I have a 1955 B31 with a 4 speed gearbox. Reassuringly, the case is stamped 'std'. I would like to replace the gear cluster with a 5 speed touring set. I note that Nova Racing supply these, marketed for the Gold Star singles. With the exception of the needle roller bearings, are the gear casings basically the same for these machines? I tried sending a message to Nova Racing and received a rather non-committal reply. I am a competent machinist and have access to full workshop facilities so minor changes, bearings and bushes are no problem.
Thanks
SimonH
I have a Nova 5-speed box on my bitsa (ABSAF 600 engine).
Excellent choice and works really well.
The cluster fits neatly. Mine went into modded standard case. The drive side closed layshaft needle roller drops straight in.
Timing side needs line boring to accommodate the open needle roller. I can give you the bsa and Torrington codes later.
Only issues I had were the selector forks were slightly under size internally they had to be opened up.
The layshaft thrust washer had to be surface ground to get correct 10 thou end float.
You need to open out the inner end cover to allow the new selector fork.
Also spec which shift pattern you want related to rear set or std footrests (I wanted up for up and down for down in rear set position.