Motor missing centre, needing to be replaced (6)
I believe the answer is:
engine
'motor' is the definition.
(I know that motor can be written as engine)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for engine that I've seen before include "Machine that converts energy into motion" , "Motive machine" , "search, maybe" , "Mechanical device as source of power, a driver" , "Machine supplying power" .)