A test piece of work in car construction (5)
I believe the answer is:
motor
'work in car construction' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'a test piece of' is the wordplay.
I cannot really understand how this works, but
'test' could be 'mot' (MOT test) and 'mot' is present in the answer.
'piece' could be 'r' (abbreviation for Rook) and 'r' is found in the answer.
'of' could be 'o' and 'o' is found in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for motor that I've seen before include "Machine that converts energy into motion" , "Driver" , "Travel by car, engine" , "Engine - relating to movement" , "go quickly" .)