BSA 1939 M23 Silver Star 500cc 1 cyl ohv 2509



BSA   1939   M 23  Two-port  Silver Star 496 cc OHV    frame #KM 23.380 engine #  KM23.329

Responsible for the 1937 range of BSA machines was brilliant engineer Val Page. 
He reshaped the complicated system of machine types that had become confusingly diverse over the years. 
The 150 cc machine was dropped and all 250 cc and 350 cc models were catalogued  in the “B” group, while all the other singles  above 350 cc came into the “M” group. 
The V-twins formed the third group. So now the whole range was divided into only three groups. 
That is to say, the  750 cc  v-twin was labeled the Y 13 and the 1000cc twin the G 14 and to make sure it would not become too transparent for the customers there was one  350 cc model that fell in the “M” group, the   350 cc OHV De Luxe M 19. 
Page replaced the forged backbone frame system with a fully brazed-up frame with one top tube. 
The crankcase sump was discontinued, the magdyno became rearward-mounted again and  the valve gear enclosure was improved in such a way that for the first time there was a complete coverage for the whole of the overhead gear. 
The cylinders were air-hardened to reduce wear.   For model year  1939 there were 3 models in the 500 cc ohv class that all had a four speed foot controlled gearbox. 
The M 22  was meant for both solo and sidecar work,  the M 23  Silver Star was a sports machine  with specially tuned engine and  the M 24 Gold Star was the ultimate sportsman’s dream. 
All three had   bore/stroke dimensions of 82×94 mm.  
This M 23 is equipped with the optional two port cylinder head  and high level exhausts. 
The machine has been restored some years ago  and is a good runner.