Machine part chap must regularly handle (8)
I believe the answer is:
camshaft
'machine part' is the definition.
'chap must regularly handle' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'handle' becomes 'haft' (haft is a kind of handle**).
'chap'+'must'='chapmust'
The alternating letters of 'chapmust' are 'cams'.
'cams'+'haft'='CAMSHAFT'
(Other definitions for camshaft that I've seen before include "driving force" , "Car part" , "Rod to operate valves in an engine" , "Internal combustion engine valve controller" , "Fat chasm (anag) - internal-combustion engine part" .)