3 speed dynohub sprocket

[robsa]

Hi , on last leg of restoring a 1948 rudge sports only ive got a problem, the rear sprocket on the dynohub is worn out and I want to swap it for a larger one anyway.
Now , when ive done them before its just been a case of popping a circlip off and bobs your uncle.
But, this one is threaded and I haven't a clue-
A- how do I take it off
B- what do I swap it with
If any of you knowledgeable people can give me any pointers id be very grateful.
Ive tried local lbs but no joy except from one in Newark with a lovely old lass in who reeled off the spec and code and said she could do it.

 

[MichaelW2]

Usually they are Sturmey Archer 3-spline, fixed with a snap ring/circlip.
They come in 1/8 or 3/32 chain width and some have dished offset for setting appropriate chainline

 

[raleighnut]

Hi , on last leg of restoring a 1948 rudge sports only ive got a problem, the rear sprocket on the dynohub is worn out and I want to swap it for a larger one anyway.
Now , when ive done them before its just been a case of popping a circlip off and bobs your uncle.
But, this one is threaded and I haven't a clue-
A- how do I take it off
B- what do I swap it with
If any of you knowledgeable people can give me any pointers id be very grateful.
Ive tried local lbs but no joy except from one in Newark with a lovely old lass in who reeled off the spec and code and said she could do it.

John at Bob Warners in Leicester could do it (He's about 10 minutes walk from Leicester train station) I wouldn't be surprised if he had one in stock.

 

[tyred]

Sturmey's prior to c1951 were threaded sprocket before the circlip fitting came into service. To the best of my knowledge, this is just a standard track sprocket so easy to source. It will definitely screw on, although be careful as a dished sprocket may be required to get the chainline right. You will see what your's looks like when it's off.

The difficult part is getting the old one off. You will need to dismantle the hub and clamp the driver in the vice and unscrew with a chainwhip. It will be tight. Very tight! Or what I did with mine was replace the driver with the later circlip variety which I did as I had Sturmey spares lying around and had a good sprocket to fit in the tight size.

Either way you need to dismantle the hub. The important thing is to never separate the magnet and iron rotor within the dynamo part if you expect the dynamo to work.

If you do replace the driver with the later circlip model, don't dump the old threaded driver as they will accept a threaded freewheel block which gives the possibility to build a hybrid with many gears and it's worth a few quid even if you don't want to go down this road yourself.

 

[tyred]

This is what you find when you dismantle it -

Rudge Roadster Sturmey Archer AG Hub by braveheart1979, on Flickr

You need to hold that piece which the sprocket is screwed on to in a vice and unscrew with a chainwhip.