400 block number 1 cylinder thin area.

I have sonic checked many 400 blocks and even blocks with bores mostly at >.180 thickness have scarey/thin spots.

That said most of the cracked cylinders I have seen, including my own, began to crack parallel to the deck at the top of the cylinder on the thrust side. Eventually the crack takes a path down the cylinder making it an "L" shape.

Stab a Dorton sleeve in it and it should be fine