Re: Half-step on Sturmey, was [CR]How to build up this Hetchins?

(Example: Framebuilders)

Date: Thu, 18 Sep 2008 22:49:00 -0500
To: <classicrendezvous@bikelist.org>
From: "Mark Stonich" <mark@bikesmithdesign.com>
Subject: Re: Half-step on Sturmey, was [CR]How to build up this Hetchins?
In-Reply-To: <BAY129-W460D3EBC26FF34315B1F07FE4E0@phx.gbl>
References: <48CE3D89.9060804@verizon.net> <1262235490.20080915123431@rogers.com> <E1KfIj8-0004Zh-U3@elasmtp-spurfowl.atl.sa.earthlink.net>


At 07:58 PM 9/18/2008, Tony Colegrave wrote:
> Regarding 'hybrid gearing', in my experience the use of 'dished' spro
>ckets back-to-back will usually work O.K., but I don't think that the lar
>ger sprockets (which tend to work best) were 'dished'?

Yes the SA cogs of 16t and larger were dished. However the tooth profile of the SA 22t was rather odd and allowed the chain to skip when used with a derailleur. Fortunately a local wholesaler had a bunch of 22t Shimano 1/8" cogs back in the '70s and they weren't selling so I bought the lot for a song. Still have one somewhere.
>Also, AFAIK, the
>se sprockets were only made for 1/8" chain and will not 'work' with 3/32" c
>hain - unless they're 'skimmed down', of course. If you're going to use a
> 1/8" chain, you'll need to be sure that the derailleur mechanism is able
> to accept this width (most early ones will, obviously) and be careful to
> choose as 'narrow' a chain as possible (rivet lengths in 1/8" chains seem
>to vary considerably).

Modern 1/8" chains from SRAM and KMC have an overall width less than 3/32" chains of a few decades ago. They will work in almost any old derailleur. "Back in the day" we'd add thin washers on either side of the idler and jockey wheels.

Modern Shimano and SRAM hub gear cogs fit either 3/32" or 1/8" chains but are stamped in such a way that they take up 1/8" on the driver.

At 07:39 PM 9/18/2008, Harvey Sachs wrote:
>BUT, with standard S/A cogs, I would expect the shifting across the
>external cogs to be pretty cruddy unless you grind off the tips like
>more modern cogs on FW. Like 60s stuff.
>
>Your mileage may vary, of course.

This isn't really necessary, shifting is pretty good.

For perfect shifting or to get larger cogs I use a modified 7 speed Shimano Cassette cog (pre-Hyperglide when possible) for the inner cog, then a 1mm freewheel/fixed cup spacer then a dished small cog. http://bikesmithdesign.com/SA/2Cogs2.jpg http://bikesmithdesign.com/SA/2Cogs.jpg http://bikesmithdesign.com/SA/CogMod.jpg shows how the cassette cog splines are altered.

When Jane was recovering from a knee injury I put a 22-34 pair on her SA 5 speed hub. Her Huret Duopar shifted them as smooth as butter. http://bikesmithdesign.com/SA/22-34.jpg
>I have seen 3 cogs on a threaded driver, but it was a long time ago.
>I think those were part of a factory Cyclo conversion kit that
>included the derailleur, shift lever, and cable set.

The Cyclo kit fits the 3 spline driver. I imagine earlier kits fit threaded drivers.

Mark Stonich;
     BikeSmith Design & Fabrication
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