opinions on sharpening chainring teeth?
 

what's your opinion on sharpening or cleaning up old, rounded chainring teeth with a metal file?

do sharper, more narrow teeth add much to shifting and overall performance over wider, but more rounded teeth? the effort would not make the teeth any taller, which intuitively seems most important.

does a little sharpening go a long way, or are you better served leaving the teeth alone?

in the words of andy kaufman, thank you very much.

Are you experiencing any specific problem at the moment? I'd expect that you'd be more likely to make things worse rather than better unless there's a specific and clear problem you can identify (like getting a bent tooth straight again). When my chain rings have gotten worn they have been very sharp - i.e. 'shark's teeth.'

OTOH, slightly worn cogs can frequently be improved by removing the little hook that forms on the back side of each tooth and letting a new chain settle properly on the worn cog rather than hanging up on the hook and then skipping.

LOL, my Grandfather used a sharpened bicycle sprocket on a shaft to rough the seat of the Windsor chairs he made... Other than that I have no comment.

i just have a really worn big ring on a bike that i would usually just replace, but its weird 122 bcd is difficult to find on the cheap. i know a newer ring would help the upshift from small to big ring, but didn't know if making these rounded teeth 'sharper' (more defined) would help. taller, would definitely help, but i can't do that without a time machine.

interesting. i also haven't tried a new chain. it's a flip bike i completely overhauled, but i'm trying to keep all costs down.

I've been under the impression that sharp ring teeth is a sign you are coming to the end of service life. I know one thing, be careful with leaning against it during rest. I still have a "sharkbite" scar on my right calf. Nasty.

I have no idea what line of thought suggests sharper teeth would improve anything. Can somebody explain this to me? All common knowledge suggests this would make them worse.

Any more material removal and you're working against yourself, IMO.

And if worn and stretched, THAT probably caused the chain ring issue. A new chain could buy the next owner some time, but I wouldn't attempt any additional removal of cog material, sharpening or otherwise. :rolleyes:

On any chain-driven device, as the chain stretches, it begins to wear away the teeth on the sprockets. Essentially, this is caused by the stretched chain widening the space between the teeth. Typically, the teeth begin to "hook over" as the chain rides higher upon the teeth due to its inability to fall down into the lower area between the teeth which transmits the drive forces into a higher position on the teeth side-walls. - This is because as the chain stretches, the distance between the link pins on the chain has increased and this precise fit into the teeth is no longer there. (Typically the chain is of a higher strength material than the sprockets. Escially when you are speaking about the front chain-rings which are typically aluminum, making the softer material of the front rings wear more rapidly than the steel rear freewheel cogs)
When you place a new chain onto worn and elongated teeth, you often have a "skipping" of the chain, (especially under load on smaller diameter cogs as the chain is in a tighter arc as it passes around the cog and is in contact with a fewer number of teeth when under load). This is caused by the new chain as it protests being forced into teeth openings that are not a match for the dimensions of the new chain. This usually manifests itself on high-miles bicycles on the cogs that had been used the most. (On a 1972 Schwinn Sports Tourer I worked-on recently, a new chain had been installed and there was an under-load skipping of the fourth gear rear cog. I deduced that this was the cog the user had preferred for most of his riding and therefore had the most wear. As those teeth were worn just enough to cause this, there was no other option but to replace the freewheel.)

So, sharpening the teeth will not typically make any difference as the center to center distance is no longer within original design specifications, and removal of more material only shortens the life of the already worn components. Replacing the chain will also shorten the life of the worn sprockets as they will wear in reverse as they try to fit back into the correct chain-pin spacing, taking away even more material from the teeth. On high miles applications, the only true solution is to replace chain and all sprockets at the same time so as to return everything to original design specifications.

^ thanks, hoss, for the thoughtful and long response.

i'm surprised there's nothing you can do for a worn ring. you can't even attempt to make the rounded teeth more triangle-like, like a new ring, to bring new life to it.

i think you nailed it. i filed the backside of the teeth where those little hooks were keeping the chain from moving up to the top of the ring. i added a newer sram chain, and it shifts pretty darn well.

unfortunately for me, i just sold the bike today, making someone very happy.

thanks again.

What about filing a 1/8" chainring for use with 3/32" chain? Has anybody tried it?

Sometimes when there's pot shifting from small to big it's because of heavy grro ing on the inside of the big ring. If there're heavy grooves or wear on the inside you file or smooth out the surface, rotating the ring 1 bolt may help as well.

"sharpening" was certainly the wrong term to use. but i thought the problem might have been with the rounded teeth. it ended up being a problem with the inside of the teeth as you've described.

this was my first peugeot project and my first french crankset, and i learned a lot from it. i feel like i'm in a much better position to tackle the next one. thanks, guys.