Block Strength

A rod is usually bent under hydro lock not broken, but it could break it. What makes you think it was hydro lock. Even if a cylinder wasn't firing it wouldn't hydro lock from the fuel. The only motors I have seen that hydro lock from fuel while running are blown fuel and alcohol motors or a mechanical injection motor that isn't "backed down" before starting. Without a pic or seeing the block it is difficult to tell. Could have been just a rod failure.

Chuck