Changed gear after clutch casing damage (6)
I believe the answer is:
charge
'damage' is the definition.
(I've seen this before)
'changed gear after clutch casing' is the wordplay.
'changed' indicates anagramming the letters.
'after' is a charade indicator (letters next to each other).
'casing' suggests removing the centre (the outside letters are the case of the word).
'clutch' with its centre taken out is 'ch'.
'gear' with letters rearranged gives 'arge'.
'arge' after 'ch' is 'CHARGE'.
(Other definitions for charge that I've seen before include "money to be paid" , "Price for a service" , "impeachment" , "Rush forward - cost" , "person in custody" .)