Author Topic: Rogerzilla's £40 Sturmey-Archer ASC thread (Read 8796 times)

rogerzilla · « **on:** 18 April, 2013, 04:54:13 pm »

It's here and it's complete with the indicator and toggle. It even works when I put it in the wheel jig and turn the sprocket. LH ball cup looks good although at some point an extra oiler has been added to it (could be filled as the cup will benefit from some silver paint anyway). Pics later. It is absolutely nothing like an S3X inside; there are two sets of planetary gears and it uses them in series. Fascinating piece of clockwork.

clarion · « **Reply #1 on:** 18 April, 2013, 04:55:17 pm »

Interesting that it's a different mechanism. I wonder why the S3X didn't repeat the design?

rogerzilla · « **Reply #2 on:** 18 April, 2013, 05:28:46 pm »

The S3X is probably more efficient as it only ever uses one planetary gear at a time (both would be equally efficient in top gear). However, the ASC cannot slip in the same way as the S3X; there are "no drive" positions but the suns aren't locked by tiny little sliding dogs.

I believe the ASC is a hack of the AC or AR, which was already a four speed modified into a 3- speed to get closer ratios. The ASC gives 10% and 25% reductions whereas the S3X gives 25% and 37.5%.

You can't get an ASC into rear spacing greater than 120mm, and you need fairly thin steel plate droputs to achieve that. The axle is only 5 3/4" long. The S3X is therefore better for modern frames.

At the moment the only thing it seems to *need* is a new shell due to the cracked flange, although I'll replace all the bearing balls. Like the S3X, there is not a pawl or pawl spring anywhere. Derek at Old Bike Trader is trying to get me a current 36 hole SRF3 alloy shell.

rogerzilla · « **Reply #3 on:** 18 April, 2013, 06:16:53 pm »

Straight out of the packet:

The legend:

Opened up (these hubs, like the S3X, don't screw themselves up tightly in use so dismantling is a breeze)

Lots and lots of cogs

Why it was cheap (and the seller didn't advertise it as an ASC)

The left hand ball ring (which needs tio be pressed into a new shell). Includes the secondary annulus and the dogs that transmit drive from the internals to the shell.

rogerzilla · « **Reply #4 on:** 18 April, 2013, 06:23:12 pm »

Sheldon Brown on the ASC: http://sheldonbrown.com/asc.html

Hilary Stone on the ASC (he has a NOS one with shifter for £450 if you're interested): http://www.classiclightweights.co.uk/designs/hsasc.html

The special ASC shifters are widely available if you find Lord Lucan, who apparently has the remaining supply. Other people just use a 4-speed shifter and ignore the "3" position, or file off the detent so the trigger flicks straight between "2" and "4". An S3X shifter would sort of work but wouldn't quite click into "1" (it pulls slightly too much cable, whereas the normal 3-speed shifter pulls too little) and you'd have to rely on friction to hold it there.

rogerzilla · « **Reply #5 on:** 18 April, 2013, 08:46:06 pm »

Now reduced to a box of bits. All very good; the only missing part, oddly, was the RH axle ball cage. The driver appears to be an unused part, so I suspect the original was nicked for something else. Since Hilary Stone has a stock of 12-spline SA racing sprockets, I'll probably fit that 12-spline driver I've had kicking around.

I think the only new internal parts I need are ball cages, dust caps and a locktab washer, so that's about a fiver's worth. This hub has been looked after by previous owners, to the extent that they added extra lubrication. The only challenge is going to be knocking the ball cup out of the cracked shell; Sutherland's suggests supporting the flange on blocks of wood and "pounding" out the cup using a hammer and another piece of wood. Very high-tech. I reckon heating it up in the oven will make the job much easier, since the alloy shell will expand much more than the steel cup.

DrMekon · « **Reply #6 on:** 19 April, 2013, 07:24:33 am »

I've enjoyed reading this. Sounds like a lovely piece of kit.

rogerzilla · « **Reply #7 on:** 19 April, 2013, 08:14:55 pm »

The Sutherland's technique for removing the left cup from the cracked shell doesn't actually work. The flanges bend but the cup doesn't shift at all, even when heated to about 150 deg C in the oven (which should expand the shell far more than the steel cup).

I think I'll saw the shell long ways and try to split it.

What worries me is that I'll also need to get the left cup out of an new SRF3 shell *without damaging the shell*, since the shell isn't available on its own, only with the cup already pressed in. I might let someone else do that.

rogerzilla · « **Reply #8 on:** 20 April, 2013, 11:10:30 am »

Ta da!

