Small motor -- a black Beetle (6)
I believe the answer is:
scarab
'beetle' is the definition.
(scarab is a kind of beetle)
'small motor a black' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'motor' becomes 'car' (informal term for car).
'black' becomes 'b' (abbreviation as in pencil classifications).
's'+'car'+'a'+'b'='SCARAB'
(Other definitions for scarab that I've seen before include "Beetle regarded as divine by ancient Egyptians" , "Holy beetle" , "Large dung beetle" , "Large dark beetle" , "Type of beetle" .)