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Chain needs replacing?

Old 05-14-11, 03:29 PM
  #1  
Buggington
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Chain needs replacing?

Hi

I've been having a problem with the chain on my mountain bike skipping as I go over a bump fairly fast (it wouldnt be slow, would it? ). The LBS says that my chain is quite badly stretched and that when it gets replaced all the sprockets and chainrings will need to be replaced so that they will all mesh correctly and not skip again, all at a coat of about £80.

I have two questions:
1. Does the chain sound like it needs replacing, or have I just got minor tuning to do? It's done 1100miles, none of which have been particularly kind.
2. Does the part about needing to replace all of the sprockets and chainrings sound Bout right? Apparently even though they all look unworn to the eye (which they do) they can still skip.

I just want to make sure that I'm not wasting my money, as £80 is quite hard to come by as a 16 year old kid!

Thanks,
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Old 05-14-11, 04:10 PM
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The most likely problem is that running a new chain on an old cluster often results in the chain jumping off the cogs. The effect is most pronounced on the smallest cogs. I'd find it unlikely that your chainrings need replacing after only 1100 miles. If the mechanic has satisfied you that the chain is indeed worn out, replace that and the rear cluster (or at least the smallest cog or two on the rear cluster). See how it works. Only if you're having trouble with shifting on the front chainrings would I consider replacing those.
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Old 05-14-11, 04:40 PM
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I can't say this often enough. One measurement is worth 1,000 opinions.

Start by measuring the chain wear (stretch) yourself. It's easy enough and once you learn how, you'll always know where you stand. You'll need a 12" ruler (I assume imperial rulers are still sold in the UK, but if not you can use 305mm as your base measure)

Since chains have 1/2" pitch every pin is half an inch apart. Wear allows the links to move apart a bit, and over a distance the error becomes big enough to measure easily. Stand the bike up, press on a pedal to tension the chain enough to pull out all the slack, and measure from 1/4" to 11/3/4" (I don't use the end of the ruler because it's often worn and hard to find the line). On new chains pins will line up the same at both ends. On stretched chains the far pin will be beyond the mark.

Up to 1/16" beyond the mark is fine
1/16" to 1/8" replace the chain, and the odds favor the cassette being OK, the odds worsen as you near the far end of the range.
1/8" or more the cassette is likely toast, and there's a decent chance the chainrings are also.

Once you've measured your chain, you'll be better equipped to decide how much you need to spend.

BTW- if your chain is stretched beyond 1/16" over 12" you need to give more thought to chain lube, both the choice of lube and the frequency and method of application. With decent care you should be able to do much better in the future.
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Old 05-14-11, 06:38 PM
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Even more important than lubing the chain is keeping it clean. Putting fresh lube on a dirty chain can be worse than no lube. Invest in a brush (even if it is a toothbrush, although your LBS should have more specific brushes you can buy) and some degreaser to keep the chain clean, or in the least wipe it down whenever it looks dirty.

Good chain lube is clear. If you touch your chain and get black gunk on your hands, you need to clean your chain because it is too dirty.
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Old 05-15-11, 10:16 AM
  #5  
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Originally Posted by igknighted View Post
Good chain lube is clear. If you touch your chain and get black gunk on your hands, you need to clean your chain because it is too dirty.
All it takes is one ride to have black lube on the chain, even after a thorough cleaning. The color is not an indicator of the need for cleaning. If it was, you'd need to clean the chain after every ride.
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Old 05-15-11, 11:14 AM
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https://www.sheldonbrown.com/brandt/chain-care.html
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Old 05-16-11, 02:59 PM
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Wow...this is a lot of info! Thanks everyone!

FBinNY - I had no idea there was so much science to all that - I'll steal a steel rule (ha ha) from the workshops at school and have a measure.

In my oh so humble opinion, DaveSSS is right with his comment about always cleaning it - especially as it's a mountain bike which spends a fair amount of time on dusty/muddy tracks. I do use a toothbrush on the chain, but I have a sinking feeling that I'm just pushing dirt into the links anyway.

Sheldon Brown's website is a mountain of information - I should refer to it more often, and what he says about the sprockets and skipping is what the LBS described to me - so I shall have a measure, according to FBinNY's suggestions.

As the subject of the lubrication has come up quite a few times here, what do people suggest I use, and how often, considering it's a very well used mountain bike?

Thanks,
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