question about topend and piston

[2001warr]

hey uys I have a few questions on the topend of this warrior. this is my first 4stroke and its all kinda new to me. what causes the middle piston ring to break, and I mean when I got the jug off about an 1in of the ring was gone. this thing was smoking like my old 250r why I am tearing it down. the cylinder is smooth as a babys butt so I am assuming that it will need some work also. should I take the head and have the valves checked as well. I need some help here guys. im on a very limited budget thanks