Refuelling operation? Mine's best! (3,4)
I believe the answer is:
pit stop
'refuelling operation?' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'mine's best' is the wordplay.
'mine's' becomes 'pit's' (as in a mining pit).
'best' becomes 'top' (top can mean the very best).
'pits'+'top'='PIT STOP'
Can you help me to learn more?
(Other definitions for pit stop that I've seen before include "Break during motor race" , "Break for fuel etc." , "brief service" , "GP changing time" , "Pause for refuelling etc during race" .)