Green’s Dictionary of Slang

(UK Und.) to take the works of one watch and place them in the case of another with the aim of disguising its origins.

1847		G.M.W. Reynolds Mysteries of London III 66/1: Tim sent the yack to church and christen.
1857		‘Ducange Anglicus’ Vulgar Tongue 38: [Specimen of Flash] Bill had flimped a yack [...] He sent the yack to church [Translation] Bill had hustled a person and obtained a watch [...] The watch he sent to have the works taken out and put into another case.
1860		Hotten Dict. of Modern Sl. etc. (2nd edn).
1869		J. Greenwood Seven Curses of London 87: To take the works from one watch, and case them in another – churching Jack.
1873		Sl. Dict.
1882		Sydney Sl. Dict. (2 edn) 10: I got the thimble to church and fenced it for three cooter, and four deaners [...] I got the works of the watch changed to another case and sold it for three sovereigns and two shillings.
1895		Crowe Aus. Sl. Dict. 98: ‘[T]o church a yack,’ to christen a yack, i.e., to take the watch out of its case or change the number.
1901		Argus (Melbourne) 20 Sept. 6/4: The watch is otherwise known as a yack [...] Should [a criminal] deem it advisable to remove the works from one case to another he is churching a yack.
1909		J. Ware Passing Eng. of the Victorian Era.
1935		A.J. Pollock Und. Speaks 21/2: Churching yaks, removing precious stones from settings of stolen jewelry or movements from watches.
1935		(ref. to 19C) R.T. Hopkins Life and Death at the Old Bailey 63: The following crook’s words and phrases date from the days of the old Old Bailey: [...] to put the works of a watch out of one case into another – to church a Jack.