Time about right, engine starts up (3)
I believe the answer is:
era
'time' is the definition.
(era is a kind of time)
'about right engine starts up' is the wordplay.
'starts' says to take the initial letters.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
The initial letters of 'about right engine' is 'are'.
'are' written backwards gives 'ERA'.
(Other definitions for era that I've seen before include "Period, age" , "Special time" , "Period of alteration" , "Are involved in time span" , "Long period of history" .)