Dishevelled engineers put back more grating (7)
I believe the answer is:
rougher
'more grating' is the definition.
('rough' can be a synonym of 'grating')
'dishevelled engineers put back' is the wordplay.
'dishevelled' becomes 'rough' (rough can mean dishevelled or untidy).
'engineers' becomes 're' (Royal Engineers).
'put back' is a reversal indicator.
're' in reverse letter order is 'er'.
'rough'+'er'='ROUGHER'
(Other definitions for rougher that I've seen before include "Not so gentle" , "less well?" , "Less smooth" .)