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Old 09-26-06, 10:03 PM   #1
brianappleby
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can you tell if a cassette is worn by looking at it?

If a cassette is in need of replacement, will I be able to tell by looking at it, and comparing it to a brand new one?
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Old 09-26-06, 10:14 PM   #2
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To a point. Literally. When new, the tops of the teeth on the cogs have a flat area at their apex. As they wear, the flat area starts to disappear and are replaced by points. Also common is for the cogs to take the shape of a sharks dorsal fin. Of course, the chain skipping on the cogs is also a great way to tell that its worn....
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Old 09-26-06, 10:19 PM   #3
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the dorsal fin thing makes sense, but to clarify your first point:

If i'm looking at the cog along the chainline, the top of the teeth should be squared off on a new cassette, but "pointy" on a worn one?
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Old 09-26-06, 11:12 PM   #4
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Quote:
Originally Posted by brianappleby
the dorsal fin thing makes sense, but to clarify your first point:

If i'm looking at the cog along the chainline, the top of the teeth should be squared off on a new cassette, but "pointy" on a worn one?
If the cog teeth get to the 'pointy' stage, its long gone, and only the stretched chain that went with it would allow the cassette to continue being ridden/used.
Usually/more often a new chain will skip on those cogs worn beyond a useable limit. Those being the cogs most ridden. Its rare to have more than 2 cogs be at this service limit, since most riders will usually spend 80% of their time in only 2 or 3 cogs.
Best way to tell is when a new chain does go on, shifting is well adjusted, and the new chain does skip consistently skips on some cogs. You can try to get replacement cogs for those worn, or get a full cassette.
As for visible 'hooking' of the cog, if one gets to that point, its been long gone.
Best way to insure best longevity for a cassette/cogs is to check the chain often and replace it when it approaches service limit. That will assure a significantly stretched chain isn't prematurely wearing the cog teeth.
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Old 09-27-06, 12:45 AM   #5
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Generally, you'll notice your chain skipping under hard pedaling long before the cogs are worn down to an obviously-visually-worn state.
Here's an example of teeth worn to a shark-fin point, as viewed from the side on a granny chainring from my brother's road-triple crank.

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Old 09-27-06, 08:21 AM   #6
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[QUOTE=timcupery]
Here's an example of teeth worn to a shark-fin point, as viewed from the side on a granny chainring from my brother's road-triple crank.

QUOTE]

That one looks more than just worn, it looks like it's hit something hard, the leading edge of the teeth are bent. Is there more to the story?

Al
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Old 09-27-06, 10:06 AM   #7
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Originally Posted by timcupery
Here's an example of teeth worn to a shark-fin point, as viewed from the side on a granny chainring from my brother's road-triple crank.

QUOTE]

That one looks more than just worn, it looks like it's hit something hard, the leading edge of the teeth are bent. Is there more to the story?

Al
You can't hit it with something to produce that regular pattern on all the teeth and not damage anything else.
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Old 09-27-06, 01:09 PM   #8
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The picture link has disappeared for mine... but anotherpoint to consider.

In my opinion, it is difficult to tell visually if a cogset has worn enough to be replaced. This has to do with the increased radius of the curved section between each tooth. This may vary between each cog, depending on how often a rider remains in particular gear over the life of the cogset. Indeed, there might be an argument that because smaller cogs (13-12-11T) rotate faster for any given pedalling cadence than their larger brethren, they are more likely to wear faster than the others.

The only way, IIRC, that you can physically measure the wear on cogs and chainrings while they are installed on the bike, I think, is with a tool, the Rohloff HG-Check Sprocket Wear Indicator. It looks like a chainwhip, but comprises a new chain with a piece of bar shaped to correspond with the half-inch pitch between the teeth. The chain is laced around each cog, and the bar is used to tension it. The last free link is then moved in and out of its corresponding tooth. If the link moves OK, the cog is fine; if the roller interferes with the tooth and any resistance if felt, it is not. Conceivably, it is a very simple tool to make up.

Otherwise, you have to put on the cogs/chainrings, pedal hard and see if the chain slips.

Remember, that the teeth on many cogsets have been deliberately designed to appear "bent" or "chipped" or "worn" lower than the others to assist in the shifting process.

Edited.

Last edited by Rowan; 09-27-06 at 01:19 PM.
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Old 09-27-06, 01:45 PM   #9
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Quote:
Originally Posted by Rowan
Otherwise, you have to put on the cogs/chainrings, pedal hard and see if the chain slips.
And that's the main practical thing here. If it rides okay with a new chain, then it's okay.

Quote:
Originally Posted by Al1943
That one looks more than just worn, it looks like it's hit something hard, the leading edge of the teeth are bent. Is there more to the story?
No more to the story. It's just worn. Really worn. As operator noted, the regularity of the waering-down profile indicates that it's probably from the chain. And it is.
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Old 09-27-06, 02:37 PM   #10
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Another thought on the Rohloff tool... I have achieved the same effect using a chainwhip. Thread three full links (six rivets) around the cog, and lever the chain tight. Pull the free end of the chain and check to see if you have resistance. I recall it working some time back. I generally replace cogs and chains together, so it becomes a non-issue for me.
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