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chain stretch

Old 08-13-14, 12:27 AM
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trek330
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chain stretch

I bought the Park Tool to check for chain stretch and lo and behold all my chains are too long.My tool has a .5 and .7 readings and the .7 side easily enters the chain.Does that mean replaceing the freewheel with the chain is mandatory?Strangely enough the chains don't slip and shift fine.
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Old 08-13-14, 12:31 AM
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You need to check the teeth on the chairing and the freewheel. If they look curved and more like a sharks tooth, then you need to replace the chain and the gears. If you don't, a brand new chain will wear out quickly and then it may break and you'll be stranded. If the gears look wore out, change them with the chain.
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Old 08-13-14, 01:13 AM
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A chain and sprocket will work fine together until about 2% stretch, but if the chain is stretched much beyond 1/2% stretch, a replacement chain is likely to skip on the used sprockets.

Given that you've passed the "safe" replacement mark, odds are you'll need a new cassette if you replace the chain.

You have 2 choices here.

1- do it the old fashioned way, and keep riding until the chain begins to slip.
2- buy a new chain and cassette, but install only the chain and cross your fingers. If it runs on the old cassette, save the new one for next time. If it skips, replace the cassette.
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Old 08-13-14, 05:47 AM
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No need to add to FB's advice to the OP, but I will add a couple precautionary notes to others dealing with possible drive train wear:

You don't need a tool to check for wear. It's a waste of money for a consumer, with the possible exception of someone who has a stable of bikes. All it takes is a ruler, which is far more accurate - one can find multiple examples on the forum where someone's gauge said the chain was worn more than it was. The fact that a tools exists does not mean it is useful for everyone. Google measure bike chain wear.

Don't depend on your eyes to detect cassette wear - it happens before even the sharpest eyes can detect it. The test is how a new chain behaves, or how the cassette works when switched to a different bike that has an unstretched chain.

Chainrings can become less efficient long before they get to the shark's fin stage, but of course it's a matter of utility vs. budget as to when you replace them.
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Old 08-13-14, 08:47 AM
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Not only is a chain measuring tool a waste of money, it doesn't properly measure chain elongation. If you're interested, here's a good writeup on it: http://pardo.net/bike/pic/fail-004/000.html

I use and recommend an 18" steel machinist's rule. These are thin stainless steel with fine scribed markings which makes accurate measurement easier. The pix below show a chain exhibiting 1/16" elongation over 12" (13"-1"= 12"). I start from the 1" mark because the scribes on both sides of 1" help center it on the pin.



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