On 2/25/2019 2:03 PM, Mark J. wrote:
On 2/20/2019 8:26 AM, 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!

Thanks for the information! I have a question, though.

Maybe Shimano hubs are fundamentally different from my
Shutter Precision PV-8 (if I have the model number right).
On my hub, I observe what I assumed was common to all dynamo
hubs: Turning the axle by hand one feels a great deal of
resistance as the hub almost "snaps" from one stator
position to the next, and one feels "push" toward the end of
this transition. So when you spin the wheel in the fork,
the drag and push average out, and the wheel spins quite
freely.

So how do you "feel" the cone adjustment in order to adjust
them? Just barely remove play, and call it good?

I think the SP hubs are cartridge bearings (but I don't
know), so the question is probably moot, like so many things
on RBT.

Mark J.

For the Sturmey GH6 (loose ball) hub, mount the axle in a
vise with adjustable side up. Feel for play at the rim.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971