Main Bearings: Notes

NOTE: When removing crankshaft from engines equipped with automatic transmission, mark torque converter and drive plate for installation reference.

Support crankshaft at counterweight adjacent to main bearing being checked. Ensure that all bearing caps other than one being checked are tight. Starting with rear main bearing cap and working forward, remove one cap at a time and check bearing clearances using Plastigage method.
If clearances are not within specifications, undersize bearings may be used to achieve select fit. A standard bearing may be used in combination with an undersize bearing to obtain specified clearance. Do not combine bearings that differ beyond one bearing size as a pair.
Remove all upper bearings by inserting fabricated cotter pin in oil hole of crankshaft journal and rotating crankshaft clockwise to roll bearing from engine. See Fig 1.

Fig 1: Upper Main Bearing Remover/Installer Fabricated from a 7/64" cotter pin. Courtesy of American Motors/Jeep Corp.
If clearance exceeds specification using a pair of .002" (.0051 mm) undersize bearing inserts, measure crankshaft journal diameter with micrometer. If journal diameter is correct, crankshaft bore in cylinder block may be misaligned, which requires cylinder block replacement or machining to true bore.
If diameter for journals No. 1 through No. 5 is less than 2.4981" (63.452 mm), or diameter for journal No. 6 is less than 2.4975" (63.437 mm), replace crankshaft or grind down to accept appropriate undersize bearing insert.
To install, oil new bearing and rotate crankshaft so upper bearing will rotate in direction of locating tang. Install bearing cap and tighten bolts to specification.