Remove any remaining gasket material from the cylinder block with a spatula, being careful not to damage the surface.
Remove the main bearing caps and remove the bearings from the cylinder block and caps. Sign which cylinder the bearing belongs to, as well as the part from which it was removed (from the cover or cylinder block); put them apart.
Using special hex wrenches, unscrew and remove all threaded plugs of the cylinder block channels.
If the engine is heavily soiled, it should be taken to a workshop for washing with a strong steam jet or in a hot chamber. Almost all stores sell brushes for cleaning oil channels and holes. Flush the internal passages with a stream of warm water until the water runs clear, then dry the cylinder block thoroughly and lubricate the treated surfaces with oil to prevent corrosion. If possible, blow compressed air through the block and internal channels to speed up the drying process.
If the block is slightly dirty, it is enough to wash it with a stiff brush and warm water and detergent. Take your time and do this job carefully. Regardless of the flushing method, thoroughly clean the oil channels and holes, dry the block and lubricate the treated surfaces with oil.
The threaded holes in the cylinder block should be cleaned with a tap to ensure correct torque readings during reassembly. Cleaning with a tap will clean the threaded holes from dirt, traces of corrosion and sealant residues, and restore the thread. If possible, blow out holes with compressed air to remove material residue after tap cleaning. Thoroughly clean the threads of the cylinder head bolts and main bearing caps.
Reinstall the main bearing caps and finger-tighten the bolts.
Install new plugs in the cylinder block, after lubricating them with high-temperature sealant. Make sure that the plugs fit correctly and that there are no distortions, otherwise leaks may occur. To fit the plugs, you will need a special tool. This operation can be performed with the same level of quality with a hammer and a mandrel, the diameter of which corresponds to the opening of the plug.
If the engine is not being assembled at the moment, cover the cylinder block with a plastic cover to protect it from contamination.