Shimano DH-3N71 (and 3N70 etc...) cone cure?

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Brucey
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Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby Brucey » 8 Jul 2013, 5:58pm

various folk greeted shimano's 'ultegra level' hub dynamos with some enthusiasm when they first came out, but then the plaudits turned sour as the hubs failed, often at low mileage.

Previous shimano hub generators typically made a decent 3W output, but were rather draggy doing it. Some even dragged worse with the lights off than with the lights on! The improved generators like the 3N71 were lighter, more efficient, and had smoother bearings. What could possibly go wrong?

Well, all shimano hub generators (and many others) have a fundamental flaw in that they have an appreciable airspace inside them. The airspace 'breathes' via the bearing seals anytime the temperature changes. If it is raining when the hub cools down, it simply sucks water inside. This seems to happen on the right side more than the left, possibly because there is a crevice which can hold water, just next to the seal and the connector housing. The water goes straight into the bearings.

The left side bearing is easily accessed, cleaned, regreased and adjusted in the normal way. However (although it is possible to do so, with care) the right side bearing is not meant to be serviced according to shimano; the spare part they sell is the whole generator winding, axle and RHS bearing/bearing housing. This part costs as much as new hub IIRC. To cap it all, the RHS bearing sees more load than the left, because the bearings are not symmetrically positioned in the hub. The RHS bearing might see about double the load of the LHS bearing because of this.

So all shimano hub generators tend to eat their RHS (and/or LHS) bearings, in a perfect storm of poor maintenance, extra load, and water-contaminated lubricant. These failures tend to be progressive, with hubs needing more and more frequent adjustments, and even 'bleeding' horrible rust-stained stuff from out of the bearings.... I have pulled ball bearings out of such a hub that were genuinely 0.5mm undersize through wear and corrosion... But.... 3N70 and 3N71 hubs have an extra problem, over and above those of other shimano generator hubs.

The extra problem with the -70 and -71 hubs appears to be that the cone can break up into tiny pieces, rendering the hub scrap in a short period of time. The failure is accompanied by lots of clunking and grinding noises. When the wheel is removed, often the hub won't turn at all.

Peter (aka 'Interested CP') sent me some pictures of failed cones from these hubs.

The design is poor; the cone is only 0.5mm wall thickness from the thread root to where the balls might run. This isn't enough, really. Throw in hard, brittle steel and maybe some slightly excessive bearing preload (no play with the QR loose means the bearing is too tight BTW) and the cones will fail anyway. Add salty water in the usual way and the hub won't last a single winter.

I recently obtained a worn hub and sure enough both bearings were rusty and although the cups were not that bad, the RHS cone was all broken up to the point that it couldn't be safely run any more.

Even though the DH-3N80 model has only quite recently supplanted the 3N71 etc, I was surprised to find that the correct replacment cone ( which is the same as the LHS one) for the 3N71 is not available in the UK, perhaps anywhere. This made me sulk somewhat; not that I needed to use the hub, but I had hoped to be able to run it to carry out some electrical measurements, at least.

After a little cogitation I decided to see if I couldn't make my own cone for the RHS bearing at least. Scouring the shmano parts database soon revealed that there were other M11 cones that I might be able to regrind to suit. If I also fitted more, smaller balls to the hub, maybe I could make it work again, this time with a cone that has a sensible wall thickness.

The photo shows what I did; on the left you can see a reground cone, which instead of running on 10 or 11off 3/16" balls now runs on 14off 5/32" balls.

DH3N71 v3.jpg
almost looks like the real thing...?


You can just see a brown line on the new cone where I checked the contact angle of the assembled bearing on the left side of the hub. The cone surface (which I had removed ~0.75mm from) seemed still to be quite hard (to my surprise). In case you are thinking I must have used some fancy gear to reprofile the cone, I didn't; I did it ghetto style.... I mounted it in on arbor in a clamped electric drill, then set it going at 2000rpm whilst I attacked it with an angle grinder. Once I had the shape and size I was aiming for, I polished it (a little...).

I was sufficently encouraged to build the hub into a wheel and run it for a while, with a revised RHS bearing and an original style LHS bearing. I've done about 60 miles so far and the bearings have not needed adjusting yet. To me, this means that if the new cone is softer, it isn't very much softer, and maybe I've worked up a scheme for rescuing these hubs.

If the hub falls apart or continues to work OK I shall post here and let you know, either way.

