Mark Stonich wrote:
>Shimao Nexus cogs work fine with 3/32" or 1/8" chain. I buy the
>22s, 10 at a time for friends and family.
Those are good, but we actually sell a lot more of the SRAM 24 tooth
sprockets, which also work for both types of chains.
>I always found the ratios of the AW 3 speed to be a bit too wide. I
>find the range and ratio jumps of the 5 speeds to be the perfect
>compromise.
I've toyed with the idea of making a close/medium ratio 3-speed from
an S5 or FW by removing some of the internal parts. I suspect this
could improve the efficiency, if one didn't need the range.
>You can put the guts of any pre April 1984 5 speed into any pre
>April 1984 AW or FW shell.
What happened in '84? All of my Sturmey-Archer hacking has been with older models.
By the way, almost all of the parts of an S5 are interchangeable with
FW. I used to regularly convert FWs into S5s.
>For shifters you can use an AW shifter on the right and another on
>the left, or better yet a friction bar end or thumb shifter.
MUCH BETTER YET with a friction shifter on the left.
>
>S5s had a bellcrank and a pushrod. The early bellcranks were quite
>horrid things bent from sheet metal. Later ones are very nice
>indeed. I've seen later, NOS ones go for $40 on ebay, more than
>I've ever paid for a steel shelled NOS 5 speed hub. I'm set up to
>tap Shimano bellcranks to fit Sturmey axles, but the leverage is
>different, so you can't use them with an SA shifter on the left.
>http://bikesmithdesign.com/SA/bellcranks.jpg
You REALLY don't want to use an SA shifter on the left.
>The upside of the S5 is that the left cable is slack, and no springs
>are compressed when you are in medium ratio mode, which is most of
>the time.
It is my impression that S5s generally have less internal friction.
>
>The downside is that you pull the cable of mesh the square ended
>dogs when shifting to wide ratio mode. If the ends of the dogs butt
>against the other, the cable stops moving, and you are left in a
>false neutral. Careful shifting will eliminate this as a problem,
>but I'm not always careful.
The key to this is to only shift the left side
_while_pedaling_forwards_. They work quite smoothly if you do this.
>So I add a spring between the bellcrank and the threaded adjusting
>rod, as shown on the Shimano bellcrank in the photo. With the
>spring, the cable keeps moving if the dog ends butt against one
>another, and the shift is completed as soon as one moves.
One used to be able to buy cable anchorages with a built-in spring.
These were great for this application, also for using as a
"pre-selector" for the right side cable.
>
>S5/1 & S5/2 The upside is that since you pull the dogs out of
>engagement, instead of pushing them together, the shifting problem
>won't occur.
>
>The downside is that there is a bit of extra drag, and spring that
>does engage the dogs is almost always compressed. So unless it's
>made from very good stuff, I expect it will eventually lose pressure.
I don't believe that's correct. Springs don't "lose pressure" unless
they are extended/compressed past the yield point.
>FW
>The problem with the FW 4 speeds is that it takes quite a bit of
>cable tension to engage low gear against the extra springs, which
>can sometimes overpower a worn shifter. Another is that the
>indicator rods are rare and delicate. Also shifters are harder to
>find.
Those are some of the main reasons for upgrading them to 5-speed.
>OTOH the 5 speeds use common parts. AW shifter, at least on the
>right. An AW indicator chain can be used on an S5/1 or 2, and you
>can make an S5 pushrod out of a nail. In fact I prefer the nail to
>the stock pushrod.
Yep.
>The extra gear on top allows you to add a couple of teeth on the
>rear, for a bit of help on the hills.
Yep.
I have a bunch of technical/historical material on my Web site about
older British bikes. See:
http://sheldonbrown.com/
Sheldon "Epicyclic" Brown
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