It turns up as a machine part (3)
I believe the answer is:
cam
This clue might be a double definition.
'it turns up as a machine' is the first definition.
The definition suggests a singular noun which matches the answer.
'part' is the second definition.
(I have seen 'Part of engine' mean 'cam' so perhaps 'part' could also mean 'cam')
Can you help me to learn more?
(Other definitions for cam that I've seen before include "Projection on a rotating shaft in contact with another part" , "running into Great Ouse?" , "Runner" , "River also called Granta" , "East Anglian river" .)