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Every Google search I've done over the past weeks has landed me on this great forum, so thought I would register. Basically my son gave me his 1996 Scott Apache adventure mountain bike in a box and I've rebuilt it with new bearing, cables etc.

The problem I have is the chain seems to be rubbing on the side cage of the derailleur, only when it's on the high front and rear cogs.enter image description here The chain is two links shorter that the original which was to badly rusted to re-use. Old chain = 110 New chain = 108 I did rap the new chain around both large cogs and added two which gave me the 108. Here's a couple of images:

enter image description here

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    In your second picture, are you in the Big/Big gear combination? Could be 108 links isn't enough and your derailleur is being pulled too tight ? Was it a new chain? 108 seems quite short - 114 is a more common number. – Criggie Jul 24 '16 at 9:36
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    The chain is worn out, as is the cassette. But the rubbing is largely due to "cross chaining", with perhaps a tad of RD maladjustment thrown in. – Daniel R Hicks Jul 24 '16 at 11:55
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    Chain looks rather short by the way the RD's cage is almost horizontal! – Carel Jul 24 '16 at 18:38
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    chain is considered too short when it no longer snakes between the jockey pulleys. That is, it makes a straight line with minimal contact between the chain and the pulleys. – user26705 Jul 28 '16 at 23:14
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    Hey @Martin, don't use a worn chain and a worn cassette! I did once, and the chain broke and I flew over the handlebars! Go to a good bike shop and get a new chain and cassette. – rclocher3 Oct 29 '16 at 17:37
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Drive trains with a front derailleur system are designed with to have overlapping gear ratios ranges for each front chain ring to allow you to spend most of your time riding with the chain not stretched to the extremes of your rear cassette. Riding in your largest gear on both your front and rear is call Cross Chaining. Cross Chaining puts unnecessary stress on your drive chain system by forcing your chain to work through extreme angles to propel your bike forward.

Additionally, you'll get a grinding noise when using the most extreme gear combinations as you are forcing your chain to go from front to extreme back.

Best best to avoid that sound is to practice shifting both your front and rear derailleur. Starting out, it may feel awkward but your bike and ears will thank you ;-).

It is worth spending some money at the mechanic to give it a good inspection to make sure everything is in safe working condition as well. Nothing is worse than having something break when you are riding.

  • It's not that hard to shift "correctly". Just choose a "range" with the front derailer, then "fine tune" your gear ratio with the rear. When your choice on the rear is nearing one extreme or the other, and the front is positioned in the opposite direction, change the front. – Daniel R Hicks Mar 1 '17 at 12:48
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First and foremost, there is no good reason to ride for extended periods on the "big/big" combination. This produces the worst possible "chain angle" and begs for rubbing and other problems.

Second, from the pictures the chain and rear cogs appear to be worn out and in need of replacement.

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Sometimes the chain can make contact to the derailleur and so make a noise. Sadly, there are certain gears one should travel. These include everything except the combination of a small cog back with big cog front, small cog front with big cog back. If the derailleur are poorly adjusted, this can be the cause of the chain having some friction with the derailleurs. There are two solutions. Either you do not ride in these gears or you have it properly adjusted.

  • You have it backwards -- small/small and large/large are the ones to avoid. – Daniel R Hicks Mar 1 '17 at 12:49

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