Weight’s never going over (3)
I believe the answer is:
ton
'weight's' is the definition.
(unit of weight)
'never going over' is the wordplay.
'never' becomes 'not' (I've seen this in another clue).
'going over' shows that the letters should be reversed in order.
'not' backwards is 'TON'.
(Other definitions for ton that I've seen before include "A slang 100mph - heavy" , "Fashionable" , "1000 kilos" , "20cwt" , "Unit of weight equivalent to 20 cwts" .)