Precisely rotates favourite component in engine (6)
I believe the answer is:
tappet
But I can't explain it at all! Could you help me understand?
(Other definitions for tappet that I've seen before include "Lever to transmit motion from one part to another, in car engine say" , "Moving part in an internal combustion engine" , "Motion transmitter in a machine" , "Apt pet for valve operator" , "piece of mechanism" .)