Car repairers replacing casing of engine causes complaint (6)
I believe the answer is:
angina
'complaint' is the definition.
(angina is a kind of health problem)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for angina that I've seen before include "pain in the neck" , "Severe pain from heart disease" , "Painful heart complaint." , "Sharp chest pain caused by heart disease" , "Nag Ian about his disease" .)