The Stovebolt Site Forums The Shop Area Engine Shop 270 GMC 6cylinder head

Are these heads noted for cracking? I have a head that has a cracked that leaked water back into the cylinder which led it to be Hydro locked. The #4 block cylinder will need to be sleaved, but can the head be repaired? When looking into the Exhaust port the crack can be seen. Water will leak into the cylinder and when the exhaust valve opens, water runs into the cylinder.
What the heck happened?

Yes

For some reason air can get trapped in the head when the cooling system is filled. By the time the engine is warm enough to open the thermostat, the head is hot. The incoming rush of water cracks the head.

To prevent this drill a 1/8" or bigger hole in your thermostat to allow air to escape as the system is being filled.

I don't know.