i have a horrible knock in the motor

could be rod knock or a valve could have fallen into the cylinder, either way you are going to need to tear the motor down to find out.

get a statoscope or screw driver and listen to the engine on the valve covers and then under the engine while its running,, just make sure if you use a screwdriver that you put the tip to the engine and the handle to your ear so you don't poke an ear drum out (just thought that I should make that note) the sound should transfer through the screwdriver and be able to locate the sound that way,, rod knock is under the engine and valve train noise be on the top side