Using a gasket scraper, remove all traces of gasket material from the engine block, taking care not to nick or gouge the gasket sealing surfaces. Remove the main bearing caps and bridge, separating the bearing inserts from the caps and the engine block, tagging the bearings to indicate their original cylinders, with the oil groove identifying the upper bearings. Remove all threaded oil gallery plugs from the block, which may be very tight and could require drilling out and retapping the holes, using new plugs upon reassembly. If the block is extremely dirty, it should be taken to an automotive machine shop for steam cleaning or tanking. After cleaning, ensure all oil holes and galleries are cleaned again using brushes designed for this purpose, flushing with warm water until clear, drying thoroughly, and wiping machined surfaces with light rust preventive oil, utilizing compressed air if available to expedite drying and clear oil holes and galleries. If the block is not excessively dirty, a thorough cleaning with hot soapy water and a stiff brush is sufficient, ensuring all oil holes and galleries are cleaned, dried completely, and coated with light oil. Clean the threaded holes in the block to ensure accurate torque readings during reassembly by running the proper size tap into each hole to remove rust, corrosion, thread sealant, or sludge, restoring damaged threads, and clearing debris with compressed air if possible. Clean the threads on the head bolts and main bearing cap bolts as well. Reinstall the main bearing caps and tighten the bolts finger tight. Apply non-hardening sealant to the new oil gallery plugs and thread them securely into the holes in the block. If the engine will not be reassembled immediately, cover it with a large plastic trash bag to keep it clean.
