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SA AG Dyno Hub Servicing

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SA AG Dyno Hub Servicing

Old 10-18-22, 12:52 PM
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Andrew R Stewart 
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SA AG Dyno Hub Servicing

I am the wrench for some guy's rebuilding of an English 3 spd. The SA AG Dyno Hub is dated 1953. He asked me to overhaul the hubs then lace up both wheels w/ new rims and spokes. I'm quite comfy working on AWs but it's been close to 40 years since I last did one of the rear Dyno Hubs and I don't remember if I took it completely apart or just did a flush and lube. I looked through my Sutherlands manuals (yes, I have a few including the separate coaster, internal hub one) and Sheldon Brown's site but don't see an answer to my question.

Can I pull the axle with the rest of the guts (as the kids that come into the shop say) and leave the armature within the magnets?

I see all kinds of warnings to not separate the armature from the magnets but no mention if one has to tap the magnets out of the hub shell to access the gear internals. I know my options if I can't pull the internals. Andy
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Old 10-18-22, 01:27 PM
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Please don't rely entirely on this, but if memory serves, the warning about separating the armature from the magnet relates to long term storage, not short intervals when servicing.

Generally magnets need to be stored with a "keeper" to maintain their field properly. In this case the armature is the keeper, so removing it long term will weaken the magnet. So, my advice is to replace the armature into the magnet if your service gets interrupted waiting for parts or whatever. Otherwise, proceed normally.

BTW- the magnets are pretty brittle, so EXTREME care is needed if you decide to remove it.
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Old 10-19-22, 07:21 AM
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1960 Sturmey shop manual with AG section:

Sturmey-Archer Heritage :: History

Download the PDF. Bob's your uncle.

Sturmey sez: "Separation, even for a fraction of a second, will cause loss of magnetism."
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Old 10-19-22, 07:49 AM
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Sturmey-Archer did offer a "keeper ring" to protect the magnets when servicing the hub. It's just a simple steel ring sized to fit closely to the magnets:
Attached Images
File Type: jpg
keeper.jpg (61.0 KB, 8 views)
File Type: jpg
keeper-ring.jpg (46.9 KB, 8 views)
File Type: jpg
Keeper_Ring_spec.jpg (46.5 KB, 10 views)
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Old 10-19-22, 09:56 AM
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tcs- I have spent hours looking at this book a long long time ago. It is what helped develop my love of SA hubs. The shop where I first took apart SA hubs had this book on its shelves for reference (back when we turned pages instead of the clicking on an arrow). The text is pretty much what is also shown by the Sheldon Brown site. So, unfortunately no new info for answering my question.

All- I've decided that I will not take the magnet/armature out of the shell and only remove what I can otherwise for cleaning. The gears seem to work well and the bearing surfaces I can see are in good shape, so I don't think there will be any parts needs. I will talk to the guy about this approach before going ahead. Thanks for the help. Andy
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Old 10-19-22, 03:21 PM
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Here's what the hub looks like after the solvent cleaning. The axle is left in the shell, it won't come out w/o doing a magnet removal, which I am avoiding. These will air dry for a few days and I'll reassemble with strategically placed grease and OEM oil. Note I have zip tied the parts that I need to keep in the right order and locations.

What's not seen are the replacement rims (original Raleigh R23.0 EA-3, used but in nice shape), the front hub, spokes and spoke elbow washers. These hubs have a very thin flange (close to half what's common these days).and modern spoke elbows are longer then back in the day. The washers will place the crotch of the elbow against the flange, about 5 washers for each spoke. (Unless I find a source for old NIB spokes with their shorter elbows). Andy
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Old 10-23-22, 02:53 PM
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Originally Posted by Andrew R Stewart
Here's what the hub looks like after the solvent cleaning.
Was there an image?
As for the magnets losing their strength, unless the magnets are really of inferior quality I doubt that brief periods without the armature would do any harm. A piece of iron pipe of a suitable diameter could be used as a keeper.
I re-built a "Joule" (first generation) dynohub and had the armature out for a few hours at a time while working on the bearings. Between sessions I left the armature ("stator", more correctly) in the hub shell. No loss of function was apparent. The magnets in this case were of the "ceramic" type, so perhaps their maintenance requirements were different.
Some possibly relevant discussion HERE.

EDIT: Some even *more* relevant discussion HERE, ranging from keeper "analogues" to actual keepers.

Last edited by sweeks; 10-23-22 at 04:21 PM.
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Old 10-23-22, 05:47 PM
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Sorry to forget to attach the shot... I'll check out the linked discussions, thanks.

I was able to buy some "old world" spokes with short elbows. Tomorrow I'll try cutting and threading one down in the hope that that will go well. The elbow/flange fit is far better than with modern elbow sizes. Andy
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