Sold in the U.S.A. for trail or enduro use, the Alloy Clipper is often mistaken for a Gold Star, but is an export version of the B34 observed trials motorcycle. The allow cylinder and cylinder head are of the small fin style from the earlier ZB model, used to reduce weight. The modest power that this motor produces doesn't require a lot of cooling fins.
The 350 is joined by a 499cc B34 version, which uses a different design of main bearing and a revised crankshaft, but which mirrored the 350's overall ethos.
The front brake size is increased.
The 500 Gold Star is given a new cylinder head at the end of 1951 (designed by Bert Hopwood), and the 350 gets the same treatment part way through the next year. At the same time, BSA make plenty of detail changes to keep the bikes competitive on the track.
A new, duplex cradle, swinging arm frame is introduced, along with an improved gearbox, and the bikes' designations change to BSA BB34.