I picked up a junked Vortec 350 and I'm in the process of rebuilding it. The block is hardly worn and everything seems to be in good shape except while magnafluxing the heads I found one crack on each head, both in the same spot.

The red line is where its cracked. It's not a huge crack but I am worried about leaks and the crack spreading to the coolant passage above it.

Am I going to be OK with these because the crack isn't in the chambers or coolant passages? Or am I going to be best off in the long run just buying aftermarket replacements? These are going into a daily driver.

 

Personally, with it being a daily driver, and the area where the crack is, I wouldn't be too concerned with it. You already have them, try it. if a year down the road they begin to leak, then replace them, just costs time and a head gasket.

But IMO I wouldn't be concerned, looks like someone tried to use the wrong bolt, or over tightened to me.

I'm sure someone will disagree, but its all your call whether you wanna save a little money and see if it works, or just spend it and not worry about it

 

I would bring them to a head and block shop. They have seen this before and can tell you if it is ok or not. How far into the head does it run?

I would be concerned that the crack would leak water into that bolt hole and travel up the bolt and into the valve cover

 

I asked my auto shop professor(I'm in college majoring in auto service) and he said that he has seen cracks in similar locations before and that I should be OK because even if coolant leaks up the bolt hole, if the bolt is torqued correctly, it shouldn't be able to make it past the bolt.

I think I'll use them for my budget's sake and hope for the best!

 

"Torquing the bolt correctly" won't stop it from leaking.

However, using some kind of NON-HARDENING sealer (NOT silicone) both on the bolt threads as is necessary anyway, and also under the head of the bolt, WILL stop leaks.

I'd recommend the Loctite/Permatex "automotive thread sealer w Teflon".

 

Sealer, or maybe even a "flat seal" will keep it from leaking past the bolt, sort of like a rubber washer, perhaps? I think you'll be alright. Like you said, for budgets sake