1987 supra

i have a 1987 supra non turbo i only but the car for 200.00 cuz my cousin was going to collage an that all i had at the time i have had for 2 yr an just start working on it it has a knocking noise coming form the top of the engine an i cant find out what it is i even go to a automotive skool and they r haveing trouble to have any guess an it is in good confition..