The 1938 BSA M24 Gold Star

1938 BSA Catalogue illustration (Nov 1937)

The first production Gold Stars differed in certain minor details from the prototype illustrated in the BSA catalogue for 1938. To overcome oil leakage problems, the cylinder head and barrel castings were altered to incorporate two additional cylinder head fixing bolts on either side of the push rod tunnel, and the rocker box was recast with two additional mounting bosses, again to overcome oil leaks. An Amal 10TT36 Carburettor was fitted in place of the standard Amal type 89. The silencer on the production bikes had a separate tail pipe, so that the overall length of the exhaust could be adjusted for optimum performance. 

By kind permission of Mortons media Group Ltd

Following the arrival at BSA in 1936 of Val Page, the new range of motorcycles for 1937 revealed a significant redesign of the single cylinder engines, with the adoption of dry sump lubrication. The all new M20 500cc side-valve engine, and the M19, M22 & M23 OHV engines as pictured above, were to form the
   basis for all larger capacity BSA single cylinder engines until the final 500cc Gold Star in 1962.
Based very closely on the 500cc M23 Empire Star, first produced for 1937, and pictured above, the 1938 production model Gold Star shared most of the older model’s cycle parts, except the frame, which was constructed of lighter Reynolds 531 high-tensile tubing, the petrol tank, which was unique to the Gold Star in having an integral tool box in the top, in place of the instrument panel, and the rear brake drum which sported thin fins around its diameter. The ammeter and light switch were housed in a panel in the headlamp shell. The other main visible differences were the all-alloy engine with built-in pushrod tunnel, the TT carburettor, and the “Elektron” gearbox cases. The M24 also had a small tubular oil pressure indicator mounted above the timing case in place of an indicator button in the tank top instrument panel of the M23. The first production M24s , bearing Engine and Frame numbers starting at 101 and prefixed JM24, were built  in November/December 1937, and  the first batch of 10 were dispatched on 17th December.
Production of 1938 Gold Stars continued until the autumn of 1938, when the factory switched to production of the new 1939 model. The last one, engine JM24 365, in frame JM24 404, was despatched on 6th July 1939 to the British Army for the 1939 ISDT.  
A total of approximately 266 1938 JM24 bikes were built, and of these, 85 were despatched to destinations outside the UK.

1938 JM24 Gold Star