Crankshaft Main Bearing: Service and Repair

CONNECTING ROD AND MAIN BEARINGS

Depending upon crankshaft condition, bearings may be replaced in the vehicle or the engine must be removed. If the engine must be removed, follow the crankshaft procedure. Evaluate bearings. If the engine is out of the vehicle and upside down, the crankshaft will rest on the upper bearings and the total clearance can be measured between the lower bearing and journal. If
the engine is to remain in the vehicle, the crankshaft must be supported upward to remove any clearance from the upper bearing. The total clearance can then be measured between the lower bearing and journal.







Engine bearings are of the precision insert type. They are available for service use in standard and various undersizes.

Note: Bearing inserts must not be shimmed, scraped or filed. Do not touch the bearing surface of the insert with bare fingers. Skin oil and acids will etch the bearing surface.

Inspect

1. Bearing surfaces for:
- Wear.
- Gouges.
- Embedded foreign material. If foreign material is found, determine its nature and source. Inspect oil pan sludge and residue.
- Uneven side-to-side wear. if uneven wear is found, check for a bent crankshaft or tapered bearing journals.

2. Outer surfaces for:
- Wear. Surface wear indicates either movement of the insert or high spots in the surrounding material (spot wear).
- Overheating (discoloration).
- Looseness or rotation (flattened tangs and wear grooves).

3. Thrust surfaces (main thrust bearing) for:
- Wear
- Grooving. Grooves are caused by irregularities of the crankshaft thrust surface.


Important

- Bearing failure, other than normal wear, must be investigated carefully. Inspect the crankshaft or connecting rod and the bearing bores.
- To inspect connecting rods or main bearing bores:

a. Tighten the bearing cap to specifications.






b. Measure the bore for taper and out of round using J 8087.
c. No taper or out of round should exist.

Measure

- Bearing clearance. To determine the correct replacement insert size, the bearing clearance must be measured accurately. Either of the following two methods may be used, however, method "A" gives more reliable results and is preferred.

Important

Method "A" yields measurements from which the bearing clearance can be computed. Method "B" yields the bearing clearance directly. Method "B" does not give any indication of bearing run-out.

Do not mix inserts of different nominal size in the same bearing bore.

Method "A"

1. Measure the crankshaft journal diameter with a micrometer in several places, approximately 9O° apart, and average the measurements.
2. Measure taper and run-out.
3. Install bearing inserts and tighten rod and main bearing cap bolts to specification.
4. Measure inside bearing diameter of crankshaft bores with an inside micrometer.

- Subtract the crankshaft journal diameter from the crankshaft bearing bore diameter to determine crankshaft bearing clearance.

5. Measure the inside bearing diameter of the connecting rod in the same direction as the length of the rod.

- Subtract the connecting rod journal diameter from the connecting rod bearing bore diameter to determine connecting rod bearing clearance.

Important

- The bearing cap must be tightened to specification when the measurement is taken.
- Select a suitable set of inserts to provide specified clearance limits. If the specified clearances cannot be met, the crankshaft journal must be reconditioned and undersized bearing inserts installed.

Method "B"

1. Clean and install the used bearing inserts.
2. Place a piece of gaging plastic across the entire bearing width.

Note: In order to prevent the possibility of cylinder block and/or main bearing cap damage, the main bearing caps are to be tapped into their cylinder block cavity using a brass or leather mallet before attaching bolts are installed. Do not use attaching bolts to pull main bearing caps into their seats. Failure to observe this information may damage a cylinder block or bearing cap.

3. Seat the bearing cap carefully by tapping it lightly with a suitable tool.
4. Tighten bearing cap bolts to specification.

Important

- Do not rotate the crankshaft.

5. Remove the bearing cap, leaving the gaging plastic in place. It does not matter whether the gaging plastic adheres to the journal or to the bearing insert.







6. Measure the gaging plastic at its widest paint with the scale printed on the gaging plastic package.
7. Remove all traces of the gaging plastic after measuring.
8. Select a set of bearing inserts that will produce the desired clearance. Replace both bearing shells as a set.

Install

Note: Bearing inserts must not be shimmed, scraped or filed. Do not touch the bearing surface of the insert with the bare fingers. Skin oil and acids will etch the bearing surface.

Important

- Make sure the bearing cap bolt holes and the cap mating surfaces are clean and dry.

1. Dip bearing cap bolts in clean engine oil.

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

2. Place inserts into the bearing cap and into the engine block or connecting rod.

Important

- The inserts will project slightly when put into place. Make sure they project an equal distance on both sides. Make sure the insert tangs are engaged.

3. In the case of a thrust bearing type main bearing insert, coat the thrust surface with GM EOS P/N 1052368 or equivalent.
4. Lubricate the bearing surface with clean engine oil.

Note: Avoid damage to the crankshaft journal. Use connecting rod stud protectors or guide pins.


5. Crankshaft or connecting rod.

Note: In order to prevent the possibility of cylinder block and/or main bearing cap damage, the main bearing caps are to be tapped into their cylinder block cavity using a brass or leather mallet before attaching bolts are installed. Do not use attaching bolts to pull main bearing caps into their seats. Failure to observe this information may damage a cylinder block or bearing cap.

6. Bearing cap. Tap gently into place with a suitable tool.

Apply a small amount of sealer GM P/N 1052942 to the rear of the rear bearing cap sealing surface.







7. With crankshaft bearing and bearing caps installed and both bolts started, thrust crankshaft rearward to set and align bearing caps, then thrust crankshaft forward to align rear face of thrust main bearing. Tighten bolts to specification.

Inspect

- Pry the connecting rods back and forth and check for binding. If necessary loosen and tighten the bearing cap.

Measure






- Crankshaft end play.







- Connecting rod side clearance.

Clean

- Oil pump intake screen.
- Oil pan.

8. Engine oil filter.
9. Fill crankcase with clean engine oil.

Inspect

1. Remove oil pressure sending unit and install an oil pressure gage.
2. Prime engine oil galleries:

- Remove engine oil pump drive unit and rotate oil pump using drill motor and appropriate socket and extension.

Note: If the oil pressure does not build up almost immediately, remove the oil pan and check oil pump suction pipe attachment to the pump. Running the engine without measurable oil pressure will cause extensive damage.

3. Start engine and observe oil pressure.
4. Check for bearing knock. If necessary, disassemble and check for adequate oil supply and proper clearances.