I guarantee it was cracked at the steam hole,usually the top one and after it cracks from the stress of the head stud and cylinder pressure,then the crack starts to run down the cylinder wall,after taking my 400 apart for the same reason that was what it was,and it cracked on every top steam hole but only 2 cylinders were cracked,and this was a virgin block with only about 30 passes on it,it was maged before it was machined,but thats what I get for using a stock block! went to a bowtie aluminum block as of now hope this one doesn't crack?