Stiff Dyno hub

[quixoticgeek]

My DH-T8000 Dyno hub arrived in the post this week, I took it out the box thinking to spin it between my fingers to check it works. And I couldn't get it to move. I was expecting it to be knotchy, nearly every article about dyno hubs mentions this, but to not spin at all? That surprised me. I'm guessing this is Yet Another Case of Shimano QC™ being poor.

Does anyone have any suggestions on how best to adjust the bearings on this hub? One side seems pretty obvious (based on the exploded diagram). But the other side, I'm guessing they are embedded in the "internal assembly", and aren't easy to adjust?

Any ideas?

J

[Hot Flatus]

Send it back

[quixoticgeek]

Send it back

Not exactly trivial, It came from Germany. If it's just a case of bearings adjustment, I'd rather hang on to it.

J

[Hot Flatus]

It is of course up to you, but it is a £100 hub with some fragile wiring inside.

I wouldn't want to risk invalidating the guarantee.

[LittleWheelsandBig]

Clamp the hub in a fork and then spin it. You should feel it 'cogging' as the magnets line up.

If you do want to adjust the bearings, only move the cone and locknut on the opposite side to the cable connector. You won't need to loosen them off very much.

[grams]

Do you mean it literally won't move at all, or that it jumps to the next notch rather than spinning?

(The latter is normal)

[Polar Bear]

I recall the first time that I bought a dynamo hub: a lovely SON.  I too wanted to irrationally spin it but it was a stubborn beast.  However, it's been providing faultless service since 2004.

I would recommend securing it in the fork dropouts, then turn the dynamo body by hand.  It should feel alternately very resistant, then almost spring forward to the next notch.  It's a very non-intuitive experience as you expect a hub to spin quite freely.

Alternatively, take it to your local lbs and ask their opinion.   

[Polar Bear]

Schezbzflat! My hub feels notchy!

When you hold the wheel or hub in your hand and turn the axle, you'll feel a lot of resistance. There are 26 poles and 26 magnets in the SON28 hub (fewer in the SONdelux). That creates 26 points around the hub shell that the axle wants to settle in, and a corresponding 26 points where the axle doesn't want to be. In the transitions between those points, the axle wants to turn in one direction or the other, to find the point where it wants to settle. As you ride, the hub turns relative to the axle, and 26 times in each rotation of the wheel, the hub wants to turn one way, and then the other, theoretically speeding you up and slowing you down, 26 times per rotation. At speed, the effects of these two forces almost completely cancel each other out, leaving you with extremely low drag overall. It's only when you don't have a lot of mass (your weight) and inertia (your speed) that the effect is to actually retard the rotation of the hub axle. So there's no reason to be concerned about the way the axle feels when turned by hand.

Scroll down a fair bit to find the section on notchiness.  Though your hub is a Shimano the principle is just the same.

[Brucey]

the Peter White advice is spot on for hub generators that have cartridge bearings inside. I would advise that you don't bother to do anything to the hub until the wheel is built.

However.... IME all models of shimano hub generators are invariably shipped with the bearing adjusted way too tight.  If you do not correct this situation the hub will stand a pretty good chance of knackering itself prematurely.

 My record is a DH-3N72 which had the NDS cone backed out 1/4 turn before the bearings were correctly adjusted.  Between that and dry lip seals which needed more, better lubricant, the hub suffered an additional parasitic loss that I estimated (using run-down tests) of over 1W. [BTW I wonder if reported test data   of hub generators allows for this kind of thing; I suspect not...]

However the actual preload on badly adjusted bearings isn't quite as high as with other types of hub, because the shell stiffness is less on a hub generator. Even so I would be very surprised if the bearings in you hub generator don't benefit from more, better grease, and a better adjustment.

If you are running disc brakes then there is an argument (for hub generators only) that the usual adjustment (a little free play that just disappears as the QR is tightened) results in a bearing that moves around a bit when the brakes are on.  I'd still adjust so that there is a tiny bit of free play when the QR pressure is off though.

cheers

[Samuel D]

After ascertaining that the hub works (which might require surprising force to turn the axle for the first time – your fingers may not be strong enough to do this on a loose hub, so clamp it in a fork and turn the hub instead), you should build the wheel. Only then is it possible to set the bearing preload correctly. Spoke tension in the built wheel can change the preload slightly but noticeably, and checking for free motion at the rim is the easiest way to observe play in the bearing.

[Brucey]

shimano don't use white grease in hub generators (not that I have seen, maybe someone knows different?) and the grease they do use is applied in parsimonious quantity, so that probably means that someone did you a favour and added some more/better grease to the hub. 

It is quite normal for excess grease to work its way out of bearings as you describe. 

BTW the thing that stops the seals from working (and also increases the seal wear rate) is if the seal lips run dry. It isn't a bad idea to apply a squirt of spray lube externally, eg aerosol semi-fluid grease (NB not  other forms of spray grease) to ensure that the seals are kept happy. Do this once every few months, and simply wipe off the excess.

cheers

[quixoticgeek]

Thanks Brucey. The wheel was built by Spa Cycles, so maybe they did something.  I've emailed them to check.  It reminded me of the time my headset bearings expelled a load of brightly coloured snot.

In the process of building this bike I've been quite generous with the grease, I'm fully expecting to find all sorts of blue snot oozing out of various parts as I ride the first few hundred k. Made me wonder if it's possible to use too much grease...

J