And here's the complete hub, minus only the shell (which will come from a current model)

And I can finally use the funky 12-spline driver (marked "FOR RACING" on the parts diagram) with left-threaded lockring, since Hilary Stone has some of the 12-spline sprockets.

rogerzilla · « **Reply #9 on:** 20 April, 2013, 07:09:15 pm »

Update on the oiler in the LH cup: it may be original, or at least a common modification. There's a photo of an FM with the same feature here:

http://www.classiclightweights.co.uk/sa-maintenance-blakeley-rest.html

Note that these FM cups are all screw-in; the ASC was the first press-fit cup (all Sturmey hubs have had press-fit left cups since the 1960s, which is why this one can easily go into a brand new shell). Why decide on a press fit for the ASC? Well, otherwise it would unscrew itself during leg-braking

rogerzilla · « **Reply #10 on:** 05 May, 2013, 09:02:29 pm »

Given up on the 12-spline sprockets, since Hilary Stone is useless. It was shipped new with a normal 3-spline driver most of the time, anyway.

A new XRF5 hub shell (high flange) is on its way and I have some NOS plastic oilers from Greece, of all places, so I can drill and tap the shell for one. The indicator rod on the left turned out to be an FW one (useless as it won't make the ASC work at all; the bit between the two clutch keys is the wrong length) but amazingly I managed to find a real one for sale, at a reasonable price.

The trigger was very easy to dismantle and I'll modify it using my f-i-l's bench grinder in two weeks' time (a file just bounces off the hardened steel ratchet). Infamously, the ASC uses a totally unique cable pull.

rogerzilla · « **Reply #11 on:** 05 May, 2013, 09:13:17 pm »

HOW IT WORKS

Low gear and high gear are simple; middle gear is rather strange.

There are two epicyclics.

The primary one is near the centre of the hub and has the same size sun, planets and gear ring as the common AW. The primary planet cage is splined to the left ball cup (which is pressed into the shell) and all drive goes via it.

The secondary epicyclic is in the left ball cup and has a large sun and small planets. The secondary gear ring is machined into the left ball cup.

The primary sun can be clutched (by means of a "dog ring" to either the axle or to the secondary planet cage.

HIGH GEAR

The driver (which carries the sprocket) is clutched to the primary planet cage, the same as with high gear in an AW. This means that the shell turns at the same speed as the sprocket (direct drive). The epicyclics play no part.

LOW GEAR

The driver is clutched to the primary gear ring. The primary sun is clutched to the axle. This makes the primary planet cage, and hence the shell, turn 25% more slowly than the gear ring. This is, again, the same as an AW.

MIDDLE GEAR

This uses the same principle as low gear BUT the primary sun is declutched from the axle and instead clutched to the secondary planet cage. This allows the primary sun to rotate in the same direction as the sprocket, at a speed governed by the secondary epicyclic mechanism. The slowly-rotating primary sun gives the effect of a much larger sun and hence makes the gear ratio closer. The net effect is a reduction of 10% from direct drive.

The ASC is not a "cascade" gear, where the output from one epicyclic feeds the next, leading to a multiple drop in efficiency. The secondary epicyclic is not transmitting power and is really just a kind of escapement to control the rotation of the primary sun. This means that, although middle gear should be the least efficient, it is not much less efficient than low gear (about 3-5% loss).

therealrendo · « **Reply #12 on:** 21 May, 2013, 12:34:17 pm »

Hi

Watching this with interest.

I have an ASC hub, which is in need of service as i only have 2 gears. i've had the hub open and i reckon i have a washer missing. i wonder if you can confirm if you have one in yours and if you could maybe measure it. its not available on any spare parts so i might need to buy something generic.

If you dont mind i'll reply again with the part number, and if you need any help with putting that box of bits together or any photos i'll be glad to assist if i can.

rogerzilla · « **Reply #13 on:** 21 May, 2013, 01:01:01 pm »

Is it the large locating plate under the three small planets, or the lockwasher for the nut that holds that plate in place? The latter is a readily available spare.

therealrendo · « **Reply #14 on:** 21 May, 2013, 01:36:03 pm »

Actually i have two parts missing, one of them is the lockwasher which i have found on the oldbiketrader website, the other is called the thrust washer, part K411. i'm not even sure its necessary as the clutch spring sits nicely in the recess of the thrust ring.

rogerzilla · « **Reply #15 on:** 23 May, 2013, 06:39:55 am »

Mine didn't have a thrust washer, and has never been apart. They are only fitted to hubs of certain ages.

rogerzilla · « **Reply #16 on:** 26 May, 2013, 09:04:01 pm »

The shifter ratchet and lever on a beaten-up 4 speed trigger have now been ground away to give the required extra cable pull between top and middle gear. Just needs a little tidying and undercutting with a small file.

