Under the laws of all states in this country, since you are a minor, you can cancel the contract for the motorcycle that you purchased and get a refund of all paid for it less fair rental value. The law holds that minors cannot enter into a legally valid contract.If you can have the mechanic write something up for you that the motorcycle was in very poor shape when you got it, even better.Under the laws of all states in this country, the seller of an item must disclose all material aspects of the item affecting price paid or desirability for a potential buyer. Failure to do so is concealment. From what you have written, it appears the the seller concealed the fact from you that the engine needs to be rebuilt on the motorcycle from you. If so, you have another basis to cancel (rescind) the purchase of the motorcycle.