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BB & Chain Line
#1
I installed a new BB - just 2mm longer than the old one. Now it seems as if the chain line is off (9-speed mtn). I know with cassettes and derailers its not possible to have a straight chain line for all gears but would just 2mm be enough to throw off for the high and low gears where it skips? It's not even climbing to the highest gear.

PS I justed started working on my own bike and this site has been great to learn how to do it myself.
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#2
Here is something that may help ya.
http://www.sheldonbrown.com/bbsize.html#chainline
Good maintenance to your Bike, can make it like the wheels are, true and smooth!
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#3
(03-16-2010, 12:43 PM)chris Wrote:  I installed a new BB - just 2mm longer than the old one. Now it seems as if the chain line is off (9-speed mtn). I know with cassettes and derailers its not possible to have a straight chain line for all gears but would just 2mm be enough to throw off for the high and low gears where it skips? It's not even climbing to the highest gear.

PS I justed started working on my own bike and this site has been great to learn how to do it myself.

How are you checking your chain line? 2mm is a lot but you don't have to have to have it right on the money for it to work good.To check your chain line you need to have the rear chain on sprocket 5 going down from the top of the back sprocket and the front chain ring you need that one in the middle sprocket to see if its right in line 2mm is a lot.1mm will work ok for the most part mine is off a little but it works great mine is off 1mm so I know this little bit off still lets it work good. I am guessing that that your 9 speed you also have three chain rings on front if I am right then check your chain line like I told you to do. sheldon brown has more info on this but he has lot of pics to show you better but I learn it from there too. Why did you go with a longer BB? There are a lot of videos here to help you out with your bicycle, Alex has worked his heart out for all of us. So we can do our own work on our bicycles. Thanks Alex
My dad always told me a Sledge a matic can fix any thing.
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#4
I haven't measured the chain-line it just looks off. Longer BB is due to availability - closest new size was 2mm longer or 1mm shorter, I chose the longer. I may try the shorter BB which I also have and see how that does. Thanks for Sheldon Brown tip. I'll also check the chain-line in the middle chainring and rear gear. It may all have to do with my new rear derailer and cable set-up in which case I have more videos to watch. Thanks for the help.
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#5
It was the new derailer that was causing the problems - I had installed a 1:1 rairo with 2:1 ratio shifter. Who knew? Now I do. Chain-line looks good in the centers. Thanks for the help.
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#6
Glad it turned out good for ya Smile
Good maintenance to your Bike, can make it like the wheels are, true and smooth!
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