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Sturmey’s right-hand ball rings: are you losing the thread?

20/02/2015
Some instructions for disassembling Sturmey-Archer gears include a mysterious statement such as this:
“Next, unscrew the right-hand ball ring but because it has a two-start thread and must be replaced in its original position, that position must be marked. String or adhesive tape may be attached to the spoke nearest to the letters ‘SA’ which are stamped in one of the notches on the ring.” (From the 1956 Master Catalogue, sub-section 4, page 15, paragraph 1.)
The reason for replacing the right-hand ball ring in the same position is as follows. If the ring is screwed back in the alternative position, 180 degrees out from its original position, there could be some slight distortion of the completed assembly, due to a very slight difference of alignment between the hub shell and the ball ring. Whilst not noticeable at the hub end, it can result in the rim being slightly out of true. (The longer the spokes, the more the discrepancy is amplified.) So the precaution is in order to avoid the possible need to re-true the wheel.
This matter is not well documented but the rare 1992 Sutherland’s Handbook of Coaster Brakes and Internally Geared Hubs makes the point clearly. To facilitate correct re-assembly, Sutherland’s advises marking the ball ring at the point nearest the lubricator, rather than attaching tape or string to a spoke.
The reason for the two-start thread is to facilitate screwing the ball ring in relatively quickly, while having a stronger mechanical connection than an equally fast single-start thread would offer. For a given screw pitch, a two-start thread will screw in twice as fast as a single-start thread.
Tony
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From → Cycling, Gears

11 Comments
  1. jsallen1 permalink

    Sutherland’s Handbook of Coas ter Brakes and Internally-Geared hubs is much easier to find than one might think. It is online! http://www.sheldonbrown.com/sutherland.html .

    • Hi John,
      Yes, I very recently discovered that good news myself – well done. I doubt there are more than a handful of hard copies in the UK. I had to import mine via a British cycle company that exhibited in the USA.
      Tony

  2. Remo A. Peter permalink

    Does this advice still apply to the new, Taiwan-made hubs?

    • I’m not sure, Peter, but I have sent a request to Sturmey-Archer for clarification. I’ll let you know when I get their response.
      Cheers,
      Tony

  3. bruce permalink

    if you lose track of what you are doing, I have a good trick to get you back on track.

    Simply try the ball-ring both ways round in the hubshell, and finger tighten each time. Whichever way the ring goes on furthest is the ‘correct way’ (i.e. same way as originally).

    If it goes on both ways exactly the same (which I have never seen) then it is that rare thing, a ‘perfect’ twin start thread.

    New parts are manufactured and assembled as if they are perfect but the threads in the hubshell are permanently deformed the first time they are fully tightened and the hub is ridden on.

    You will usually find that a new (or replacement used) ball ring will also go on better one way than the other if fitted to a used shell.

    In any event I think this is of more importance with aluminium than steel hubshells.

    I note also that the twin start thread

    a) makes cross-threading much less likely and

    b) makes the ball-ring breakaway torque (during removal) substantially less than it would be with a single start thread. I think that this is the real reason it is used. With a single-start thread in use, removing the ball-ring would be much like removing a screw-on freewheel, i.e. regularly necessitating torque values in the region of 200ftlbs.

    cheers

    • Many thanks for these very interesting comments, Bruce – much appreciated.
      Tony

  4. Dave Connley permalink

    What happens if you for any reason need to replace the ball ring with a new spare one ? How could you possibly know which way to screw in the new one. Many years ago I had a guided tour around the Sturmey Archer factory courtesy of the then manager Nick Sanders ( not the Nick Sanders of television fame). I saw that many of the parts were cold forged under huge pressure. The screw thread would have been machined on after the forging process and would possibly not run perfectly true to the bearing surfaces. I have dismantled and re assembled dozens of hubs over the years and never had a problem but can see that if you have a ball ring that is slightly out of true it will throw the rim out slightly if you screw it in on the opposite thread. As for it making any difference to the operation of the hub you have nothing to worry about. If it was that important then Sturmey Archer would have marked both the ball ring and the hub shell with markings for correct assembly.

  5. Don Kingston permalink

    Thanks, that is what I will be doing this morning after work.
    Many Thanks
    Don

  6. Don Kingston permalink

    To this story, is there another way to tell this mistake has been made? I had made 2 white dots with permanent marker for my reference and then after cleaning and during reassembly I noticed my white marks were gone. I guess I cleaned very well. This is my first time trying this and would like to notice if my 50-50 chance went against me before I cause permenent damage.
    Thank You for these articles and the sharing of knowledge.
    Don

    • Hi Don,
      You shouldn’t end up damaging the internals, even if the ball-ring is 180 degrees out. Just re-install the wheel in the bike and, if the rim is still true, you should be OK. If not, you either need to disassemble the hub and re-insert the ball-ring turned 180 degrees relative to the shell; or, leave the hub as it is and retrue the wheel by adjusting the spokes. The former course of action would usually be less hassle.
      Tony

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