wondering what would have caused this

[Rawze]

You said someone replaced the head. If they were lazy and used a high-speed wire wheel on an air-grinder to clean the top of the block with the liners in place, this could have caused an issue like this. I have seen it once before. Power tools should NOT be used to clean the top of an engine block for just this reason. It only takes 0.001 - 0.002" (you cannot see this small amount) of scratching to the top edge of a liner before a problem like this will start to set in. High combustion temps will drill a hole through and widen the problem after that.

I would have first suspected this as the problem, but when you look at the pictures more closely ...

There is a clear sign of a stress-crack in the head in the valve seat at #3. It looks like there was a stress-crack in the head from the very beginning of when it was installed. Although it is now washed out by combustion gases, You can see it on the left in the picture, and how deep it was.

Where was the head purchased?

Does it have a warranty?

And was it a used/reman from a local shop machine/ head re-man shop? -- Very bad decision, NEVER re-use an ISX head if it is more than 400k miles old!, EVEN IF YOU HAVE IT RE-WORKED BY A GOOD MACHINE SHOP!! - 4 out of 5 will fail a thorough magma-flux for reasons just like this.

Those would be my first questions, because someone somewhere owes you for an entire engine now because of a bad head. -- It looks pretty clear to me that the stress crack in the head at the edge of the valve caused this.


LOOK on the drivers side of the head near the rear of it. You will find out the date of manufacture and if it was a cummins re-man or not. If it is a cummins re-man it will have an RX in the part number stamped on it. As well, if the date on the head is old (more than 3-4 months before it was replaced), it is a good bet that it WAS NOT NEW OR A CERTIFIED RE-MAN!



I am also with gearhead on this one. It is highly likely your engine block is etched and destroyed between the cylinders. Putting it back together with new head and liners could turn out to be a very risky and expensive failure. - Not worth the risk.