Respect for engineers always comes in (6)
I believe the answer is:
revere
'respect' is the definition.
(revering is a kind of respecting)
'engineers always comes in' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'always' becomes 'ever' ('ever' can be a synonym of 'always').
'comes in' means one lot of letters goes inside another.
're' going around 'ever' is 'REVERE'.
'for' acts as a link.
(Other definitions for revere that I've seen before include "Respect highly" , "night rider to Lexington" , "Hold in great respect" , "Woven fabric" , "Think a lot of" .)