Just bought my fifth Sturmey-Archer AM

[rogerzilla]

I love these hubs - three really usable gears and neater than a derailleur setup. Make normal gear 60" and you can get up most hills in the low gear (it's equivalent to 42 x 21 on a derailleur bike). They are super-smooth and efficient.

They all benefit from being hybridised with an AW (pre-NIG) since the AM 2-piece indicator tends to unscrew itself in use and the shells are usually 40h. I tend to just use the AM planetary gears and everything else is AW. The two hubs were designed together in the 1930s by William Brown so parts are amazingly interchangeable.

95% (at least) of AM axles are only 146mm which is ideal for 110-115mm spacing. 160mm axles are very rare but allow up to 126mm spacing; more if you have reasonably thin dropouts. You need 10mm sticking out on each side; 2mm for the anti-rotation washers and 8mm for the axle nuts. 8mm doesn't sound like enough for an interrupted thread but that's how thick a SA left-hand nut is, so I know it's fine. A torque wrench is essential - 25Nm, 20Nm if you can get away with it.

Pics as I take the hubs apart and build the new chimera. Oh, and it's going in the Moulton TSR.

http://www.sturmey-archerheritage.com/index.php?page=history-detail&id=52

Best to avoid the 1930s AM hubs - the gear ring has discontinuous dogs which engage the clutch and is prone to slipping in normal gear. The 1950s hubs have splines instead and never slip.

 

[simongt]

I've been using a Sturmey 5 speed for several years after going thru umpteen derailleur sets. For my general commuting, a reliable 'fit & forget' type of gearing; chain always in line, weatherproof. Job done - !

 

[rogerzilla]

Ah, you need to try an AM. Only three speeds, but the *right* three speeds!

 

[SkipdiverJohn]

Ah, you need to try an AM. Only three speeds, but the *right* three speeds!

Don't you like the AW then? I love the simplicity of Sturmeys but I've only ever ridden the AW/AG, the FW, and a Styria AW clone on a Puch.
I must admit though, I think SA gears would be better if the reduction was 33% and the overdrive 25%, rather than the other way round. 3rd is often a bit high except with a tailwind.

 

[rogerzilla]

20210326_134627 by rogerzilla, on Flickr

AM hub, alloy 40-hole shell, standard axle

20210326_134642 by rogerzilla, on Flickr

NOS AW (it has the factory protective grease on it!)

20210326_134728 by rogerzilla, on Flickr

Two AM axles. The long 6 1/4"/160mm one is super-rare. Note the sun gear is machined onto the axle because it's so much smaller than the replaceable one on an AW.

The alloy AM shell is about 4oz/113g lighter than a steel one but the dimensions are identical, so the flanges are really too thin for alloy! The current SA alloy shell for the SRF3 is usable if drilled for an oil port (I did this on my AM-equipped Brompton) but it offers no weight saving over a steel shell.

Next job is to open them up. The AW is easy as I have the right tool and it's never been ridden. The AM will be tricky. The square-dogged ball ring spanner is unobtanium these days, so it has to be a punch. It'll be well torqued down by pedalling. Oh, and it's not built into a wheel. Fear not, I'm good at this...

 

[rogerzilla]

Don't you like the AW then? I love the simplicity of Sturmeys but I've only ever ridden the AW/AG, the FW, and a Styria AW clone on a Puch.
I must admit though, I think SA gears would be better if the reduction was 33% and the overdrive 25%, rather than the other way round. 3rd is often a bit high except with a tailwind.

AW is fine but I find I rarely use low gear. I rode an SRC3 to work for 8 years.

The reduction and increase have to be that way round in a one-stage epicyclic. The hub's ratio is merely the sun teeth added to the gear ring teeth, divided by the gear ring teeth. This happens to be 1.33:1.

The AM is not as simple. It uses compound (stepped) planets which give the effect of a much bigger gear ring and (with the smaller sun) a closer ratio. To get even closer ratios in the AC or AR requires multi-stage epicyclics, which are less efficient.

 

[rogerzilla]

20210326_164236 by rogerzilla, on Flickr

Not too difficult. The AW, predictably, came apart with finger pressure.

How cheap were SA to change from 8 ball retainers to 7 ball retainers?

It all needs a good clean up, then I'll post a photo of the bits. Then to build a frankenhub around the longer axle that has an AM epicyclic but AW other bits. Gets rid of the 40h issue and the unreliable AM indicator arrangement.

You can see one end of the three AM compound planets. The end of the planet with the big gear meshes with the sun and the end with the small gear, which you can't see yet, meshes with the gear ring. The sun and the gear ring are not in the same plane. Oh, and the planets have to be "timed"...

 

[SkipdiverJohn]

Some excellent explanatory pictures there @rogerzilla.

 

[rogerzilla]

All in bits. The critical bits of the AM are very good and it looks like it has very little mileage on it (the internal plain bearing surfaces are minimally worn - sometimes there is a wide polished wear track between all the parts and the hub is insufferably rattly!).

The axle bearings (cones, driver, LH ball cup) aren't perfect, with a little pitting, so I'll use AW parts there. The RH ball ring with the 24 x 3/16" race is perfect so I will reuse that.

The axle key is round rather than the usual square item. I haven't looked to see if it's threaded or plain yet. If the former, someone did the AW toggle conversion previously!

Most tedious bit: cleaning out the ball retainers. You can't get the 8 ball type any more, so they are worth saving. Obviously I'll use new balls throughout. It is impossible to assemble an SA hub without the retainers unless you stick the balls in place with grease, which is a real no-no.

The alloy shell will be a useful spare as I have a wheel built around the same shell type, and one day the flanges will crack. Getting the LH ball cup off this one could be a challenge when it's not in a wheel. I might need to rig up some sort of pinboard to hold the shell while I unscrew the cup (it's a LH thread, otherwise it would undo itself in low gear, when drive side is the left).

 

[rogerzilla]

20210328_193931 by rogerzilla, on Flickr

Bits ready for reassembly.

 

[rogerzilla]

The clutch on an AM engages with proper dogs on the planet cage, not just the ends of the planet pins as on the AW. This means it doesn't slip out of high gear, which is possible with a worn AW.

20210328_193947 by rogerzilla, on Flickr

 

[rogerzilla]

I reused the AM ball retainers with new balls, but used the AW dustcaps. These dustcaps are a press fit and there is a technique to getting them out without bending them.

20210328_194014 by rogerzilla, on Flickr

 

[rogerzilla]

The "R" springs for the pawls are cheap and I always replace them. The pawls are very lightly sprung on an SA hub, which is why grease is a bad thing. The special SA grease is more like a very thick brown oil but I prefer to only use oil. It means the hub should never need opening again, whereas grease condemns you to regular overhauls to remove the contaminated grease.
20210328_194004 by rogerzilla, on Flickr

 

[rogerzilla]

Lots of spacers to get it to 130mm, which the designers never envisaged. There is enough axle for the dropouts, antirotation washers and axle nuts. Just. The axle shouldn't bend as SA make hubs in 135mm spacing with this shell!

20210329_074640 by rogerzilla, on Flickr

 

[rogerzilla]

So...planet timing. Because the planets mesh with the sun and the gear ring separately, they only do this properly if they are set in the correct starting position relative to each other. It's a bit like setting TDC and camshaft timing on a combustion engine.

The planets have small "I" engravings on the inner face of the larger cog. On all three planets, the three "I" marks must face directly outwards (or directly inwards) at the same time. Fitting the gear ring then locks them all in the correct phase with each other.

The hub will work if this is not done, but it will be completely ruined after a few miles.