I let a person test drive a motorcycle, and not the engine is about to blow up, as if he road it really hard on his drive. Can i file a lawsuit against him?
First, because you gave this permission to drive your motorcycle, he normally would not be responsible for a mechanical problem that has developed. The only alternative you have is to prove that he somehow abused the cycle while riding it. Unless you have a witness to this or an expert report from a motorcycle mechanic, you don't have much of a case.