Stitches up army engineer mates (7)
I believe the answer is:
repairs
'stitches up' is the definition.
(to stitch up is to repair or fix)
'army engineer mates' is the wordplay.
'army engineer' becomes 'RE' (short for Royal Engineer).
'mates' becomes 'pairs' ('pair' can be a synonym of 'mate').
're'+'pairs'='REPAIRS'
(Other definitions for repairs that I've seen before include "Restores" , "Withdraws" , "Doctors" , "Mends, fixes" , "makes good" .)