Machine part broken by large blockage (4)
I believe the answer is:
clog
'blockage' is the definition.
(I've seen this in another clue)
'machine part broken by large' is the wordplay.
'machine part' becomes 'cog' (I've seen this in another clue).
'broken by' is an insertion indicator (inserted letters break into the word).
'large' becomes 'L' (eg in clothes sizes).
'cog' placed around 'l' is 'CLOG'.
(Other definitions for clog that I've seen before include "Become blocked with wooden-soled shoe" , "Block up - type of shoe" , "Shoe with a thick wooden sole" , "Dutch shoe" , "Block; sabot" .)