Inside the Sunrace-Sturmey 8-speed
The new one is fab, but the old one broke. We take it apart, find the fault and reassemble. Warning for dial-up readers: report contains 46 images...
As some of you may already have read over in the VV Forum and as hinted at in VV18, the third of the Sturmey-Archer 8-speed hubs I've tried broke recently.
I know a number of readers have been following the ongoing reports in the magazine about my experiences with the Sturmey-Archer 8-speed hub with interest. It seems I was sent a number of hubs which weren't really fully-developed - and I've broken three so far. But fingers crossed, it looks like they might have cracked it now...
The good news is that the new one they sent, which I built into a wheel for my town bike and have been using for a few weeks now, is MUCH better. Shifting is far more precise than ever before, it's still lovely and silent, and feels pretty efficient too. I've also heard similar very positive reports from Tony Hadland who also has a latest-generation Sturmey 8-speed. Apparently someone who tried his, a Rohloff user usually, compared the Sturmey's shifting favourably...
If the hub is now mature, many people are holding out hope that it'll be squeezed into a Brompton rear triangle before long... finally giving that bike a decent range of gears at a feasible price.
Anyway, in the meantime I thought I'd have a go at taking one of the old ones apart - Sturmey didn't want it back, as it failed from a cause already known by then. I don't think they should mind me showing detailed pics of the innards - any competitor wanting to copy the hub will simply have bought one. But realistically, there's such a tooling cost involved anyway that this is pretty unlikely.
Please note this is not an 'official' guide about how to do it. No doubt, expecially when reassembling, there are alignments to be observed and torque settings to be adhered to. It's for interest only.
We'll start with the hub, with sprocket and axle nuts removed:
First stage is to remove the circlip:
This releases the shifter cable support plate and a washer:
This exposes the drum which the gearchange cable wraps around and rotates to change gear. Remove the nut, and this and a few spacers are released:
Another plate is exposed:
This just pulls off, revealing the first set of bearings.
The hub had been used hard for six months or more, but the bearing races look like new:
Pull off another plate and you can see the spring which tensions the gear change cable. Note also the still-clean grease on the ball race.
These parts also just pull off now. The ballrace is secured behind a press-fitted sealing ring, so I couldn't remove it. There was also a thin cylinder-ring type seal in a groove around the outside, seen below the part.
Inboard of this ring is another bearing surface, again gleaming as new.