Main Bearing and Rod Bearing Selection

MAIN BEARING AND ROD BEARING SELECTION
Evaluate bearings as specified. If he engine is out of the vehicle and upside down, the cranks~aft 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 (Figure 40).

NOTICE: 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.





4. Connecting rods or main bearing bores as follows:
A. Tighten the bearing cap to specifications.
B. Measure the bore for taper and out of round (Figure 41).
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 measurement 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 journal diameter with a micrometer in several places, approximately 90° apart, and average the measurements.
2. Measure taper and run-out. Refer to "Engine / Specifications" for allowable limits.
3. Install bearing inserts and tighten bearing cap bolts or nuts to specification. Measure ID with an inside micrometer.

Important
^ The bearing cap must be tightened to specification when the measurement is taken.
^ Measure the connecting rod ID in the same direction as the length of the rod.

4. Select a set of bearing inserts that will produce the desired clearance, refer to "Engine / Specifications".
- If the specified clearances cannot be met, the crank shaft journal must be re-conditioned and undersized bearing inserts installed.
- Replace both bearing shells as a set.


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

NOTICE: 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. Bearing cap bolts or nuts.
- Tighten Main bearing cap bolts (19) evenly to 50 N.m (37 lb. ft.).
- Turn main bearing cap bolts (19) evenly an additional 77 degrees using J 36660.
- Rod cap nuts (80) evenly to 50 N.m (37 lb. ft.).

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 cap.





6. Measure the gaging plastic at its widest point with the scale printed on the gaging plastic package (Figure 42).
7. Remove all traces of the gaging plastic after measuring.
8. Select a set of bearing inserts that will produce the desired clearance.
Refer to "Engine / Specifications".
Replace both bearing shells as a set.