98 tracker oil problem

hello i have a 98 16v tracker and recently rebuilt the motor with new pistons rings and everything, it started up ok and run ok and i drove it around the driveway but the next day it started fine but smoked alot so i turned it back off and tried again and it still smoked and the check engine light came on so i turned it back off so i popped the hood and didn't see anything wrong until i got underneth and noticed oil coming out of the exhaust so now im not sure what could be wrong, i used a used head on it that napa said was ok and wasn't cracked but i don't know if it would be that or a ring????