Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

1/8" chain and Sturmey Archer chain tensioner

Notices
Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

1/8" chain and Sturmey Archer chain tensioner

Old 05-10-21, 09:25 AM
  #1  
robo
Senior Member
Thread Starter
 
robo's Avatar
 
Join Date: Apr 2005
Location: Minneapolis, MN, USA
Posts: 1,143

Bikes: 1990 Burley Bossa Nova, 1992 Paramount PDG-70, 1993 Specialized Stumpjumper, 2005 Jamis Dakar XC Pro, 2007 Rivendell Bleriot

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 27 Post(s)
Likes: 0
Liked 4 Times in 2 Posts
1/8" chain and Sturmey Archer chain tensioner

Replacing a worn chain on my electric cargo bike, and I went with a 1/8" KMC e101 (https://www.kmcchain.com/en/product/...1-single-speed) since it seemed like the best chain for the job and it's a tough job being an electric cargo bike that often is nearly 300lbs fully loaded.
The problem is, the bike uses a Sturmey Archer chain tensioner (https://www.sturmey-archer.com/en/products/detail/cts86), and turns out this chain tensioner is only designed for 3/32" chains. The 1/8" chain can move through it, but makes a clacking noise as the links hit the sides.

Is there a way to increase the spacing of this tensioner, or should I just replace it or run a narrower chain?

Last edited by robo; 05-10-21 at 09:59 AM.
robo is offline  
Old 05-11-21, 07:20 AM
  #2  
JohnDThompson 
Old fart
 
JohnDThompson's Avatar
 
Join Date: Nov 2004
Location: Appleton WI
Posts: 22,546

Bikes: Several, mostly not name brands.

Mentioned: 133 Post(s)
Tagged: 0 Thread(s)
Quoted: 2575 Post(s)
Liked 1,214 Times in 766 Posts
Presumably, the original 3/32" wide chain worked well enough for you to wear it out. You might be able to cobble something up to make the SA tensioner wider (spacers between the pulleys and the cage, perhaps?), but I suspect that a decent 5-6-7 speed 3/32" chain would work fine without any modifications.
JohnDThompson is offline  
Likes For JohnDThompson:
Old 05-12-21, 09:22 PM
  #3  
adipe
Senior Member
 
Join Date: Aug 2015
Posts: 156
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 50 Post(s)
Liked 11 Times in 10 Posts
just go with a magic gear setup IF you don't have a mid-drive motor setup (i suspect you have a singlespeed setup and therefore a motor hub).
https://eehouse.org/fixin/formfmu
in order to use this you need to have the chainstay length in mm. very rarely is it a non integer value for a vertical dropouts frame so it's not very hard to get it in case you don't find the geometry numbers on the webs.

it's hard to explain how you can accurately measure the chainstay length using either a new chain or even a used chain (supposing you have a caliper at hand). it involves measuring a low enough chain slack - so you don't have too much error. then apply the a^2=b^2+c^2 thing. and if you have a chain (or different chains) that is not new then you can use a caliper. mount the chain so that you have a bit of tension in it, just hang some light load on one pedal. get the smallest possible distance measured and then the largest one (meaning some pairs of links more). then you get the actual length of the chain, after you do all this, having counted the pairs of links of that chain.

i have less than 0.1% chain wear after 5000 miles of pedaling with a singlespeed bike because i use a proper lube.
hebie chain glider

one more thing... if the electric motor is in the hub then you don't really need a 1/8" chain. chainline alignment is almost always impossible to get accurate enough for a 1/8" chain. the only advantage 1/8" chain has is being able to work with higher loads (useful IF having mid-drive motor with a geared hub) but then again... the frame should be rigid enough and the chainline should not be off by more than 0.1mm, otherwise you would have a discomforting noise and vibration. 1/8" chain is harder to clean/lube too.
adipe is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.