RE: ST G20 15D
Old cast iron that has not been used or in a stressfull application has been normalised by nature , its been through many daytime heating and nightime cooling cycles. This reduces the internal stress's and heals microcracking from the casting process - this makes it desirable for engine use, provideing the cast iron is of suitable quality in the first place. A tidbit of history, Roll's Royce discovered that engine blocks,crankshaft and piston castings that were left outside in the weather for a year or more befor machineing produced more reliable engines, this was one of there secrets to success in there early days.