances cannot be brought into specifications.
2. This method yields the bearing clearance directly, however it does not give any indication of bearing or journal runout.
2.1. Install all of the bearing inserts into the block.
2.2. Install the crankshaft into the block.
2.3. Place a piece of gauging plastic across the entire bearing width.
2.4. Seat the bearing cap carefully, by tapping it lightly with a suitable tool.

Important: Do not rotate the crankshaft.

2.5. Torque the bearing cap bolts to specification.
2.6. Remove the bearing cap, leaving the gauging plastic in place, regardless of whether the gauging plastic adheres to the journal or to the bearing cap.
2.7. Measure the flattened gauging plastic, at its widest point, with the scale printed on the gauging plastic package.
2.8. Remove all traces of the gauging plastic after measuring.

Bearing Installation

Notice: Do not scrape, shim, or file bearing inserts. If the bearing surface of the insert is touched with bare fingers, the skin oil and acids will etch the bearing surface.

Important: Ensure that the bearing cap bolt hole and the cap mating surfaces are clean and dry.

1. Dip the bearing cap bolts in clean engine oil.
2. Place the inserts into the bearing cap and into the connecting rod.
- The inserts will project slightly when put into place. Ensure that they project an equal distance on both sides.
- Ensure the engagement of the insert tangs.

Notice: Upper and lower inserts may be different. Do not obstruct any oil passages.

3. When using a thrust bearing main bearing insert, coat the thrust surface with GM-approved lubricant or equivalent.
4. Lubricate the bearing surface with clean engine oil.
5. Install the connecting rod.
6. Install the bearing cap, by tapping the cap gently into place with a suitable tool.

Notice: Refer to Fastener Notice in Service Precautions.

7. Install the bearing cap bolts.
- Tighten the bearing cap bolts to 35 Nm + 45 degrees (26 ft. lbs. + 50 degrees).

8. Pry the connecting rods back and forth, in order to check for binding.
9. If necessary, loosen and retighten the bearing cap.





10. Measure the connecting rod side clearance.