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

rjb
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Re: Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby rjb » 8 Jul 2013, 8:54pm

Angle grinder :) beats trying to do it with emery paper while spinning it in an electric drill :wink: . Will file this one for future use. You need to publish all these hint's and tricks in a database Brucey
At the last count:- Focus Variado, Peugeot 531 pro, Dawes Discovery Tandem, Dawes Kingpin, Raleigh 20, Falcon K2 MTB dropped bar tourer, Longstaff trike conversion on a Falcon corsa. :D

Brucey
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Re: Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby Brucey » 16 Jul 2013, 10:49am

rjb wrote: .... Will file this one for future use. You need to publish all these hint's and tricks in a database Brucey


-probably, yes... I'm thinking of this....

BTW an update on the DH-3N71; ~150 miles so far, and nothing alarming has happened.... yet..... :shock:

cheers
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interestedcp
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Re: Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby interestedcp » 17 Jul 2013, 6:34pm

Nice job with the spare cone. It is probably much better than the original.

In principle, any Shimano (or Campagnolo) certified dealer should be able to get any spare part. They again get them from their country's Shimano importer/distributor. However, the local distributor may only carry a subset of Shimano's entire catalogue of parts and spare parts. So it is sometimes worth it to use a shop in another country with a different distributor. When it comes to dynamo parts, the German Shimano distributor "Paul Lange" probably has the largest selection in the world. Here is a blurp on how they carry 7600 different Shimano spare part numbers (total stock of 300.000 units).
http://www.bike-eu.com/Sales-Trends/Ret ... -1094759W/

Some years ago when I ordered spare cones for my Shimano 2N70, at Rosebikes, they said that they could get any Shimano or Campagnolo part by mailing their sales department with the correct spare part number from the technical pdf's. (Like; Cone for Shimano 3N71, Shimano spare part # "Y-20D 98020").

I can't find my old email exchange, but I remember the "Y-20D 98020" cone being quite expensive, much more expensive than eg. the Shimano Ultegra cones they normally carry. But at least Rosebike could get it (and fast too). I appended the order to another order from Rosebikes I had to do anyway to avoid extra postage. It is possible that Rosebike still can get cones for 3N71 hub dynamos.

Personally I have decided not to buy a new cone for my 3N71, since I fear spending good money on it, just for it to break after a few years. I dislike not repairing things, but for my use, the 3N71 simply isn't durable enough. I have several other Shimano hub dynamos, and have been using a 3N80 year round since January 2008 without any problems.
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Regards

Brucey
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Re: Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby Brucey » 17 Jul 2013, 7:43pm

I did wonder if it was just Madison )shimano UK agents) being useless or if Shimano was at fault. They do stop spare parts for old models after a few years, but it seems a bit early to stop the DH-3N71 spares. I sent an e-mail to madison enquiring 'why no spares?' and received no response whatsoever. Typical.

BTW I was wondering whether it was worth the effort, but one thing that swung it was that the cone I used for my experiments was dead cheap; about £2 I think.

cheers
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Jay Gee
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Re: Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby Jay Gee » 17 Jul 2013, 8:11pm

The pleasure from my first wheellbuild already spoiled after hassles with the Chrina rims; now I find the hub was a bad choice too!

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7_lives_left
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Re: Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby 7_lives_left » 18 Jul 2013, 12:14am

That's a smashing idea Brucey.

I was wondering if it might be an idea to change both the left and right cones at the same time. Do you want the contact angles to be the same on the L and R sides?

Also your inability to get the cones out of Madison might be down to me. Several years ago I put an order in to my LBS for some cones for an Alfine dynamo hub that look remarkably similar to the ones in you picture. I asked for 3 off. I kept pestering the LSB for about 4 months. Eventually they got some out of Madison. But I could only have two pieces and I was told "You can't have any more, there are no more in the country". I was changed about £15 each, with a "CTC discount".

I also have an Alfine SG-500 model A hub that has a dodgey L hand cone. I have been told I can't have a replacement for that. Maybe I could try your trick to get that hub back into service.

PS it was riding through a flooded River Ouse around York and then neglecting to regrease the hubs for several months that did the damage in my case. Lesson learned the hard way. I had problems with the bottom bracket too.

Brucey
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Re: Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby Brucey » 18 Jul 2013, 5:16am

7_lives_left wrote: ...I was wondering if it might be an idea to change both the left and right cones at the same time. Do you want the contact angles to be the same on the L and R sides? ...


most hub bearings are set up with identical contact angles each side. However, if the bearing has any slack in it, or the parts flex at all under load ( most do) and the radial loads are not equal, then there is an argument for having contact angles that more closely match the radial loads on each bearing. If they do match the load properly, then the side thrust generated at each bearing will be equal, and the balls won't scuff so much in normal use. In extremis, such matching cannot be carried out (and I'm thinking of quite a lot of Campagnolo rear cassette hubs here) and a pair of such unevenly loaded angular contact bearings may need slightly greater preload than normal in order not to wear prematurely through such scuffing.

