Cracked piston in fresh engine

it just cracked down to the top ring and that was it. I could of sore I had the ring gap right i just checked it and it was a lil big thou should of been .032 and it was .039 on this one ring but that was what i was thinkin the problem was also. This was the first time i tried file to fit rings. Expensive learing experience huh!!! Just when the ridin' got fun! I imagin that would explain the light smoke i would get every now and then untill it started smokin all the time. Any suggestions for a first time filer?