A project at Netley Marsh
Every year we travel to the Netley Marsh Eurojumble to hunt for spares. In 2015 this motorcycle was offered by a French seller. It looked like an interesting BSA M23 Empire Star project with a good JM23 engine, but the later WD M20 frame made it appear to be a collection of parts.
Closer inspection showed that, apart from the frame, the other major parts were genuine Empire Star. The motorcycle remained unsold. After meeting the seller again at Beaulieu, we agreed to buy it if the crankcases matched and were undamaged. The engine checked out and the deal was done.
The top of the M range
Introduced in 1937, the M23 Empire Star sat at the top of the M-model range. It was a specially tuned development of the M22, with a high-compression piston, higher inlet cam and larger carburettor. It came with a 20-inch front wheel, fresh-looking “Empire Star Green” paint and a gold star on the tank panels.
The period drawing shows a single-port head. A two-port head with upswept pipes on both sides was also a popular option. The aluminium rocker box and large 289 carburettor are among the details that make this engine so distinctive.
Original paint uncovered
The J prefix on the engine number indicates 1938. We removed rust and several later layers of paint from the petrol tank with paint stripper. The later paint dissolved quickly; beneath it was a thin but remarkably tough layer of the original “Empire Star Green”. The tank is now back in its surviving original colour. The oil tank received the same treatment and revealed chrome beneath the paint.
Finding the right frame
The later War Department M20 frame is dimensionally similar to a 1938 M23 frame but differs in important details, particularly the oil-tank mounting. The 1937–38 machines used a plain rectangular oil tank carried by two projecting strips on the front frame. Later machines used a larger tank wrapped further around the rear mudguard and mounted to a square plate behind the front frame.
The WD frame was sold and, with help from contacts, we found an HM20 frame. It is a 1937 frame, but apart from the number it matches the 1938 pattern. The cycle parts were fitted and the engine rebuilt. The motorcycle now looks substantially complete, though considerable work remains. It is being kept together while other projects take priority.
