the cylinder started getting water in the hole. I could not find any problem on the gasket. But, there is a groove that will hang your fingernail between a headbolt and the cylinder bore. I think the wire-ring for the head gasket would not be able to seal across this groove/crack. I was thinking about trying jb weld but it was soo cold yesterday it would not flow very well.

Worst case, I have to pull it back apart to weld the crack

 

Sorry, you need a new block. There's no fixing this problem.

 

Hmm.. why could not crack not be welded and the block decked?

It might be more trouble that it's worth but considering it is a pretty fresh 400, I don't think it is SOL.

 

Sounds like you don;t really have anything to lose by trying the JB Weld, except some of your time... it works sometimes depending on the details...

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"So many Mustangs, so little time..."

 

think i'd use dye pen or mag on it and make sure i had a crack before i jumped in making any repairs. if you're going to fix it i'd vee it out and weld it with nickel and have it machined.

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-=ICON MOTORSPORTS=-
1st & 3rd

 

If it really is a crack, something that wasn't there when the engine was last put together, then it goes into the headbolt threads. Just fixing the surface isn't going to help any, since it'll crack again when you torque the head back on.

Not sure what you mean by a "fresh 400": Fresh 400 block? Fresh rebuild? Either way, it was probably a flawed, or possibly abused, casting.

It might bear evaluation by a knowledgeable shop, but it doesn't sound good based on your description.