What causes this to happen?
 

Attachment 2718



That thing skyrocketed right through the hood.

I looked into this one, and I think the actual answer is that it broke. The engine block split between the mains and the head, leaving the deck and cylinder bores attached to the head. The head, of course, launched. Either it had a sh*t-ton of blow-by sending fuel down the cylinder walls and the crankcase exploded, or it overboosted bigly, or something like that generated a lot of pressure in the inside of the engine. Then, of course, it cartwheeled out of the tractor.

These tractor pull diesels run crazy high cylinder pressures. Sometimes all it takes is a small casting flaw in the block.