Green’s Dictionary of Slang

cog-wheel n.

SE in slang uses

In phrases

have cog-wheels (v.)

(Aus.) to be demented.

1919		W.H. Downing Digger Dialects 17: cog-wheels — ‘To have cog-wheels’ — to be demented.
1924		(con. WWI) A.G. Pretty Gloss. of Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: cog-wheels. ‘To have cog-wheels’ to be demented.