Bearing race wear or bent axle (in Dynamo hub)?

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natmat
Posts: 245
Joined: 8 Jan 2007, 2:25pm
Location: Sherborne, Dorset

Bearing race wear or bent axle (in Dynamo hub)?

Postby natmat » 2 May 2016, 9:57am

Hello all,

Problem: when the axle is rotated there is obvious grating/grinding at the same position each revolution.

The hub is a Shimano DH-s501 Alfine front dynamo and the grinding (above the normal dynamo notch-resitance) is once per revolution. This makes me think the bearing races (either the captive in the hub and/or the screw-down upper race) are worn, or the axle is bent. Would anyone agree?

If the it were ball bearing wear, then I would expect the grating to occur at any position, which isn't the case.

I've looked at the races on both sides of the hub (oddly all Shimano tech pages shown only the race on the non-electrical side) and can't see anything obvious. I've replaced balls on non-electric side with 3/16" SS (no change) and am going to to the other side today (I don't expect it'll make any difference).

There is mixed opinion about this hub online based on some comments about early failures. I'm thinking it's beyond economic repair (would be close to £50 in parts for races and axle I've had thought, that's if the parts are actually available).

Any thoughts before I ditch it and build up a new dynamo wheel?

Ta, Nathan.

Brucey
Posts: 37278
Joined: 4 Jan 2012, 6:25pm

Re: Bearing race wear or bent axle (in Dynamo hub)?

Postby Brucey » 2 May 2016, 10:33am

I think it is very likely that the rubbing sound is being caused by a slightly eccentric magnet/hubshell assy (which is quite normal) and some corrosion on the stator. If water gets into the hub then the stator will corrode and this will eventually cause rubbing/grating sounds. It is of course quite possible that the bearings are also worn (which can add to the rubbing); the water gets into the hub via the bearings and the grease that shimano use is 'not at all corrosions resistant' in the context of UK winter weather.

I'd suggest that you may be able to cure the problems you have by

a) unscrewing the centre from the hub, cleaning the rust from it
b) overhauling the RH bearing (careful with that wire!)
c) using something to corrosion-proof the stator
d) use decent waterproof grease in the bearings.

NB to remove the stator on this hub you need (IIRC) a full octagon wrench. It looks like a headset wrench will work; I can tell you that it almost certainly won't, not on a well used (and internally corroded) hub. The reason for this is that you may need at least 100ftlbs to release the centre, and a headset wrench won't manage that on an aluminium octagon, because it is mainly driving on just two flats, not eight.

The other wrinkle it is as well to be aware of is that (like many shimano front hubs) it is possible to get the ball bearings trapped between the edge of the cone and the edge of the cup; this can knacker everything in double-quick time. If you have just one good cone, I'd suggest that you stick it in the RH side; you can change the LH cone at your leisure, as it were.

BTW if you do decide to ditch the hub do let me know by PM; I could do with one of these for spare parts.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

User avatar
natmat
Posts: 245
Joined: 8 Jan 2007, 2:25pm
Location: Sherborne, Dorset

Re: Bearing race wear or bent axle (in Dynamo hub)?

Postby natmat » 2 May 2016, 12:37pm

Hi Brucey,

Thank you for your detailed reply. I hadn't thought of internal rust being an issue because the exterior looks in such good condition and there's no trace inside the races. Ball bearings are now removed from both sides, so I'll tackle the final disassembly soon. I have the correct socket for the stator, so fingers crossed once out it will reveal the source of the rubbing noise. The rhythmical rubbing noise is annoying, but also there's a noticeable braking effect on a hand-spun wheel, which can't do my avg mph any favours either.

I'll report back what I find.

Brucey
Posts: 37278
Joined: 4 Jan 2012, 6:25pm

Re: Bearing race wear or bent axle (in Dynamo hub)?

Postby Brucey » 7 Jul 2016, 8:20am

how did you get on?

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~