engine cratered

I suddenly had very little compression in cyl 4 and 6 on my 5.7L Vortec.
Pulled the heads and discovered gasket gone between cylinders 4 and 6. Upon closer inspection I discovered that the cylinder head and engine block ( both cast iron) had a channell about a 1/4 inch wide and about a little over a 1/8 inch deep between them. Obviously the heads and block are now junk. What I am trying to figure out is what caused this? The engine has never been abused, overheated and only has about 30,000KM on it.
Any ideas or anybody seen this also?

I suddenly had very little compression in cyl 4 and 6 on my 5.7L Vortec.
Pulled the heads and discovered gasket gone between cylinders 4 and 6. Upon closer inspection I discovered that the cylinder head and engine block ( both cast iron) had a channell about a 1/4 inch wide and about a little over a 1/8 inch deep between them. Obviously the heads and block are now junk. What I am trying to figure out is what caused this? The engine has never been abused, overheated and only has about 30,000KM on it.
Any ideas or anybody seen this also?I have but one question ,why would you tear it down.30,000 km on 2005 .I was thinking warranty,but likely void now unless you are a GM tech at a GM garage. Sorry not trying to be smart ,just curious. hopefully it`s in something older

I have but one question ,why would you tear it down.30,000 km on 2005 .I was thinking warranty,but likely void now unless you are a GM tech at a GM garage. Sorry not trying to be smart ,just curious. hopefully it`s in something older

If it's a 5.7, it's no newer than a 98.

ah ok thanks I just looked at his profile and seen `05 and thought that was the unit it was in with only 30,000 km on it .

A head gasket failure can cause this. Common causes of head gasket failure on SBC Gen I and Gen II engines are neglected coolant, heavy loading before the engine is fully warmed and stabilized, or improper installation. Head gaskets on the older SBCs usually don't just happen by themselves - At least not like they seem to occur on later engines.

Any failure of the head gasket, whether due to coolant or compression leakage, can cascade into a block deck and/or head deck erosion condition if ignored. It sounds like you've learned that already.

The block and head may not be scrap. Although replacement blocks and heads are very available and relatively inexpensive, it is possible to repair the damaged surfaces by welding into the area with a high nickel content filler material. The nickel alloys very well with the iron substrate, and makes for an actually stronger repair area. Of course, some machining would be required to bring the surfaces back to a true and flat condition, but you're going to be removing the engine if you replace it anyway. If the weldor is skilled, the amount of filler material can be controlled enough so that the block deck surface may be able to be trued while the block is still in the vehicle.

Forget about using any epoxy fillers or sealants. Those would only be a temporary repair at best, and you'll be right back there repairing it properly within months.

Can you provide a photo of the damaged surfaces? Seeing the extent of the erosion may help determine whether it is repairable.

I have seen this happen to 3 or 4 400 M ford engines. All were the same year and in the same model truck being used in similar manor. I think it can happen to any engine that blows a head gasket as you have described, for any of the reasons that Blue Bowtie listed. I agree that the block can be repaired without being removed.

Thanks,
I'll try and post pics.
Compression test was done just 3 months prior with all good. Engine started missing slightly all of a sudden and was only driven for a few miles back home where it was discovered compression close to nil and the resulting tear down.
And yes its an older truck, but with very low mileage on a new crate engine.