On Wednesday, February 20, 2019 at 8:26:57 AM UTC-8, Tanguy Ortolo wrote:
Hello again,

I have finished repairing my front hub dynamo, that was making a
cracking or clicking noise, and that eventually started to produce a
high drag against wheel rotation.

That hub dynamo is a Shimano DH-3N31, and I was able to open its ball
bearings with no issue. In particular, without breaking the phase wire!

The right (drive and power output side) bearing locknut was loose, which
allowed the corresponding cone to become loose as well, which I think
was the cause of the noise, and at some point to tighten itself, causing
the later drag.

I noticed the right side of the dynamo was distorted, with part of it
pushed inside by a bit less than one millimetre. I suppose I must once
have caught something between the fork and the hub, that would have
applied a pressure against the dynamo and moved the locknut, causing all
this trouble. Now, since the dynamo is still working correctly, I think
I will use it for a while and monitor it closely before replacing it.
These things are not really cheap, especially when you buy them with a
prebuilt wheel.

I cleaned the ball bearings, greased them and replaced the balls. The
left-side ones were clearly damaged, but not broken, and the right-side
ones seem intact, but I replaced them nevertheless.

One thing to notice with the dynamo hub, compared to a regular hub, is
that you cannot remove the axle after just removing the locknuts and
cones on either side, or even on both. This is because the dynamo stator
is installed on the axle, and it is caught inside the rotor and hub,
that forms a cage around it. There is some play though, and when
adjusting the cones back, you have to make sure you are in the middle of
that play, otherwise you could be forcing the dynamo stator against the
side of its cage. The point of contact are supposed to be the balls, and
nothing else!

Now that I have adjusted the cones and locknuts again, it seems to work
just fine. Thanks for all the advice!

--
Tanguy

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