Key American gym crew with time clocking mechanism (10)
I believe the answer is:
escapement
'mechanism' is the definition.
(escapement is a kind of mechanism)
'key american gym crew with time clocking' is the wordplay.
I cannot really see how this works, but
'key' could be 'escape' (key on a keyboard) and 'escape' is present in the answer.
'crew' could be 'men' (both can mean a group of workers) and 'men' is located in the answer.
'time' could be 't' (abbreviation) and 't' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for escapement that I've seen before include "Clock or watch mechanism" , "Part of A Clockwork" , "Part of watch mechanism" , "piano piece" , "One-time flight" .)