typhoon 172 i think engine rebuild is needed:(,

right couldnt get my typhoon started the other day and have checked everything, it has lost compression but engine turns over very freely. checked the reeds, carb and spark and all three are okay. i really hope i dont have to rebuild it, iv only had it a few days and sounded so crisp. any common problem im missing here? i was just riding to the shop normally when it happend, i thought i ran out of fuel but it didnt start again, no noises at all before it died just sounded normal. not really sure what to do but if i have to rebuild im putting a 54mm top racing crank in this b*tch

 

anyone?