Just over a year ago, I acquired a bicycle – a Surly Karate Monkey (http://www.14degrees.org/en/?p=1547). Stock standard, the bike is a single-speed. In other words, it has only one gear. This is not conducive to the most efficient cycle touring in the world, so I splashed out and changed to a Shimano Alfine 8-speed internal gear hub (IGH).
As you can see, there one cog on the outside, and all the gears, in the form of, literally, gears, are on the inside of the hub shell. The beauty of this setup is that a bicycle with an IGH essentially becomes maintenance free (when one compares with a typical derailleur setup, where you have to clean multiple oily cogs quite often).
IGH’s do need maintenance every now and then, though. I’ve heard of some going for three years before being opened up, and the insides looking like new, but after one year, mine was starting to act up a little; a little more friction than usual, and it was sometimes taking a full half-rotation of the pedals in order for the drive to engage after free-wheeling. I live in Sapporo, Japan, and even though this is the land of Shimano, IGH-equipped bikes are extremely rare here, so there was little to no chance of having the hub serviced locally. Therefore, I decided it was time to pull the thing to bits and have a gander.
The most useful resource for learning about how to pull a Shimano Alfine 8-speed hub to bits was this video below.
Other resources included Nick Foster’s very recent post, of course Muddymole’s post, Ian’s page about the Nexus hub and adding an oil port (similar to the Alfine, but with less sealing), Lachlan Hurst’s post, wisdomfrom Ecovelo, bike mechanic Sam Larson, Thad at the Golden Wrench and his experiences, Aaron’s Bicycle Repair’s great resource, Sheldon Brown’s advice on lubrication for IGH’s, and last but not least, Hubstripping.com’s page on the Alfine 8-speed hub.
How to Do an Oil Bath on a Shimano Alfine 8-Speed Hub
Some people have reported being able to screw open the dustcap by hand (it screws open clockwise, which is opposite to normal), but I had to take to it with a screwdriver to loosen it a little. Once the dustcap comes free, the whole hub shell will fall away from the insides.
On my hub, I noticed right away that water had entered the hub at some stage. I do vaguely remember the non-drive side cone being loose at one stage, and suspect that this was the culprit. If the cone is on properly, then the rubber seal should prevent any water from getting in. The rusty residue was not too bad though, and wiped off easily. After cleaning the hub shell, however, there were some visible blemishes on the bearing race, but no noticeable pitting.
To remove the drive-side bearing cage, the hub needs to be split into two pieces. This is achieved by removing the snap-ring at the non-drive side of the unit.
The whole axle unit slides out of the main ring gear unit in two bits (explosion drawing here). There was no visible rust residue inside, so that was reassuring. I cleaned up the drive-side bearing cage, re-greased it, and put the two pieces back together. This is done by lining up the tab on the ring gear unit, and the groove in the axle unit. Even when the tab and groove are lined up, however, the gears need to be rotated around a little to get the ring gear unit to mate to the axle unit (this can take a while to get right).
Everything back together, with snap-ring re-installed, the whole lot gets dunked in auto transmission fluid. Mine was just normal, service station (gas station) ATF, using a 2 litre PET bottle as a dunking container.
I left it in for about 5 minutes, and then let it drain for about 10 minutes while I was re-greasing the insides of the hub casing.
It is really important at this point to allow the hub to drain well. If too much ATF is left on the hub, it will leak out of the disk-brake (non-drive) side of the hub. If you have a disk brake installed, this will cause ATF to leak onto the disk, ruining your day.
The innards then went back into the hub shell, the various dust covers put back on, the cog and snap-ring (which can be infuriating to get on) and the gear-shifting accessories. And then I took it all to bits again. No joke. I had put the drive-side bearing cage on the wrong way around. The picture above shows it in the correct orientation. That was not a happy moment when I had realised I had put it on wrong…
In all, it took me about 45 minutes plus another 20 minutes to rectify the bearing cage issue. Next time it will take around 30 minutes, I would say. That’ll probably be in another 12-18 months time.
Without the oil bath, the hub just has grease inside it. This means there is quite a lot of friction. For example, when back-pedaling the bike on a workstand, the back wheel will start to rotate backwards. With the oil bath, however, backpedaling does not affect the back wheel. I didn’t notice any difference in gear changing; that is as smooth as ever.