The TW24 is a pretty rare model; basically a 2 3/4 h.p. (350cc) Isle of Man model. It differs from its big brother the RA by having a sloping top tube frame, and carrying its oil in a compartment in the petrol tank rather than in an alloy reservoir under the motor. The TW cylinders are the same casting as the RA, but have 57mm bore (68mm for the RA). The cylinder heads are also externally identical, but the combustion chambers are machined to match the smaller bore. The rest of the motor/gearbox is identical to the RA.
The crank cases I'm using are numbered IE/1B 41. The table in Appendix 2 of "The Best Twin" lists prefix IE as "2 3/4 h.p. 1923 T.T. engine ohv, 57 x 68mm, 350cc". IE/1B is listed as "2 3/4 h.p. Williams Bros., Sydney City Council". Williams Bros. were the Sydney agent for Douglas, and were involved in racing in the major centres in Australia. I suspect "Sydney City Council" is a red herring: although the Council bought quite a few Douglases for various mundane tasks, I doubt they had much need of T.T. engines!
Numbers-wise, the cases are ideal: certainly 2 3/4h.p., a matched pair (match number A89 on each half) and delivered to the Australian agent Williams Bros. Condition-wise, there were none of the usual exit wounds, but they were a bit ratty where corrosion had ravaged the timing side. The front right engine mount was totally gone, rear right pretty tatty, the face of the timing chest was rotted, as was the face of the gear change lug - rotted right through in fact. On the drive side, the only corrosion was in the thin part of the case that covers the cam bearing, which was cracked and peeling.
The cases are now back in good order. The corroded parts have been machined off and new metal added where necessary for structural reasons (thanks Wolf and Seb - masters of the mill). Non-structural repairs use aluminium-filled epoxy and lots of hand finishing. Welding may have been possible, but given the rarity of the surviving metal I decided not to risk it.
The photos below are probably self explanatory: as acquired, on the mill, and the (almost) finished product.
Cam and followers next.
Leon