Wiktionary
n. (context idiomatic English) One who talks incessantly; a chatty or loquacious person.
Usage examples of "motor mouth".
Monitoring lobby traffic was the troublemaker's troublemaker, Pisshole Pat, the chain-smoking desk clerk with the crippled arm and the motor mouth, who, from the security of his bulletproof glass cage, enjoyed harassing peers and innocents alike, his bleached eyes a reproach to naive hipsters like Perry who cultivated his tolerance out of the same dark need pushing them out to the margins here, all the good little girls and boys, lives from the womb pointed like compass needles in this damned direction, the tug of The Life, you think you're on a visit when you've really found a home.
If that had been me, I would have called Motor Mouth to attention and really eaten his ass out.
She had to be careful she didn't turn into a motor mouth when she was answering her calls.
Without hesitation Rojer took it, and knew that the chief had liked him for himself, and because he'd put a plug in that motor mouth of an ensign.