If the casting had a poured bearing before, it had to be scraped (machined) to eliminate most of the adhered old bearing. The casting was heated with the remainder of the mold in place to accept the new pour, (600 degrees doesn't bother aluminum or steel) so the old bearing material would mix with the new. The top of the mold had at least two holes, a larger tapering one to accept the new pour, and another one or two small ones to let the air vent. The extra material as a bump in the inlet and air vents were cut away. Then the bearing were scraped to the proper diameter.