|The only photograph of a Dynohub keeper ring I could find on the internet|
Update: just after posting this I found a wealth of information on the keeper ring in this thread on bike forums, including dimensions and part number!
Other than infrequently turning up on eBay, they are unavailable. Gentleman Cyclist does, however, mention on their parts page that they will soon have keeper rings for the Dynohub (you should take a look at the other interesting bits and bobs they carry for the 3-speed enthusiast).
Well, I had an old Dynohub from '75 that was rusty as all heck. It came from a trashed ladies Raleigh Superbe that was languishing in the basement of Polly's Recycle in the east end. The armature could barely spin within the ring magnet and the whole assembly was covered in a coat of rusty grit. Usually a Dynohub can be serviced without the need for removing the armature from the ring magnet, but in this particular hub's case, the armature need a good going over with a wire brush. So, I had my Internet Material Synthesizer make one out of mild steel #45. Now, I think my Dynohub magnet upgrade makes the original magnet kind of obsolete, but I was getting a bunch of other parts made so I thought I'd get a keeper ring made as well. It arrived today:
|Machined Dynohub Keeper Ring|
It has a 2.700" outer diameter, the same as the armature, and is 0.75" thick.
|Dynohub Alnico ring magnet with armature. Don't remove that magnet without a keeper!|
|Dynohub ring magnet with keeper|
Does it work? I don't know. I pushed the armature out with the keeper, so the field wasn't disrupted. The magnet feels about as strong as it did before the armature was removed. The design is very similar to the original, so I expect it's doing its job.
Do you want one? I can easily get more made. They would cost between $15-$30 each, depending on number I get made in one go. I'm also thinking of offering a magnet upgrade for the Dynohub (this is still a work in progress though...)
If you're interested send me an email (find the address in my profile).