traders

hey guys. i got a 81 SR250 exciter the guy i bought it from did a makeshift job of fixing his cam shaft problem by just slaping a screw to keep the cam sprocket in place. and i learned the hardway about this cuz that lil screw flew off anyways was wondering if anyone know of a larger engine that'll fit into this frame i really like the bike but since this happened i have a choice of fixing it or slapping something bigger in. if anyone has any info lemme know thanx mike