Surly 1/8 cog - doesn't fit chain!

Posted on Sun 20th, February 2011

• #1

yodasm9

Hi folks, i've seen this problem once before on a chrome token cog but figured it was a one off.

I have a surly 17t 1/8 cog which I want to run with a TA 48t 1/8 chainring with an izumi toughness chain.

So far so good, right?

However when I run the chain round the cog it catches and unseats from the teeth...

I have a cheap black token cog and the teeth are much narrower than the surly and the chain runs fine.

No issues with the TA chainring either.

Are steel cogs machined with thicker teeth than alloy ones?

Everything is 1/8 so I am stumped... any ideas?
• #2

deleted

is the cog new and the chain and chainring old?
• #3

yodasm9

cog and chain ring are only slightly used, the chain is brand new.
• #4

grumpy

How much is slightly used, if there is appreciable wear on the teeth of the cogs the chain will not seat into the teeth but sit on the tops as the wear rate will probably be greater than the half inch span of the new chain.
• #5

yodasm9

just tried a sram pc1 chain on the cog and it fit fine.

compared both chains and the spacing is larger on the sram chain - Im guessing NJS chains have narrower tolerances.

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