What piston and what motor do I need/have?¿

He truly needs to read this since he still has that front fender on his...Major maiming or death resulting with those fenders.

Funny the only reason why there’s no back fender is because I went a little off road and it bounced into the wheel and screwed it all up. Also chain is tightened. Have to do that on a regular basis. Any clue on the piston though?