Turn over motor, even losing velocity (6)
I believe the answer is:
careen
'turn over' is the definition.
(thesaurus)
'motor even losing velocity' is the wordplay.
'motor' becomes 'car' (informal term for car).
'losing' is a deletion indicator.
'velocity' becomes 'v'.
'even' with 'v' taken away is 'een'.
'car'+'een'='CAREEN'
(Other definitions for careen that I've seen before include "Turn" , "Tilt to one side" , "List, heel over to one side" .)