Green’s Dictionary of Slang

1. unsound, second-rate.

1970

A. Sillitoe Start in Life (1979) 78: My cronky old car wasn’t exactly the high-powered javelin I’d supposed it to be at first.

2. (Aus./US Und., also cronkey) corrupt, dishonest, lying.

1935		A.J. Pollock Und. Speaks 27/2: Cronky, wrong; no account.
1963–74		B. Humphries Barry McKenzie [comic strip] in Complete Barry McKenzie (1988) 69: I only came down here yesterday, you cronky tart.
1987		J.D. Macdonald Dress Her In Indigo 160: Without the beard he had the con look, the loser look. [...] He had the cronkey look, that flavor of upcoming trouble that alerts any cop anywhere.