I’d like to add one more data point to the “R” casting dates found on some 1921 and 1922 engine blocks. Previous threads discussed the possibility that the R meant that the block was cast at the new River Rouge foundry. Pictured here is an engine block I just got from Dave Huson. The casting date is 8-8-21 and the serial number is 5,298,131, giving it an Aug 20, 1921 production date. The previous discussions had September as the earliest R casting date, although others may very well have surfaced since then. I hope this bit of new data can add more light on the meaning of the R in the casting date.
First I've heard of this Rich. I love stuff like this. Thanks for posting.