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...

Posted by Peter Eland on Wednesday 22 Jun 2005

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:

Sturmey pic

First stage is to remove the circlip:

Sturmey pic

This releases the shifter cable support plate and a washer:

Sturmey pic

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:

Sturmey pic

Another plate is exposed:

Sturmey pic

This just pulls off, revealing the first set of bearings.

Sturmey pic

The hub had been used hard for six months or more, but the bearing races look like new:

Sturmey pic

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.

Sturmey pic

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.

Sturmey pic

Inboard of this ring is another bearing surface, again gleaming as new.

Sturmey pic

Next pop off a plastic shield and you can unscrew (left-hand thread) the large-diameter outer race. This screws into the hub with a fine thread. You really need a large pin spanner to remove this, or a special tool. Again, bearing surfaces pristine:

Sturmey pic

At this point the hub innards are ready to come out:

Sturmey pic

But first you need to flip the hub round and release the hub brake parts:

Sturmey pic

Just undo a few nuts and it all pulls off:

Sturmey pic

Just the cone left:

Sturmey pic

and you can pull the innards out leaving the hub shell:

Sturmey pic

Inside there's a freewheel ratchet ring and axle bearings, again with clean grease:

Sturmey pic

The innards are one solid lump:

Sturmey pic

And a reverse view:

Sturmey pic

The reason for the hub's failure is now revealed, too:

Sturmey pic

The ring gear has burst in two places:

Sturmey pic

Removing the circlip from the end allows the damaged part to be removed:

Sturmey pic

A number of gear fragments fell out at this point. One of the planet gears was missing, with just the pin remaining.

Sturmey pic

Leaving that for now, we can continue to disassemble: the various stages of the transmission simply pull off the axle:

Sturmey pic

The largest stage, all greasy. The grease was mostly pretty clean still.

Sturmey pic

Each stage has three freewheel pawls on its outside, which engage with a ratchet ring at the back of the previous stage.

Sturmey pic

Looking at the axle with some stages removed, we start to get an idea of how the shifting works:

Sturmey pic

There are three wee spring-loaded shifter levers, recessed into the axle, and controlled by the three rings on the other end. When raised, the levers engage with the splined bore of the planet gears rather like the pawl of a freewheel:

Sturmey pic

Removing a circlip lets the controller rings slide off. These have a cam-like profile, which clearly controls the shifting sequence:

Sturmey pic

The shifter levers can now drop out:

Sturmey pic

And all three posing for the camera:

Sturmey pic

At this point it's about as disassembled as I can go. The 'stages' seem to be press-fitted together from two main parts, holding the 'sun' and 'planet' gears within. So after a little cleaning just time for an exploded pic:

Sturmey pic

Click here for a full-size (3000 pixels wide, 300k) version


Another pic of some of the gears:

Sturmey pic

And now I'll put it back together, just to prove I can :-)

As this is a non-working hub I've not regreased before reassembly.

First get all those wee springs and shifter levers back in place, slide on the controller rings (they're coded A B and C), slide all the controller rings back onto the axle, and secure with the circlip.

Reassemble the pawls and spings onto the gear units. Then slide the gear units back on:

Sturmey pic

Don't forget this shield thingy which goes on before the first gear set:

Sturmey pic

Fit the final freewheel pawls and replace the circlip and the innards unit is now complete:

Sturmey pic

Refit the axle bearing cone:

Sturmey pic

and replace remaining drum brake parts:

Sturmey pic

Now flip the hub back over, and screw the big bearing ring into the hub shell:

Sturmey pic

Add the bearing race, and settle the next bit in place:

Sturmey pic

The bit with the two 'prongs' sticking up engages with the 'controller rings' which handle gear shifting:

Sturmey pic

Those prongs engage through to the cable drum, now fitted along with the plastic shield for the outer bearing race:

Sturmey pic

Just a few spacers to go:

Sturmey pic

Add the shift cable support plate, washer and circlip:

Sturmey pic

and it's done!

Sturmey pic


Posted by Ben - Kinetics (ben@kinetics-online.co.uk) on Wednesday 2 Aug 2006
Show off ;-)

It's good to see that Sun Race SA are serious about product development, though - they're obviously interested in building a quality hub.

One small comment: The Rohloff will always feel less slick because, uniquely, it has the gear indexing in the hub and not the shifter. This is a good thing, as it means the hub is always in gear - unlike other systems which can feel ike they're in gear when they're not ;-)

 
Posted by Tom (Velovole@hotmail.com) on Wednesday 2 Aug 2006
You ARE enjoying your post-issue playing aren't you? :-)

C'mon then: Rohloff next! (Exit, persued by a bear...)

 
Posted by Peter Eland (Peter@velovision etc) on Wednesday 2 Aug 2006
Well it was more fun than the VAT return, which is what I'm doing now :-(

If someone would like to provide a Rohloff I would be delighted to take it apart and put it back together again, assuming of course that I can keep it afterwards :-)

 
Posted by Becky (me@home) on Wednesday 2 Aug 2006
How long Ben did you say it took someone? Three hours?

 
Posted by Ben - Kinetics (ben@kinetics-online.co.uk) on Wednesday 2 Aug 2006
Months! It was three months I heard. though they could have been a bit ham-fisted, and doing it without instructions.
I've taken apart all the bits you'd ever need to - swapping from clickbox to internal routing, swapping end plates, replacing gaskets, all that kind of stuff. I've got an exploded diagram over my desk which is scary ;-)

 
Posted by Bernhard Kuehn (bernhardkuehn@yahoo.de) on Friday 15 May 2009
For my Eight speed hub Type XRF8 I need a fulcrum lever (HSJ 3810.0110.002) for my bicycle frame with non horizontal dropouts (ca. 60 degree).Where can I buy it?
many regards Bernhard Kühn

 

 
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