1929 BSA Sloper, 500cc OHV, Model S29
One of the best-known Vintage BSAs, whose forward-sloping engine started something of a trend in the design of big singles for several years. This is a twin-port model (though the other exhaust pipe and silencer are hardly visible) - also a popular design feature in late vintage and pre-war machines. Like most of these, the Sloper did not have twin exhaust valves, and the twin-port design was largely cosmetic.
Not to be confused with the Panther - P&M, makers of this range, used a sloping engine on many models, sometimes replacing the frame's front down-tube, almost throughout their existence, right up to the Sixties. Most other sloping-engine designs, including this BSA, retained a conventional frame, the angle of the cylinder being intended to reduce the overall height, as well as looking more sporting.