Revolving part going left or right (5)
I believe the answer is:
rotor
'revolving part' is the definition.
(I've seen this in another clue)
'going left or right' is the wordplay.
'going left' says the letters should be written in reverse (letters written right to left).
'right' becomes 'tor' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'or' written backwards gives 'ro'.
'ro'+'tor'='ROTOR'
Can you help me to learn more?
(Other definitions for rotor that I've seen before include "one lifting chopper?" , "Mechanical turning part" , "Turning component" , "Part of, eg, a motor" , "Device to propel a helicopter" .)