Tractor Repair: 18.5 OHV turning over, but not running, dyt4000, oil release

Question
Hello, I was running my Craftsman 18.5 OHV Intek Plus, @3years old, DYT4000, for about five minutes when a small 2'x3' of white smoke and a small puff sound came from the tractor. It will turn over, but does not continue to run. I do see a "Y shaped" 1.5" crack on the right side of the engine about 6" above the oil release valve and behind the "starter or round cylinder, I dont know what it is" (sorry I don't have the owners manual).  When trying to start it up and it is turning over, the tractor may have a vibrating feel to it, Maybe I am paranoid. I changed the oil, spark plug, but nothing different. Any idea?  Thank you for your time. Also, if I have to get a new engine, would a larger engine fit?

Answer
Hi Jefe
Sorry to say but this sounds very serious .
Your description is very good its the Y crack in the block i do not like the sound of !
Point is do you like messing about with things like this and do you have the ability? you mechanical knowledge seems good
and it is quite possible that a larger motor would fit . take a few measurements and take these down to your suppler.
it may be cheaper to repair the old one. But it will need a complete stripe down.
Martin.