Why do Flathead V8 Blocks Crack?

[Dobie Gillis]

Originally Posted by Admiral

This has been my experience as well. The late-run blocks seem to have more cracking issues than earlier examples; casting quality also appears a little rougher, with far more flash and core wire hanging around.

I know this thread is pretty long in the tooth but it piqued my interest (too much time on my hands?) I agree with Admiral about the late-run castings. I had a '53 block repaired and the guy said as he was drilling it for pinning he was hitting hard and soft spots in the cracked area (exh. valve seat to cylinder). This indicates to me that the alloy wasn't well homogenized before it was poured. The hard and soft spots set up stress areas due to differential expansion. Stress will relieve itself given an opportunity such as overheating. I believe the foundry did a slipshod job of mixing the alloy. Not on all of them, mind you, but on enough of them to give the late blocks a reputation.