Technical > Transmission

How do my teeth look?

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Matt2matt2002:
Many thanks folks. All good information and given graciously.

Andre:
Yes, 4500+ miles.
I thought I'd flip the ring and cog at next chain change.
( If I'm still here! )

Mickeg:
Good words on identifying the wear by looking at the tooth and adjacent hole. I can see some slight wear.
My set up is 38*17.
Fitting your worn 0.75 chains onto the Rohloff?
I take mine off for replacement at that point.
What is your reasoning?

Steve216c:
Looking forward to seeing your pictures.

PH:
Thanks for your comments.
So, you don't measure your chains routinely?
Looking out for a 0.5 or 0.75 change/wear point?
At what point would you change the chain?

Once again many thanks for opinions and my further questions are asked with respect.

The attached pictures were taken at the same time as fitting the new chain.
The EBB turned fine and the 2 screws gripped fine.
I noted that it could slide across but I'm sure I maintained the original ' line'.
And the position / rotation of the EBB looks ok?

mickeg:

--- Quote from: Matt2matt2002 on July 12, 2021, 02:24:12 PM ---...
Mickeg:
Good words on identifying the wear by looking at the tooth and adjacent hole. I can see some slight wear.
My set up is 38*17.
Fitting your worn 0.75 chains onto the Rohloff?
I take mine off for replacement at that point.
What is your reasoning?
...

--- End quote ---

This article is the basis for my thinking:
https://www.sheldonbrown.com/chain-life.html

I cut notches in one tooth on my sprocket and one tooth on the chainring so that I can always put the chain back on the same way.  The notched tooth always gets a link that has outer plates over that tooth.

The chain elongation occurs at every other link, the links with outer plates.  And if you have an even number of teeth on your sprocket and chainring, every other tooth will wear to match your chain elongation.  I could see that every other tooth on my sprocket wore differently according to that theory.

So, I have no real reason to not put worn chains on the bike if I will keep the amount of wear on those chains to a rough equivalence.  For example, if I put a chain on with 0.75 percent wear and then take it off at 1.0 percent and put another one at 0.75 percent elongation on.

Yes I could keep putting new chains on it, but I would rather get some more use out of my old ones.

This won't work for you because you use a sprocket with an odd number of teeth.

I have no clue why Thorn has used a 17T sprocket as their standard, but I suspect that they are trying to keep the amount of wear on each tooth the same as adjacent teeth.  If I was running a bike shop, I would be inclined to do that too.  I doubt if explaining to a potential customer how sprocket teeth wear is a useful sales tactic.  But I worked in a bike shop years ago, I built up my Nomad Mk II from parts, and am an engineer by training.  I cut notches into the teeth on my bike when it was new based on that article, as I could see the logic in it.

mickeg:

--- Quote from: Matt2matt2002 on July 12, 2021, 02:24:12 PM ---...
The attached pictures were taken at the same time as fitting the new chain.
The EBB turned fine and the 2 screws gripped fine.
I noted that it could slide across but I'm sure I maintained the original ' line'.
And the position / rotation of the EBB looks ok?

--- End quote ---

The middle photo shows that the screws that lock the eccentric in place will be pressing in on a thin part of the eccentric.  Your eccentric is different than mine, so perhaps it is stronger and you can do that.  But I recall reading when I first built up my Nomad Mk II that the screws that lock the eccentric in place should press against a thick part of the eccentric so that the eccentric is not bent or deformed, other than the tiny little depressions that the screws will press into it.

Note the first attached photo, I have the thick part of my eccentric on the bottom where the screws are.

Second photo, just in case one of those screws gets loose, with a rubber band wrapped around both screws, they are unable to rotate and can't fall out and get lost.

PH:

--- Quote from: Matt2matt2002 on July 12, 2021, 02:24:12 PM ---PH:
Thanks for your comments.
So, you don't measure your chains routinely?
Looking out for a 0.5 or 0.75 change/wear point?
At what point would you change the chain?

--- End quote ---
No, never measure, not with a single chain line anyway, I don't see the advantage.  Worn chains works fine with equally worn sprockets and chainrings, the reason they don't work with a cassette is that the sprockets don't wear at an equal rate, so it'll start skipping on those less worn. plus the constant sideways flexing weakens the plates. 
I've never taken a chain to the limit, when the sprocket looks like it hasn't got much life left it gets flipped along with the chainring and a new chain added. That's usually around  15,000 miles and I'm quite conservative, I might see if the current ones last till 20,000. 
Neither do I waste much time cleaning chains, they get a wipe, oiled and the excess wiped of.
Each to their own of course and whatever makes you happy, with enough time and effort you could probably make a sprocket and chainring last a lifetime, but for me life's too short for that sort of bother.

PH:
Not mine, but this photo often does the rounds in such discussions, this is what a worn sprocket can look like  ;)
http://www.swedentoafrica.com/wp-content/uploads/IMG_0219_960x640.jpg

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