Engine Builders: The AERA Technical Committee offers the following information regarding additional crankshaft bearing undersizes for 1967-2005 GM Chevrolet V8 engines. This information refers to Chevrolet engines that are also designated as “Big Block” and “Small Block” engines.
To allow engine builders increased flexibility to select fit engine bearings for desired oil clearance during assembly, additional sizes are now offered by one aftermarket bearing supplier. These new undersize bearings became available after requests from Chevrolet high performance engine builders and apply only to their “Performance Bearings,” see Chart 1.
These new sizes give engine builders the ability to select fit bearings on a .010″ or .020″ reground crankshaft. If clearance adjustments need to be made, use either an extra clearance part for more clearance, or an undersize part for less clearance. Select fit bearings have been available for standard size crankshafts, but until now, engine builders were limited to only the .010″ or .020″ bearings if the crankshaft was reground. If the desired clearance was not obtained, they had to make clearance adjustments by machining additional components.
According to the bearing manufacturer, it is permissible to mix sizes if less than .001″ adjustment in clearance is desired. When mixing sizes for select fitting, never mix parts having more than .0005″ difference in wall size, and always install the thickest wall shell in the upper position if installing a rod bearing, or the lower position if installing a main bearing. Part numbering is similar to previous undersizes as explained here.
The last digit of the part number indicates the bearing size, i.e. -9 indicates .009″ and -11 indicates .011″. According to the manufacturer, additional fit information can be found in the “installation and fitting tips” listed in their current catalog.
New Bearing Undersize Part Numbers