Wednesday, 20 July 2016

Sturmey Archer AW3 Gear Hub Strip and Rebuild

I've been having fun rebuilding the internal gear hub on my commuter bike.

Meet "Frank The Tank".

He is called Frank the Tank because he's a Frankenstein of new and second hand bike parts from lots of places and because he's no lightweight ;) I built him up from parts scavenged from five different donor bikes and a few new parts too.

He's based on an old Raleigh steel frame that someone had stripped and powder coated in white for a project before losing interest and selling it on eBay. Unfortunately the elegant white 1" threaded fork that came with it used the old 26TPI thread standard and I couldn't find a replacement headset for it at a reasonable price so a new black fork was chosen. He's been built to be an all weather, low service reliable bike for commuting and shopping.

Part of the reliability / simplicity was to choose an internal gear hub. Three speeds is just enough for the hills around here and fully built rear wheels with Sturmey Archer AW3 gear hubs are available on the internet for quite reasonable prices. Sure the rims are heavy but they've stayed true despite the abuse!

I've used him on my commute to work for a couple of years now in all weathers and, having survived two winters of commuting, it was time for a strip down and clean, including the gear hub. What started as a quick "I'll just regrease the bearings and adjust the cones" turned into a full on strip, clean and re-oil and re-grease of the entire hub with me learning a lot about it on the way!

Sturmey Archer hubs

I've been generally very impressed with the quality of the AW3 hub. Everything is nicely machined and has stood up to 2000 miles of abuse with zero maintenance and hardly any adjustment. The history of Sturmey Archer is well documented on the Sturmey Archer Heritage site with old engineering drawings and adverts. There's even a Dutch picture from 1958 showing how the 3 speed mechanism works.

Advert for the Sturmey Archer / Raleigh 3 speed hub
Yorkshire Post, 1903. (C) Sturmey Archer Heritage
It is particularly impressive that the predecessor to the Type AW hub that I own was originally designed in 1914. Externally there is very little difference and internally there only appear to be minor changes between the 1914 version and the modern version. Most satisfactory.

L: 1914-1916 Type A hub
R: 1936-2001 Type AW3 hub

There's an amusing anecdote on the continuing production of Sturmey Archer hubs by the Taiwanese firm Sun Race on (all hail) Sheldon Brown's website
I heard an interesting anecdote from a Sturmey-Archer veteran employee, now with SunRace/Sturmey-Archer:
Back in the day, sometimes a batch of internal parts would be just a bit out of tolerance, maybe a bit too small, or a bit too large, whatever. The production people would take a sample to the engineering department, where a grey-haired engineer would check it out and often say "Well, it is a bit out of spec, but not really enough to cause failure, so let's let it go."
SunRace didn't have those engineers who had grown up with Sturmey-Archer in their blood, so when they found a batch of out-of-spec parts, they would say "That's out of spec! Melt it down, and make new ones, and do it right this time!"

Strip, Clean and Rebuild

Any numbers in brackets refer to the component in the exploded diagram / parts list.

Removing the screw in ball ring (13) was the hardest part of the process. This part has a series of inner ramps that the drive assembly (15) pawls engage in. So me standing on the pedals for the last umpteen hundred miles meant it was tighter than Gary Barlow's wallet. It looked like it needed a special tool to remove so I cut out a section of 3mm aluminium plate to fit the dents around the rim. However it was that fast in place that it just chewed up the plate when I attempted to use it to unscrew it.

I had considered using a screwdriver and a hammer to drift it round but thought that was excessive until I did some internet research and found a couple of pages and a video that all recommended doing that very thing. The official instructions say to either use a C-spanner or a hammer and punch! Sure enough it loosened it off nicely, the hardened steel of the ball ring shrugging off any damage from the much softer steel of my largest, cheapest flat bladed screwdriver.

Unfortunately the time between initial disassembly and me managing to get the ball ring off meant that I'd forgotten the order of the parts so far. So I just dumped them all into a big tub full of hot soapy water, gave them a clean and a dry and then tried to figure out which bit went where.

There was precious little oil in the hub and only a small amount of good grease. There was a fair amount of crufty horrible grease on the gear ring assembly and the drive pawls and the grease in the bearings was pretty much non existent. Definitely due a service then!

AW3 hub internals, cleaned and disorganised!
With a bit of tinkering and a pale ale or two I figured out what went where. I was most impressed with the solid feel of the hub as I rebuilt it and the engineering processes that must have gone in to developing and making it. The axle (27) is a nicely machined part with a slot for the gear selector / axle key (28) and a coaxial hole down one end for the selector chain (32).

The fiddliest part of the build is assembling the gear ring assembly (9) and the associated pawls and pawl springs. The springs are really fine and I've dropped them at least three times and had to go hunting on the floor for them conducting a finger tip search with a flashlight and a magnet.

I'd had a few goes at fitting everything together and eventually figured it out before getting all the parts laid out in order.

The assembly from here is a dry run prior to things being greased and oiled for the final assembly.

All fine up to this point but this is where I went wrong. The black plastic dust cap is meant to be fitted after the drive mechanism and cone have been screwed on. Otherwise when you tighten the cone it tries to compress the dust cap between the cone and the bearings and the whole thing seizes up. To my credit, I got this far without referring to the manual or the diagrams! Maybe I should have referred to it sooner ;)

The next thing to do was to grease it all up using white lithium grease throughout. Mistake. Error. Redo From Start+++++. Putting grease on the freewheel or drive mechanism pawls just causes them to stick to their carrier and not click back into place - the main function of a pawl. As a result it took about 5 seconds for the freewheel or the drive mechanism to click into place. Cue a re-strip and re-clean, applying nothing but light cycle oil to all of the internal components and grease to all three bearing races. Much better!

Putting it back on the bike

Upon reassembly the freewheel seemed to jam so my first thoughts were that I'd put some pawls in the wrong way round also I couldn't figure out why tightening the cones didn't stop a significant amount of wobble at the rim.

This was when, after looking at the exploded diagram that I figured out that I'd put the dust cap on in between the bearing surfaces rather than covering the drive mechanism. Idiot. I'd also put the non drive side spacer washer (25) on the outside of the lock nut and not the inside (minor error).

Lastly I realised I'd lost the non drive side axle nut so had to order a new one from the eBay store of Hopkinson Cycles in Horbury. More idiocy on my part.

I corrected these issues, had the usual round of faffing around trying to adjust the cone bearings so that they were juuuuuuust right and presto! the wheel was back in and working properly. Nice sharp clicks from the drive and freewheel pawls, smooth changing of the gears, lovely. I'll feed it some oil down the changer hole so it has something to be getting on with and away we go  :)

Further Frank-ing About

I also took the time to fit the proper diameter seatpost. I'd been using a 1" seatpost with some shims made from a coke can which meant a real fiddle adjusting saddle position, the very thing that had caused me a bit of knee pain beforehand.

After measuring up I ordered a 27.0mm seatpost (not the conventional 27.2 of modern bikes) from eBay and a nicer brown saddle I'd taken off the tandem, which is much more in keeping with the look of the bike.

I also improved the pannier mounting, removing the crappy looking P-clips and replacing it with a much nicer piece of threaded rod and some nuts between the original rack mount brackets. This moved the mounting point inboard to suit the rack I've got and it tidies up the frame too.

This means that Frank is ready for the next 2000 miles of urban pottering, commuting, shopping and general practicality.

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