Velocivixen

I'm so excited to have received this. The Gentleman Cyclist sold me one of his prototypes and it just arrived. Now I can get into that GH6 and clean it more. The hub has been overhauled but there is a lot of grit between the armature and magnet that I couldn't get to.


Magnet Keeper for Sturmey Archer Dynohub by velocivixen, on Flickr

3speedslow

Great ! Jon is a great guy and has lots of nice stuff to help us with these 3 speed steeds. Let us know how well it works.

RobbieTunes

So, is that what a chick magnet looks like?

jimmuller 

You could things besides magnets in that. Paper clips, loose change, car keys. Stuff like that.

3speedslow

Is this circular wonder on his site yet?

Velocivixen

No. I emailed and asked when & how much. He offered me this one - one of his prototypes for a modest sum plus shipping.

Magnet Keeper in Place by velocivixen, on Flickr
SA Dynohub Armature "Before" by velocivixen, on Flickr

SA Dynohub Armature "After" by velocivixen, on Flickr

I used a brass bristle brush on a Dremel around the outside. There's this sort of cellophane orange plastic paper between the wires and the metal.

Mr. VV has one of those meters and I set it on AC 200 and while spinning the wheel touched the two tips to the two posts to see if there's electricity. I have no idea how to use the thing or what it means. There are lots of high numbers on the screen, which eventually end up at -1 upon stopping.

gna

I asked Jon about magnet keepers, and he said someone had been in contact with him. I guessed it was you.

Our STO did say he was thinking of another run of keepers, so email him if you're interested. It may tip the balance.

steelbikeguy

just out of curiosity... does the magnet keeper fit into the gap between the magnet and the armature, so it is in place before the armature is removed?

The gap between the magnet and armature should, ideally, be very small, so that portion of the keeper would need to be even thinner.

I don't have a dynohub, but have a couple of Schmidt hub dynamos and have designed headlights to work with them (this is what bike riding electrical engineers do for fun), so I've been curious about the legendary Dynohubs.

Steve in Peoria

jyl

I'd love it if you'd do a post on how you rebuild those dynohubs, someday. I would be really interested to see that.

Also, after you get it fixed up, I'm curious how what the output turns out to be. Sounds like you have a VOM instrument, so you can measure voltage and amperage while spinning the wheel.

mountaindave 

Velocivixen

@gna - he said that getting them into production has "been a headache". He was very quick to offer me one. I thought it was sweet.

So does that mean I have "magnetism" now?
@steelbikeguy - you hold the magnet/armature in your left hand with the terminals towards your palm, then the part of the keeper you see with a recessed shelf goes against the armature, and as you push the keeper, the armature & magnet separate and the keeper essentially slides the armature out and takes its place.

What at surprises me is the amount of rust that has reformed from when I overhauled it about 10 days ago. What's to keep it from getting rusty again? How will that affect the output of energy?

rhm

WD40 should prevent rust nicely.

I just overhauled a GH6 the other day. They are really robust hubs; for all the hand wringing I've read on the internet (on this forum, in fact) about demagnetized magnets, I've never encountered one. What I have encountered, however, is stripped axles. The whole axle will be fine, except for 2 mm where the cone locknut sits; that part is stripped, so the cone locknut just spins.

Fortunately the axle is a common thread, 10 mm x 26tpi. Cheap freewheel hubs often have solid axles this size; if you want to go hi-tech, you can even use a QR axle.

I also have a MKII dynohub from the 1930's, which puts out 12v. The design is the same as a GH6, but the proportions are different; the MKII is a lot bigger. To remove the dynamo unit, like the GH6, you unscrew the little nuts from four thin bolts, and the whole dynamo should drop out. Well, mine doesn't drop out, and I haven't figured out any way to get enough purchase on the thing to pull it out with force. I doubt a lot of force will be needed, but I can't apply any, not even a little. Very frustrating. In lieu of a complete overhaul I have dripped oil into it (there's an oil hole in the shell) and massaged grease through the gap by the cone, hoping it will find its way to the bearings... but an overhaul is still needed.

JohnDThompson 

You place the keeper on the magnet/armature assembly and use it to push the armature off the magnet. As the armature slides out, the keeper slides in.

steelbikeguy

I took a look at the instructions on Sheldon's pages to see how the dynohub comes apart, and learned that the bolts that retain the magnet are removed first, allowing the magnet to come out with the armature. That clarifies things quite a bit!

At that point, I'm assuming, is when the magnet is slid off of the armature and onto the keeper. Makes sense.

@Velocivixen : as far as treating the rust on the steel poles of the armature... the best approach would be to remove the poles from the winding, but can that even be done? I'll let the others here suggest rust treatments. My only caution would be to avoid using anything that might attach the varnish insulation on the dynamo's wiring.

Steve in Peoria

Velocivixen

Unfortunately I stripped either the bolt or the nut of one of the 4 bolts that holds the magnet/armature to the hub. When I out it together before I screwed nut too tight. I did this once before and found a round headed bolt the correct size & length and filed a flat spot on its head to sit properly. I think I messed up the threads on the bolt.

I wouldn't call myself ham fisted but I messed up on this one. This'll call for a trip to the hardware store.

Superbe69

Ok call me crazy but I just rebuilt my Dynohub and used a $6.00 part that I bought at the hardware store to solve the keeper problem. In fact there's a good chance you might have one sitting in your own garages.
Ready for it!! A Two and three quarter inch (2 3/4") round wire brush which you would normally attach to a drill for removing heavy rust or paint. The metal body clears the magnet with room to spare and the bristles (being wider due to the conical shape) infill the magnet with a tight fit that actually caused a couple of sparks as they slid in. I had the magnet out for at least 45 minutes while I service the armature and rebuilt the bearings. Voltage readings after were actually improved. Probably just from cleaning everything. The rim spins very nicely with that slight tug caused by the magnetic force.
Hope this helps, but make sure you buy the 2 3/4" brush, NOT the 3" one, that could crack your magnet (IMHO) since even the 2 3/4" one was pretty snug. Good Luck, Superbe69

clubman 

I think dialectic grease would keep the rust down for awhile. It's meant to pass electric current.