Overhauling a Shimano DH-3N71 Dynamo Hub

[yello]

Evening all. First post from a lurker/browser but I thought I'd share this knowledge.

My bike had developed a front wheel noise. It was definitely the wheel/spokes/hub. I checked spoke tensions and they were good. So I decided that I had to pull the dynohub apart, despite Shimano's advice being that it was NOT serviceable. I searched and found the following...

Trinity Bicycles

...using those instructions, I carefully pulled the hub apart and found the drive side bearings were shot. A set of 22 new ball bearings set me back a massive €1.60 and the entire job took maybe an hour. That was it - job done!

As I was fearing the possibility of having to buy a new hub, I am indeed a happy fellow! 

[border-rider]

Blimey, that's a useful post

Received wisdom has always been that these are not user-serviceable.

Thanks !

[Simon Galgut]

Been there, done that. It's fine if you only do it a couple of times, but you will break the wire eventually (especially if you are ham fisted), so only do it when absolutely neccessary.

[rogerzilla]

That's useful - I assume a DH-3N80 is the same.

The RH cone looks just like one from a Sturmey-Archer AW, which is reassuring - those intersecting labyrinth seals are completely resistant to water ingress except by total immersion.

[yello]

but you will break the wire eventually

Yes, I suspect you're right. It's a solid copper wire so it'll only take a certain amount of bending before breaking.   

So, if you're going to do this job, be very careful when pulling the hub apart. You will have to bend the wire in both disassembly and assembly but try to keep it to a minimum. 

[Andrew]

You are right! It's broken, after 15000km and the 2nd set of bearings.  1st change was at 3000km.

To be fair, I think I just got unlucky as others report much better mileage than that. It's not put me off Shimano either and I'll replace with the DH-3N80.

Oh, btw, if anyone wants the document linked to it the 1st post (the link is now dead) then pm me.

[rogerzilla]

I think I've b0rked mine after only 1,000 miles by loaded touring.  It generates electricity OK but something is broken; there's a horrible creak from the front of the bike with each wheel revolution, getting worse when braking or leaning forward on the bars.

[clarion]

Shame that link seems no longer operative

[andrew_s]

the words are on the web archives, but not the pictures.

[iddu]

Shame that link seems no longer operative

clicky

[SNIPPED #1]
If only life was that simple, the wheel is a s/h purchase and I think the lock nuts and cones have been played around with.

Why is it difficult to take #6 apart ?

The problem is this wire that runs from the rotor along the axle to the light connector:

This wire is thick but not very flexible and therefore breaks somewhat easily. In order to take #6 apart and assemble again you have to manipulate this wire several times. This alone can break it. Also, when unscrewing or screwing on the left cone/lock nut there is a danger that they grab hold of the insulation and either pull the wire apart or strips off the insulation which again will create a short circuit so the light won't work.

It is therefore a good idea to now exactly where the left cone/lock nut should be placed on the axle when assembling the #6 part again to avoid any unnecessary danger to the wire by turning the cone back and forth. So make sure that the wire is pressed down in the trench and clean the trench if necessary.

According to Shimano #6 isn't serviceable but is replaced as a whole unit, so no official spare parts can be had. It is however very likely, that the left cone hidden inside #6 is identical to the right cone (#15).

[SNIPPED #2]

Here is a quote from the original Trinity bicycle guide for overhauling Shimano dynamo hubs:

"Place your 15mm cone wrench on the drive side cone in between the plug and the hub body. Place your 17mm wrench on the locknut. Using your finger to prevent the plug assembly from turning, break the lock nut from the cone and remove the locknut. The plug assembly will try to turn with the locknut, but if you allow it to rotate while the axle is stationary, the wire which runs from the internal assembly to the plug will break and your hub will be ruined."

When you have disassembled the "internal assembly part" (rotor) try to minimize any manipulation of the wire to the absolute necessary; it will break if you bend it too many times.

[SNIPPED #3]

Get a good feeling for how the wheel rotate when the cup and cones are
adjusted correct before taking it apart. The magnets makes normal cup-
and-cone feeling of preload difficult.

