I'm looking for advice on AXA HR Traction bottle dynamos and others like it if there are any, as I have seen others on this forum discuss them specifically on other threads. My partner is running it with a clamp on her fork, its alignment with the tyre is as correct as I can possibly make it, but still no matter what I do the screeching/screaming noise when she rides is unreal - especially considering I have read on sales websites that these higher-end bottles are supposedly on the "silent" end of things. I'm not expecting sudden miraculous silence, but given we've tried all kinds of position tweaks and running it both front and back, I'm instead wondering if there's a chance this thing is internally faulty?

Any advice would be appreciated! Thanks.

  • I've not used a bottle dynamo for decades, but i do remember they have a "preferred RPM" Is it possible this one is for a smaller wheel and is tuned for a lower revolution rate, and fitting to a bigger wheel means the dynamo is being overdriven ? Or is the drive wheel slipping on the tyre creating a rubber whine? – Criggie Dec 9 '19 at 11:13
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    Screeching sounds like broken bearings. The usual bottle dynamo sound is more like whining or buzzing. – ojs Dec 9 '19 at 11:27
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    Bottle dynamos need to have the rotor aligned so that the axle points perfectly towards the wheel axle. Also check the unit for any free play. And is the head of the dynamo rubber or metal? – Carel Dec 9 '19 at 20:56
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    @Criggie Since bottle dynamos attach to the tire, which always moves at the same speed relative to the bike as the bike relative to the ground, they don't care what size your tires have. Hub dynamos may be a different story, but bottle dynamos are one-size-fits-all. – cmaster - reinstate monica Dec 13 '19 at 23:51
  • It is true that those dynamos are rather silent when they are not broken. And screeching noise is definitely not to be expected from them. So, I think it's likely you need to get a replacement. If you do, I would not recommend to switch brands: Those AXA dynamos are vastly superior to most other (no-)brands in their resistance to slipping over the tire in the rain. Where other brands pretty much fail with the first bit of moisture, the AXAs can handle pretty much anything but snow sludge. – cmaster - reinstate monica Dec 14 '19 at 0:10

It does indeed sound like your bearings are shot. In some cases a worn bearing (if it's very worn) can cause the stator (non-rotating part of the motor/dynamo) to start rubbing against the rotor (the force the tire exerts on the dynamo pushes the rotor/rotor axle out of alignment causing it to rub against the stator in very bad cases. This would increase the amount of sound more than just a worn bearing.

Note: in some cases a slide bearing/plain bearing/teflon bearing will be used in which case you can't easily service it when it's worn, you could look for replacement parts but it's unlikely they will be available. Bearing type I am referring to can be seen in this image: enter image description here

From what I've read so far there are two types of bottle dynamo design, one where the stator core (soft iron core) is positioned around the rotor such as in this image: enter image description here Disassembly of this type can be seen in this video:

And another type where the winding of the stator and the core are positioned around the rotor, as can be seen in this video:

I am not quite sure what type your AXA HR dynamo is but in practice it doesn't matter much.

They appear to be relatively easy to disassemble judging from the disassembly videos posted above. You could firstly check for play prior to disassembly as suggested by @carel . After disassembling (if there is play/the bearing feels bad) you can take out the bearing, clean the balls/cage(if present), clean the bearing races, apply new/clean grease. And reassemble. You could theoretically replace the bearing but you'd most likely be better off buying a new dynamo when considering the part/labor cost.

I could not easily find bearing replacements specifically for the HR Traction but if you measure the ball diameter you can find those ball bearings seperately and replace them, but do keep in mind the bearing races will probably also be worn and these are in general non replaceable parts. So you will most likely not get it as good as new by replacing only the balls. Tool used for measuring ball bearing balls: enter image description here You can also use a caliper or micrometer if that's all you have.

What you could perhaps also try is to loosen the nut that secures the cap of the dynamo a bit, if that is over tightened than I believe your bearing will also be too tight (just as a headset bearing can be too tight and will cause the bearing to not run smooth at all). Try loosening it a bit and see if it runs more smoothly/quietly afterwards.

Also make sure to clean the dynamo properly, even though sand/grid getting under the cap or even in the dynamo is quite unlikely, it could be considered a cause of excess noise depending on how the bike is used (in muddy conditions I could imagine sand getting under the dynamo cap).

In my experience it is quite normal for bottle dynamos to make some noise, you will definitely know when they are engaged due to the sound they produce. So they won't be fully silent, for that you'd need a hub dynamo.

There are many alternatives to axa HR bottle dynamos, they are quite common in the Netherlands: here are a few: https://www.internet-bikes.com/zoeken/11506779-11506787/?search=dynamo

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    The stator design in the AXA dynamos is quite different (the magnet is a rotating cup that grabs around the entire stator assembly), but from my experience, they are quite a bit harder to take apart than the bottle dynamos in the videos. I don't recall whether I managed to take mine apart without destroying it. It was already broken anyways, so I didn't care. I only did it to get a look inside... – cmaster - reinstate monica Dec 14 '19 at 0:02
  • @cmaster could you briefly explain the method you used for disassembly? Do you remember which type of bearing was used? – Maarten -Monica for president Dec 16 '19 at 1:22
  • Sorry, no. I was most interested in rotor/stator design and didn't really pay much attention to the bearings. And I certainly didn't pay enough attention to know how to take it apart without destroying it. – cmaster - reinstate monica Dec 16 '19 at 7:04

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