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 Post subject: Sturmey Archer FM 4speed
PostPosted: Mon Jan 10, 2011 11:10 am 
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Anyone know what these are like to ride with? Sheldon Brown lists it as a medium ratio 4 speed....


Ive just dug one out of my stash of hubs with some other bits while clearing my shed out in search of somthing else...

Didnt even know i had it.

Im guessing medium ratio meaning its just going to be like an AW but with a higher first?


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PostPosted: Mon Jan 10, 2011 3:05 pm 
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retrowagen1234 wrote:
Anyone know what these are like to ride with? Sheldon Brown lists it as a medium ratio 4 speed....

It's a nice hub. If you set direct to about 70" you get three decent cruising gears and a climbing gear. I had one on my old Mercian for a while. The indicator rods are fragile and hard to get though, so take care of yours if it's present. Mine's in line for a long-awaited rebuild into a steel shell.

Quote:
I'm guessing medium ratio meaning its just going to be like an AW but with a higher first?

No, they're quite a bit closer-spaced in the top three gears. Bottom is 2/3 of direct, like an FW or S5. The top three gears are minus 14.3%, direct, and plus 12.5%, according the Sturmey document on Sheldon's site:

http://208.77.210.187/sturmey-archer/fm.html

That makes 2:3 - 6:7 - 1:1 - 9:8

The AW was 3:4 - 1:1 - 4:3


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 Post subject:
PostPosted: Mon Jan 10, 2011 8:33 pm 
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It needed 2 trains of epicyclics to get the closer ratios. If you pull it apart the planets are larger and have more teeth one end. So to reassemble you must be aware of the timimg marks on the planets, and line them up.
Theoretically there were 5 gear ratios in there.

I liked the theory of increasing 25% then decreasing 25% to get an indirect gear of -6.25%.
I last repaired SA gears nearly 55 years ago. Plenty of info out there.


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 Post subject:
PostPosted: Mon Jan 10, 2011 8:43 pm 
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keithglos wrote:
It needed 2 trains of epicyclics to get the closer ratios. If you pull it apart the planets are larger and have more teeth one end. So to reassemble you must be aware of the timimg marks on the planets, and line them up.
Theoretically there were 5 gear ratios in there.

I liked the theory of increasing 25% then decreasing 25% to get an indirect gear of -6.25%.
I last repaired SA gears nearly 55 years ago. Plenty of info out there.


blimmin heck!!

Thats a detailed answer, right there :wink:

It will take a good few trains full of epileptics to decypher it!!


( no offence meant with the above comment....its merely a play on words)


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 Post subject:
PostPosted: Mon Jan 10, 2011 9:06 pm 
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Take more than that to offend, I'm more likely to upset people by rightly describing their bikes as massed produced low end gas pipe tubed.....

SA were OK for gentle riders, but were too risky for the real stuff. I always preferred all gears in direct drive.

The ultra close also had 33.3% increase and 33.3 decrease for the lower gear, -11.4% from memory?

The other thing, if you want to take one apart, the end plate behind the cog, RH thread has a 2 start thread, and the position shoud be marked on the hub and end plate. They were so accurately made that if you picked up the wrong start then the wheel would be miles out of true.


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 Post subject:
PostPosted: Mon Jan 10, 2011 9:22 pm 
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thats some memory too!!

Sometimes I can't remember if I did a number 2 in the morning or not :lol:


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 Post subject:
PostPosted: Tue Jan 11, 2011 11:21 am 
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this is too much for my brain... Im gonna have to print this off lol....


It needs a rebuild so im gonna have to be doing it.. Got a fairly nice unknown 531 frame im gonna put it in, Just for some greenlaning realy...

From the looks of it the shell is in ok condition. It just seems the wheel was left out for some time in its early years so has suffered rust damage. Im guessing early years as some of the chrome is still there so its probably been saved and shoved in an attic or something...


Ive read it several times now that the alloy shell ones (like mine) have a tendancy to pop thru the shell, If this (hopefully not) was to happen while riding it. Is an AW shell the same? I.E could i use the guts of the 4 speed in an aw?

And cheers for the help guys.. Wealth of knowledge here :D


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 Post subject:
PostPosted: Tue Jan 11, 2011 11:54 am 
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Unlikely to break out, this is mostly in the US where they fit 22 tooth cog and use a small chainring. SA gears were never considered strong enough for enthusiastic use. Wish I could remember if the shells are the same, some alloy shells the LH end plate was virtually impossible to remove. Keep the alloy, the flanges are thicker, so less likely to break spokes.


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 Post subject:
PostPosted: Tue Jan 11, 2011 12:16 pm 
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Wicked :) Thanks very much for your help mate , Your an absolute legend. 8)


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 Post subject:
PostPosted: Tue Jan 11, 2011 1:19 pm 
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keithglos wrote:
SA gears were never considered strong enough for enthusiastic use.

I wasn't riding at the time, but I imagine the various records that were set with Sturmey gears must've required a fair degree of exertion:

http://www.sturmey-archerheritage.com/i ... ic-439.jpg

http://www.sturmey-archerheritage.com/i ... ic-539.jpg

There's a difference between a single record-breaking ride and a lifetime (or even a season) of grind, of course, but there are enough of these old hubs still going strong to make that assessment look a little uncharitable. I've put plenty of miles on Sturmey products over the years. If I'm not as strong as I was, I'm still just as enthusiastic.

Quote:
Wish I could remember if the shells are the same, some alloy shells the LH end plate was virtually impossible to remove. Keep the alloy, the flanges are thicker, so less likely to break spokes.

I'm fairly certain the shells are interchangeable - assuming an older AW with a threaded ball-cup, of course.

On the other hand, I generally prefer the steel shells to the older alloy models. If the alloy flanges are thicker there's very little in it, and I'd sooner break a spoke than crack a flange.

While we're here, I'll post links to Tony Hadland's excellent site. He's long been the best place to go for detailed SA information on the web. He's got pdf files of nearly every model, plus extracts from the post-war master catalogue, gear charts and dimensioned drawings of many components:

http://www.users.globalnet.co.uk/~hadland/gear.html

http://www.users.globalnet.co.uk/~hadland/sa/safm.pdf

http://www.users.globalnet.co.uk/~hadland/gill.html

There's also a wealth of information in the Sturmey Heritage site, but you have to dig for it:

http://www.sturmey-archerheritage.com/i ... tail&id=58


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