BB & Chain Line

[Surly LHT]

(03-16-2010, 08:43 AM)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