Measure dish on the wheel first, make sure it is centered. Take
accurate measurements of the distance between the end of the axle and
lock nuts. This is to avoid any unnecessary fiddling with the rotor
side lock nut and cone when assembling the rotor part again, since
this risks breaking the rotorwire. Place the lock nut and cone right
the first time when assembling the rotor.

Document exactly how you take the rotor apart with a digital camera.
Again the reason is that the wire seems only to be able to take that
many bendings before it brakes, so avoid too much fiddling, but
reassemble it correctly the first time.

You don't need any special tools, but a lancet and a pick will be
handy.

You take the cone off on the rotor side by screwing it off the axle,
but since the rotorwire runs along a trench /slot in the axle, the
cone may grab hold of the rotorwire and rip it apart when the taking
the cone off. So be careful that the rotorwire doesn't  protrude above
the slot. Perhaps use a lancet to clean off the gum that Shimano seems
to use to glue the wire to the trench with, but avoid cutting in the
wire insulation.

There seems to be good reason to assume that the "hidden" cone inside
the rotor is identical with the other "visible" cone, so in case off
pitted cones, just order to two "visible" cones.

Be prepared that it may take longer than you thought it would, so
don't do it if you need the wheel later in the day, or early next
morning.

AFAIK, the rotor doesn't loose its magnetic power when out of the hub
shell like some old SA generator hubs did.

[Andrew]

The document is now available from here for those interested.

[vorsprung]

I managed to take my shimano dh-3n71 apart once, bit of grease on the easier to get at bearings.  I could see the other bearings but getting at them was more involved.  I had another go, got a bit further but after this the generator hub was broke, the wire attaching to the coils inside snapped.  It couldn't be reattached with my level of electrical repair so I had to buy another hub and rebuild the wheel

So can I just emphasise- it is very easy to break the wires in the hub, be very careful

[andrew_s]

I've found a copy of the original Trinity Bicycles web pages that have clearer photos than Andrew's pdf.
If anyone wants a copy, PM me and I'll email them (806kb zip). Be warned that I'm often a bit slow noticing that I've been PM'd.

[geoff]

Me? I hamfistedly broke the wire in mine when it was almost new, in one of those "I wonder what this does?" moments.

But having built the wheel it was in, I wasn't about to abandon the hub. So I soldered another wire back on it (and I am the world's worst solderer). Somehow it's still working 2 years later - a testament perhaps to the amount of over-engineering in even the cheapest of generator hubs.

[mmmmartin]

Thread resurrection warning. (And what a remarkably useful forum this is, BTW.)
My wheel with the Shimano hub dynamo is noticeably rocking, about 3mm side-to-side at the top. I fear new bearings are needed. Having checked on the other wheel with the Shimano hub dynamo, this one does not rock at all. On the "good" one I've done about 8,000k, almost all with front panniers and often on terrible road surfaces. The "worn" one has done at least twice that but usually on decent tarmac and hardly any loads.
I'm going to ignore this problem until it goes away.

[andrew_s]

Have you tried adjusting the bearings?
Shimano hub dynamos are normal cup & cone. The awkwardness is the fragile wires threaded through the connector side bearings.
If you don't want to risk it, you can regrease and adjust the bearings at the non-connector (left) side as normal, and whilst you have the left side cone out, you can try pushing the whole axle across and see if that exposes enough of a gap behind the dust shields at the right side to inject extra grease in though with a grease gun.

[Brucey]

I agree some bearing adjustment seems in order as a first step.  With no little care, and a very thin nozzle extension, it is often possible to add grease to the RH bearing in a shimano generator hub. The LH bearing can be serviced just like any other cup and cone hub.

In most shimano models the LH cone is available as a spare part and it will fit in the RH side if you are brave enough to risk breaking/damaging the output wire.

FWIW DH-3N71 has (had) an inherent weakness; the cones have an insufficient wall thickness and tend to break up. I'm not sure you can get spares any more, and even if you can find them, they may not last forever.

