Main Bearings

Main bearings are selective fit by manufacturer during production. A standard size bearing may be used in combination with a 0.001" undersize bearing to obtain correct clearance. This combination will decrease clearance 0.0005".
If correct clearance could not be obtained during production, a crankshaft with 0.009" undersize main bearing journals is fitted. A 0.009" or 0.010" bearing may be used to obtain correct clearance.
If engine is fitted with a crankshaft with 0.009" undersize main bearing journals, it will be identified by a "9" stamped in crankshaft counterweight along with large spot of light green paint. The bearing cap will also be painted.
Main bearings may be removed and replaced with crankshaft still installed in engine. Mark or identify main bearing caps to cylinder block before removing caps. Bearings are removed from cylinder block using a bearing removal tool. Install tool in oil hole in crankshaft and rotate crankshaft clockwise.
Crankshaft clearance, taper or out-of-round conditions can be checked using the Plastigage method. If clearance exceeds specifications, a 0.001" or 0.002" undersize bearing may be installed to obtain correct clearance. Both bearings must be replaced on any journal not within specifications.
If correct clearance cannot be obtained or journal tapers or is out-of-round more than 0.001", crankshaft must be removed and ground for undersize bearings. Bearings are available in standard 0.001", 0.002", 0.009", 0.010" and 0.020" undersize.
To install bearings, ensure crankshaft journal and bearing surface in cap and block are clean. Lubricate journal and install bearing cap. If bearings were removed with crankshaft still installed, use bearing removal and installation tool inserted in crankshaft oil hole to install upper bearing. Install main cap noting identification marks and tighten main bearing bolts evenly and to specifications.