Of course I should point out that Shimano rear hubs are not immune either, since they (unlike Campag ones) see the chain loads too, and these load the bearings unevenly also.

So I chose a slightly steeper contact angle for the RH bearing, because it is more highly loaded in this hub. This also has the slightly devious advantages of lowering the contact load slightly, and putting the new, smaller, balls in contact with a less worn part of the cup in the hub, too.


I also have an Alfine SG-500 model A hub that has a dodgey L hand cone. I have been told I can't have a replacement for that. Maybe I could try your trick to get that hub back into service.

PS it was riding through a flooded River Ouse around York and then neglecting to regrease the hubs for several months that did the damage in my case. Lesson learned the hard way. I had problems with the bottom bracket too.


Unless the Alfine hub also has a defective design, I'd suggest (as Peter says) trying for the correct part elsewhere e.g. in Europe before making one like I did. I don't think Madison stock everything they should do. Obviously if the LH bearing is bad, the RH one will likely be too, and if it follows suit with other shimano generator hubs then the cone will be the same part, just difficult to access. If the cone and balls are not too bad, it is (with the LH bearing slackened off) usually possible to open the RH seal far enough to clean and add fresh grease to the RH bearing without dismantling the hub fully.

Floods may have given your hub and BB the kiss of death, but they are designed and manufactured in such a way that

a) the water can get in past the seals, and

b) the expansion and contraction of the airspace within each will positively encourage this to happen.

cheers
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interestedcp
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Re: Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby interestedcp » 19 Jul 2013, 12:13am

Jay Gee wrote:The pleasure from my first wheellbuild already spoiled after hassles with the Chrina rims; now I find the hub was a bad choice too!


Well, I did get several years of daily use out of my 3N71 before the cones were knackered. There wasn't any play in it before QR tightening (I was too scared to touch it then), and those riding it ,including me, wasn't exactly featherweights. It was on loan the last year I had it, and come to think of it, it was probably stored in a somewhat humid cellar. I think Brucey is spot on when it comes to describe the several factors that can conspire to make it fail too soon. The correct amount of bearing play before QR tightening, and a yearly inspection of the "easy" cone, would probably prolong its life expectancy quite a bit.
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Brucey
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Re: Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby Brucey » 5 Aug 2013, 10:23am

update; about 300 miles in, DIY cone still working just fine, no slack in the bearings yet (which given how I have adjusted them, would happen very quickly if there were any wear whatsoever)

cheers
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fatboy
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Re: Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby fatboy » 9 Aug 2013, 12:10pm

interestedcp wrote: The correct amount of bearing play before QR tightening, and a yearly inspection of the "easy" cone, would probably prolong its life expectancy quite a bit.


I went to do this on my 3n80 but found that I need a bigger cone spanner than I own. Does this mean that the 3n80 has a better cone? Does anyone happen to know what size the cone spanner needs to be?
"Marriage is a wonderful invention; but then again so is the bicycle puncture repair kit." - Billy Connolly

Brucey
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Re: Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby Brucey » 9 Aug 2013, 12:18pm

the 3N80 has a fatter 14mm axle and different cones from the 70/71/72 series. AFAIK they don't break up but they can still let the weather in eventually.

I'm not sure what the cone spanner size is, but it might be 19mm. You will have to measure it to be certain I think.

cheers
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fatboy
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Re: Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby fatboy » 9 Aug 2013, 2:21pm

Brucey wrote:the 3N80 has a fatter 14mm axle and different cones from the 70/71/72 series. AFAIK they don't break up but they can still let the weather in eventually.

I'm not sure what the cone spanner size is, but it might be 19mm. You will have to measure it to be certain I think.

cheers


Hopefully good news. I will measure the nuts (they're nutted rather than the normal cone flats). I will measure, just wondered if anyone could save me the bother! I was feeling brave last night but fell at the first.....may be a while before I feel brave again!
"Marriage is a wonderful invention; but then again so is the bicycle puncture repair kit." - Billy Connolly

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CREPELLO
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Re: Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby CREPELLO » 9 Aug 2013, 3:10pm

I've got a couple of T660 LX dyno-hubs. Would these be based on the 3N80 design, or the older 3N70?

Brucey
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Re: Shimano DH-3N71 (and 3N70 etc...) cone cure?

Postby Brucey » 9 Aug 2013, 3:49pm

there are some techdocs here;

http://www.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/DH/EV-DH-T660-2846_v1_m56577569830648091.pdf

and here;

http://techdocs.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/DH/EV-DH-3D72-2858A_v1_m56577569830728402.pdf

Although the cone part numbers are not identical, and the integral dust shields look a different shape, somewhat ominously the axle threading and the number of ball bearings is the same, hinting that the bearing cones may have a similar profile.

cheers
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