Check-up of a vehicle or a machine (5)
I believe the answer is:
'a machine' is the definition.
(I know that motor is a type of machine)
'check-up of a vehicle' is the wordplay.
'check' becomes 'MOT' (MOT check for a vehicle).
'up of' says the letters should be written backwards (I've seen 'upped' mean this (in down clue, made to go up)).
'a vehicle' becomes 'ro' (I am not sure about this - if you are sure you should believe this answer much more).
'ro' written backwards gives 'or'.
'or' is the link.
Can you help me to learn more?
(Other definitions for motor that I've seen before include "(Transport using) engine" , "Car (colloq,)" , "Driver" , "Internal combustion engine" , "Car; powered machine" .)