Do my bit and take mine on the chin (5,2)
I believe the answer is:
pitch in
'do my bit and' is the definition.
I can't judge whether this definition defines the answer.
'mine on the chin' is the wordplay.
'mine' becomes 'pit' (as in a mining pit).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'pit'+'chin'='PITCH-IN'
'take' is the link.
Can you help me to learn more?
(Other definitions for pitch in that I've seen before include "Set to work" , "Eat heartily - help with some task - contribute money" , "play one's part" , "Lend a hand" , "Get to work" .)