I also sprayed the left hand ball cup with silver Hammerite, which is a pretty good match to factory original.

clarion · « **Reply #17 on:** 26 May, 2013, 10:07:11 pm »

Excellent. This is very exciting.

rogerzilla · « **Reply #18 on:** 27 May, 2013, 11:27:21 am »

Trigger now modified with a little undercut to preclude any slipping. It pulls exactly the correct amount of cable to get from H to N now. I think it might pull slightly too much to get from N to L (that's not modified by the grinding and is left "as is"), but we'll see. I'm trusting Jim Gill, who wrote the instructions on Tony Hadland's website. This mod, which basically causes it to "overshift" from N to H, is a more sophisticated mod than the usual method of taking a 4 speed shifter and grinding off the "3" (or "N") detent completely so the shifter goes 1, 2, 4. That works but the cable pull isn't quite ASC specification.

Still need a shell (Derek at Old Bike Trader is working on something, but that's the least of my worries since anything made since about 1970 will do) but then it can be built into a wheel and tested. The internals are really, really good and show no signs of wear.

Toady · « **Reply #19 on:** 28 May, 2013, 10:38:22 pm »

I don't ride a fixie and I haven't ridden a SA hub gear since my paper round, but I've found this thread absolutely fascinating. Thanks RZ

rogerzilla · « **Reply #20 on:** 09 June, 2013, 08:53:58 pm »

Not much of an update this week, but I have a suitably plain silver 36h rim for the hub. Slightly shop soiled (you can't tell) from J E James Cycles, a tenner. Still don't have a shell; Derek has offered me a threaded one, a S3X one and various other useless options. What I actually want is a current SRF3 3-speed shell with the left cup knocked out, but SA only sell the 28h shell as a spare part

I could just buy a clean 70s or 80s AW from fleaBay, but I don't really want a steel shell because the thin flanges mean you need fiddly little 2mm washers under modern spoke heads, and an ASC deserves an alloy shell anyway.

I might have to buy a new 36h SRF3 (£70) and flog the internals to get some of the cost back. Most people need the mechanism to fix their bike, not the shell.

rogerzilla · « **Reply #21 on:** 22 June, 2013, 10:59:38 am »

A 36h shell is now on the way. I'm not sure how to press in the left cup yet; I could either use a vice and blocks of wood or (more fun, and considerably more powerful) a hydraulic car jack and the garden bench with everyone sitting on it. Or even a car - that should give a good half ton. Or do it the boring way with a mallet.

rogerzilla · « **Reply #22 on:** 24 June, 2013, 12:46:33 pm »

The shell is here and ironically it's from an S3X. Dimensions haven't changed over the years so the ASC should go straight in. Needs an oiler adding first (M6 tapping is good enough for the Sturmey plastic oil cap).

A trial fit shows that the dimensions of an S3X shell are identical to all Sturmey A-series shells since.1936 and the LH cup looks as if it will be a good firm press-fit. Derek at Old Bike Trader informs me that the S3X left cup, when it came out of this shell, wasn't actually splined and the inside of the shell is indeed unmarked. The new ones rely totally on the interference fit to prevent rotation, whereas the old ones (see upthread) are toothed to bite into the shell.

rogerzilla · « **Reply #23 on:** 24 June, 2013, 09:55:12 pm »

It's together. It took a 4 lb lump hammer, all my strength and a lot of blocks of wood (they kept splitting) to press in the left cup. No way that is ever moving, especially as I used flange sealant to make it oil tight.

It is very, very smooth in all 3 gears. Better than an FW by miles. I would say there is less lash than in the S3X.

Now I need to build it into a wheel and see how well the shifter works.

rogerzilla · « **Reply #24 on:** 29 June, 2013, 06:48:08 pm »

Wheel laced and half-tight. It might make it onto the road tomorrow. The clubman will just need a couple of links taking out of the chain (it has a 40T chainring, so the ASC will need a 15T to give a 70" direct drive) and a shifter swap; as it already has an SA hub, the fulcrum clip, roller and cable are already there.

Will it shift? Will it slip in the two lower gears? Will it just be a very heavy and rather sloppy 70" fixie? We'll see.

Author Topic: Rogerzilla's £40 Sturmey-Archer ASC thread (Read 8796 times)

Toady