Bike Modification

A boring post about modifying the bike chain tensioner.

The Alfine 11 internally geared hub in the rear wheel came with a spring loaded chain tensioner.

You can see in the above photo the chain runs through two small cogs which form part of the tensioner.    Looking at the tensioner from a different angle allows me to explain the steel bushes in the cogs [A] have worn out.  The cogs now wobble around on the shaft of their securing screw.  As a consequence the chain doesn’t move smoothly and is noisy.  Moreover part of the tensioner is bent [B] and very close to the chain.  This probably occurred on one of the occasions when I either dropped or fell off the bike.

Buying a new tensioner is expensive.  Particularly as the only parts requiring replacement are two small steel bushes which are probably worth less than $0.01.  After searching the internet I found a supplier in Taiwan who claimed to be able to supply replacement cogs and bushes at an acceptable price.  However delivery may take some time.

I went onto Aliexpress looking to see if there was an intermediate solution.  Whilst doing that I decided to also buy a replacement pair of bike chain pliers.   My original pair are very small and my old hands are having problems squeezing them to break the chain link.  The new pair arrived today. Being larger are much easier to use.  I also ordered a generic single cog chain tensioner,

The first step was to test if the teeth on the generic cog aligned with the chain

They align

However when I fitted the tensioner to the bike the cog had insufficient reach to the chain.  Had I bought a lemon?

After thinking about it I modified the tensioner assemble.  This wasn’t a simple task as the tension spring inside the assemble initially worked in the wrong direction.  However once that problem was overcome the cog was able to be aligned with the chain.

 

I need to take the bike for a local test ride to ensure the tensioner is secure and works.  If it does I will probably cut off the surplus piece of the cog shaft with the angle grinder.  It sticks out and will likely bend or break the tensioner if the bike falls over.