Choppers bearing large mechanical parts (5)
I believe the answer is:
axles
'mechanical parts' is the definition.
'choppers bearing large' is the wordplay.
'choppers' becomes 'axes' (I've seen this before).
'bearing' is an insertion indicator.
'large' becomes 'l'.
'axes' enclosing 'l' is 'AXLES'.
(Other definitions for axles that I've seen before include "Shaft on which wheels rotate" , "Shafts of wheels" , "Wheel rods" , "They may be involved in turning" , "Wheel shafts" .)