There is no apparent need to replace the crank. Your friend probably tried to screw the pedal in the wrong direction and perhaps that is what is going on with your attempt with the new pedal. Also as mentioned the pedals come in two sizes; 1/2" for one piece cranks like yours and 9/16" for the rest (make sure you bought the correct size).I assume you bought a pair of pedals to replace the one with the messed up threads. If you look on the threaded end of the pedal you will see an "R" or an "L" stamped on the spindle next to the threads (sometimes there is just an L) depending on which pedal you are looking at; these stand for Left and Right as you would be sitting on the seat. The right side has a standard thread and the left is reverse. If the threads in the crank are messed up a bike shop hopefully will have an 1/2" reverse tap to chase the threads.
Last edited by onespeedbiker; 08-26-12 at 09:33 PM.