Tick of a Clockwork Heart — M.R. Pritchard

Lucas Finnum McKenzie is an unfortunate man on a mission. After the tragic death of his wife during childbirth and the loss of his left arm during an accident, he's left to care for his ill son. Lucas is determined to procure Black Amber, which is intended to power a clockwork heart, the first of its kind that may save his son's life.(A short story at 8,200 words)