IME shimano hub generators benefit (moreso than other hubs with similar bearings) from having the bearings regreased on a regular basis in all-weather use; this is because  there is a large airspace in the hub that 'breathes' with temperature changes. This can lead to condensation inside the hub, as well as the hub actually drawing water inside when it rains, eg when a warm bike is taken out into cold rain.

cheers

[Dave_C]

Great that this thread has been resurrected as I gave my summer audax bike a service last night. One pedal was seized and I notice the DH 3D80 dynamo hub was VERY still top turn. I have another with many more miles on and its has never given any problem, same hub. So I'll have a shufty this evening and hopefully be able to dismantle the hub to re/grease/place the bearings.

Darn, I sent an order to CRC this morning, I should have waited, I would have been able to add a 15mm spanner also...
Cheers. Dave C

[Dave_C]

Additional Question:

Where from (UK) and what cone bearings would I order please?

I understand cone bearings and the adjustability of then (I use to do the bearings on the back of my mini myself).

Cheers, Dave C

[Palinurus]

Glad this appeared in my unread threads today. May well need it soon.

[Dave_C]

Glad this appeared in my unread threads today. May well need it soon.

I found this, it is in German, but gives a good close up in focus (most of the time) video of the assembly. It looks like the maker of the video may have changed the single copper wire for an insulated and multi thread wire, making if easier to handle.

https://www.youtube.com/watch?v=CZVWNUYbgDc

I'll be going to that 'What grease' thread to ask, can I use my 'usual' grease to lubricate the bearings..... ;o)

Dave C

[Brucey]

use the best grease you can, ideally waterproof with corrosion inhibitors.

When adjusting the bearings, do bear in mind that the QR will compress a hollow axle somewhat when it is tightened, and this affects the bearing clearances.

 The correct adjustment is (with locknuts tight) a little free play that just disappears as the QR is tightened.

For cones etc you ought to be able to order them from

- any shimano stockist
- several of the large german retailers
- SJS have stocks of many of the more common parts

You can find the correct part numbers by finding the 'EV techdoc' for your model shimano hub.  Once you have the full part number, try googling it in order to identify suppliers.

However because of the way that these part numbers work/are listed, it is worth trying

a) without the first and last digits to the part number and/or
b) with different punctuation in the middle, i.e. with space, or with hyphen, or without either.

cheers
 

[Dave_C]

use the best grease you can, ideally waterproof with corrosion inhibitors.

When adjusting the bearings, do bear in mind that the QR will compress a hollow axle somewhat when it is tightened, and this affects the bearing clearances.

 The correct adjustment is (with locknuts tight) a little free play that just disappears as the QR is tightened.

For cones etc you ought to be able to order them from

- any shimano stockist
- several of the large german retailers
- SJS have stocks of many of the more common parts

You can find the correct part numbers by finding the 'EV techdoc' for your model shimano hub.  Once you have the full part number, try googling it in order to identify suppliers.

However because of the way that these part numbers work/are listed, it is worth trying

a) without the first and last digits to the part number and/or
b) with different punctuation in the middle, i.e. with space, or with hyphen, or without either.

cheers

Hi Brucey,

This is great, many thanks for taking the time to give us all this useful information.

Dave C

[BrianI]

Glad this appeared in my unread threads today. May well need it soon.

I found this, it is in German, but gives a good close up in focus (most of the time) video of the assembly. It looks like the maker of the video may have changed the single copper wire for an insulated and multi thread wire, making if easier to handle.

https://www.youtube.com/watch?v=CZVWNUYbgDc

I'll be going to that 'What grease' thread to ask, can I use my 'usual' grease to lubricate the bearings..... ;o)

Dave C

Great video, it does indeed look like he has soldered on an insulated multi cored wire.  Amazing what you can find on youtube.  Both my dyno hubs are working well, but at least I know they are serviceable with care. 

[mmmmartin]

Thread resurrection warning. (And what a remarkably useful forum this is, BTW.)
My wheel with the Shimano hub dynamo is noticeably rocking, about 3mm side-to-side at the top. I fear new bearings are needed. Having checked on the other wheel with the Shimano hub dynamo, this one does not rock at all. On the "good" one I've done about 8,000k, almost all with front panniers and often on terrible road surfaces. The "worn" one has done at least twice that but usually on decent tarmac and hardly any loads.
I'm going to ignore this problem until it goes away.

Am embarrassed to say nothing has been done about this, so I did a search and found my post saying a year ago there was a problem and I was going to ignore it until it went away. It hasn't gone away.