Gear change on BSA B31 B series Gear box

[Richard Hinton]

Anyone know about BSA B31 gear boxes. (B series) Problem cant change gear. Disconnected link from selector and identified problem is with selector assembly. Springs are ok nothing seems out of place or broke. But cant change gear when all connected

[Swarfcut]

 I'm thinking this is the B & M box  fitted to Rigid and Plunger models, as the usual box on B Models on S/A bikes is well covered on the Forum, being the standard gearbox type across A & B S/A Models' Ranges. 
 
Mention of a link to the selector mechanism reflects this, the two designs are entirely different.

     This earlier box is a masterpiece of belt and braces design and far too  complicated for the job it does.  Removal of the gear control plunger cap, spring and plunger should allow the selector shaft to rotate easily. This shaft is geared to the control quadrant, so wear or damaged teeth here can cause problems. Other thing to check is freedom of movement on the upper and lower ratchet pawls and associated components assembled  onto what Drags call the gear change operating plate. On a long standing box, I reckon simple seizure of the  selector mechanism is  inevitable with the complexity of design. Selector forks move along the selector shaft as it rotates, as is now more common Japanese practice, so binding here will also prevent gear selection. Service Sheet 608 covers this box.

 Swarfy

[scotty]

Assuming its a swing arm model
BSA Service sheet 311 can be helpful

[Richard Hinton]

Thanks for info ill look into this and see but make take time as rebuilding A10 Engine at present. always something with these old timers.