My friend has a 1986 3.0L chevy block which is cracked right below the exuast manifold and he runs the boat regularly. He put JB weld over the crack and it doesn't leak water. My question is, is it ok to run a block like this if the block is not leaking? I thought a block was pretty much junk if it is cracked. He thinks he can run it without replacing it for a long time. Is this true?? Anyone else ever run a motor with a cracked block?