Although many modern aftermarket aluminum V8 blocks use iron and steelmain caps without trouble, Chrysler strove for the utmost in dimensionalstability. The cast-iron upper and lower main-bearing caps are designedto keep main-bearing clearance within a range of 0.0005 to 0.0015 forlong bearing life and consistent oil pressure. Specially designed1/2x13-coarse pitch main-bearing bolts thread into the aluminumbulkheads to 50 lb-ft, securely clamping the dual main caps with a7,500-pound screw load. Each upper cap has a roll pin to assist properlocation. If these parts get lost, hang it up and turn your spiffyaluminum block into a coffee table. They're irreplaceable.