Despite what has been said, it's a British made 348cc ohv Model CO. Late 1928 or early 1929. If you mail me at peter@triumph.gen.nz with the three letters following the engine number on the crankcase and the frame number (top of headstock viewed from the front) I'll date to the month and send a list of the Triumph booklets I have written as one covers this model. (The 19 booklets written cover all Triumph models from 1902 to 1934, less the 1934 Val Page models, and I'm part way through a series covering the definitive history of Triumph with previously unpublished info and pictures.)
Cheers, Peter (Triumph specialist for the VMCC of Britain)