Boss with old motor for heavy metal fan (10)
I believe the answer is:
headbanger
'heavy metal fan' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'boss with old motor' is the wordplay.
'boss' becomes 'head' (synonyms).
'with old motor' becomes 'banger' (I can't explain this - if you can you should give a lot more credence to this answer).
'head'+'banger'='HEADBANGER'
'for' is the link.
Can you help me to learn more?
(Other definitions for headbanger that I've seen before include "Heavy-metal rock fan" , "crazy individual" , "Old music lover" .)