Plead to exchange bicycle part (5)
I believe the answer is:
pedal
'bicycle part' is the definition.
(I know that bicycle has part or parts pedal)
'plead to exchange' is the wordplay.
'to exchange' is an anagram indicator.
'plead' is an anagram of 'PEDAL'.
(Other definitions for pedal that I've seen before include "cause a revolution in cycling?" , "One of two a cyclist needs" , "Foot-operated lever" , "Lever operated by foot" , "related to feet" .)