All the pictures in this string ( especially post 84 )with broken cast cranks and even a few I have looked at on line I think show a common failure point.
I see the cracks starting internally at the intersection of the main and rod oil passages where there are a lot of sharp edges that naturally can not be got to and rolled over to help lessen the chances of a crack starting.
These sharp edges must look just like what’s found in the main journals of the block where the oil feed holes meet up.
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I do stuff for reasons.
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