Main Bearing Service

Measure outside diameter of main bearing journals in at least four places to determine if out-of-round or tapered. Standard journal out-of-round is .0005" (.013 mm) maximum. Standard journal taper is .0015" (.038 mm). Standard crankshaft journal runout is .0015" (.038 mm).
To check main bearing clearance, position jack under counterweight adjoining bearing being checked so weight of crankshaft will not compress Plastigage and provide incorrect reading.
DO NOT position jack under crankshaft pulley. Crankshaft post damage will result. With all bearing caps (other than one being checked) tight, check clearances using Plastigage method. DO NOT turn crankshaft with Plastigage installed. Main bearing clearance must not exceed .0035" (.089 mm).
NOTE: New bearings are available in standard, .0010", .0020", .010" and .020" undersize for use with standard size crankshaft. Replace upper and lower inserts as a unit. If undersize bearings are used on more than one journal, position in cylinder block.
If standard and undersize bearing combination do not bring bearing clearance within limits, crankshaft must be refinished and undersized bearings installed.
When journals are refinished, chamfer oil holes. Polish journals with No. 320 grit polishing cloth and oil. After chamfer and polish operations, clean crankshaft in solvent and blow out oil passages with compressed air.
Ensure oil distributing grooves on main bearings are installed on same side. Oil new upper bearing and insert plain (unnotched) end between crankshaft and notched side of block. Rotate bearing into place. Ensure main bearing caps are installed with arrows pointing toward front of engine. Install main cap bolts and tighten.