Background

My first Shimano hub gear only lasted two years before failing catastrophically. Dismantling it after failure it was evident that it had let water inside and there was lots of corrosion. It's not a pretty sight, but the full detail (and nasty pictures) is listed on another page.

Modifications

Recalling that good old Sturmey-Archer hub gears work forever, withstanding any abuse as long as they get an occasional dose of oil through the hole in the shell, I decided to see if I could put an oil port in the new hub.

Trial on the Old Hub

As a first step, I put an oil port in the old hub.

This is not terribly useful, to be honest, because the hub doesn't work without the large ball race working, and I can't fit the balls in that without a new ball carrier. By the time I tracked down a new ball carrier, I'd bought a completely new hub. However, I didn't want to start being too destructive to a brand new hub without a trial run.

The first step was to open up the hub, measure it, and draw it out to a reasonable accuracy. This is what that process gave.

It suggested that there was a reasonable thickness to the shell, and a location which gave some space on the inside. As a bonus, it was right alongside the carrier, meaning that if you poked anything through a hole at this location, it would rub on the carrier, but not snag in any mechanism. A good place to put a hole.

My plan was:

  1. Glue (araldite) a washer on the outside of the shell to provide a flat seat to seal against.
  2. Drill and tap an M4 hole through the shell.
  3. Use a nylon screw and o-ring (or rings) to plug the hole.

The reason for a nylon screw was that I wanted to avoid galvanic (bimetallic) action between screw and hub, especially as if I put in an iron-based screw, the aluminium would tend to act sacrificially, and I don't want the thread to erode. I also wanted a soft screw, so that in the event of abuse, the screw is wrecked, not the hub.

Basically, the trial went to plan. The shell is a little thinner than my measuring suggested, but the hole comes out in the right place and seemed like it would work (if the hub still worked).

Washer on the outside. Shell surface treatment rubbed off with sandpaper.

Comes out in the right place inside.

Nice nylon M4x10 screws with knurling for doing up by fingers from ebay (wildangel tattoo - I have no idea what tattooists do with M4 nylon screws). M4x8 would be better, but that's easily achieved with a stanley knife.

Installation into New Hub

So there seems to be no reason not to install it in the new hub.

It did take me more than a year to get round to actually doing it, however. The only thing I've done differently is use a metal-specific epoxy glue to bond the washer. I don't actually believe the epoxy is anything other than coloured silver - the packet makes a big thing about it being for metal ("ideal for all metals including steel copper aluminium & cast iron") but any old epoxy will do that.

The added complexity of this process is that I've done it with the wheel built up (as you can see), though I did slacken the spokes to displace the rim a bit.

Unfortunately, Shimano has changed the outside profile of the hub (apparently only for aesthetic reasons), which makes it a bit more difficult to locate the hole. It's not completely obvious, but the red stripe has moved about 5mm across the hub (towards the middle). The problem with this is that the stripe lies in a groove, with a distinct edge (see the cross-section drawing above). I had to put the washer overlapping the edge (as shown here), ...

... and it still barely cleared the internal race.

Actually, I must confess to a bit more luck than judgement here - this is even tighter than I expected when I set it out. If I were doing it again, I would probably move the washer back to the same position as in the trial, and live with the fact that it's across the shoulder. That may make the drilling more difficult, but if (as I have) you fill up the washer with epoxy first it might not be so bad.

Again, the contrast between a properly sealed hub (here) and the same races in the inadequately sealed first one (up four pictures) is marked.

Done (I've trimmed the screw so the internal projection is OK with just one external o-ring).

I put some grease in the mechanism, and re-greased the internal races with Shimano's dedicated grease. The service instructions say you must use their special grease, but it looks like a fairly standard white bicycle waterproof grease to me. However, since I have a tube, I used it.

When I re-assembled the mechanism, I added a band of (green) adhesive tape over the push-fit plastic cap. I don't know whether it is necessary, whether it will actually improve the seal, or how long it will last, but it will be easy to remove so won't do any harm.

I also add a generous dose of grease behind the metal plate (ie, between the metal plate and the plastic cap). This is to discourage any water making its way through there, and having used a fairly thin grease, I think the added drag is negligible.

Testing

First step was simply to reassemble the hub and ride it without doing anything more. I rode it for two weeks without further work, so as to establish that it was back together properly.

Once I was satisfied that I hadn't broken anything, I added 10ml of Shimano's blue dipping oil and waited to see what happens. Nothing happened, basically - the hub continued running fine, with no detectable difference. Since I wasn't trying to improve performance, no change is probably good. The other good news was that no oil-spots appeared on the floor beneath the bike, either where it lives at home, or where it lives at work.

Four weeks later, having done nothing further in the meantime, I took the screw out and set the hub with the hole at the bottom to see what would drain out.

It took about ten minutes before the first drip appeared, but then over the course of half an hour or so I got about 3ml of oil out. It's dark grey coloured (the clean oil is blue), but the feel and viscosity is about the same as new oil, at least qualitatively. The old oil is a bit less mobile (I dropped some onto printer paper - new soaks in and spreads out quicker, and gets through to wet the second piece).

I'm encouraged by this - a delay until the oil comes out suggests that it distributes around the innards, it's not all just pooling at the bottom of the shell (that would be unlikely - it's a reasonably viscous oil). The fact that I got some oil out means that it hasn't all escaped or evaporated - there's still 'spare' oil after a month of use. I'd hope quite a bit remains coating the innards, so getting out about a third of what I put in seems a good result. It's a bit contaminated, but actually it's hard to expect otherwise after a month in a gearbox that wasn't cleaned out to start with.

Also, 10ml is actually a puddle less than one millimetre deep if it extends the whole of the hub shell, so it could have distributed round the inside of the shell without getting to the bits that matter. Since it came out grey, I'm assuming it has at least got to some moving / sliding parts to do some good. If it got to some, I'm assuming it distributed around all of it. That's possibly a big assumption, and some time I'll open the hub again to see if it looks oily throughout.

I've put another 10ml (all clean) back in.

Longer Term

There's a one-year-later page about what I found nearly a year after putting in the oil port, and one after eight years use too.



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