Undersize Bearing Selection

Fig. 49 Installing Main Bearing Caps:

Fig. 50 Measuring Main Bearing Clearance:

Two types of main bearings are available, standard and 0.0098 inch (0.25mm) undersize, and each of them has five kinds of bearings differing in tolerance. Each main bearing cap is stamped with a number and an arrow. When installing bearing cap, arrow must point towards crankshaft pulley side, Fig. 49. Check main bearing clearance as follows:
1. Clean bearings and crankshaft main journals using a suitable solvent.
2. Place a piece of gaging plastic the full width of the bearing (parallel to crankshaft) on journal, avoiding oil passage hole.
3. Install bearing cap and tighten cap bolts to specifications. Do not rotate crankshaft while gaging plastic is installed.
4. Remove bearing cap. Using scale on gaging plastic envelope, measure gaging plastic width at its widest point, Fig. 50.
5. If clearance exceeds .0023 inch, replace bearing. Always replace both upper and lower inserts as a unit. A new standard bearing may produce proper clearance, if not, it will be necessary to regrind crankshaft journal for use of 0.0098 inch undersize bearing. After selecting appropriate bearing, recheck clearance.

Undersizes
1. .0098 inch undersize bearing is available in five different thicknesses. To distinguish them, each bearing has a painted identification color on its side. Each color indicates thickness at center of bearing as follows:
a. Green and red, .0835-.0836 inch.
b. Black and red, .0836-.0837 inch.
c. Red, .0837-.0838 inch.
d. Yellow and red, .0838-.0839 inch.
e. Blue and red, .0839-.0840 inch.
2. If crankshaft has to be reground to undersize, regrind journal and select undersize bearing to be used as follows:
a. Regrind journal to obtain a finished diameter a 1.7612-1.7618 inches.
b. Using a suitable micrometer, measure reground journal diameter. Measurement should be made in two directions perpendicular to each other in order to check for out of round condition.

Fig. 55 Undersize Bearing Chart:

c. From journal diameter measured above and letters stamped on cylinder block, select appropriate undersize bearing to be installed referring to Fig. 55.
d. Check bearing clearance with undersize bearing selected.