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I was having terrible problems with shifting with my Ultegra 9-speed. No matter what I did (and I tried every adjustment possible including checking the alignment of the rear derailleur hanger) my shifting was terrible and I had lots of issues with chain rub. Given that most components on my drive train are at least a few years old (my shifters and rear derailleur were in fact 9 years old) I thought it was high-time and a good excuse to upgrade, so I installed Ultegra 6700 and now everything works great.

At the same time I decided to change my cross bike from single speed to a geared bike, so I thought I might as well use my old components off my road bike since perfect shifting was not a concern for my beater cross-bike. However, when I installed the bottom bracket and crank arms from my old bike and spun the cranks I noticed that the chain rings were not traveling in a perfect plane. So I took them off and reinstalled... same outcome. Then I installed a spare set of Ultegra crank arms and had the same issue (although the issue did not seem quite as pronounced). Furthermore, after installing the second set of crank arms I noticed that my left and right crank arms were not perfectly lined up... just slightly off in alignment. I rechecked the installation of both crank arms and still the alignment was off.

The bottom bracket seems fine, but I wonder if this is a bottom bracket problem or if its a problem with my crank arms. The fact that both sets of crank arms show the same issue makes me suspect this is the bottom bracket. So is it the BB, the cranks arms, or is there something else I'm not thinking about?
 

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If it's a very very slight wobble, you should be fine. Anything more, it's most likely your BB which should be replaced. Based on your description, no way it's the crank arms or spider, but just maybe your chainring is slightly bent (which can usually be fixed/bent back if you've got a good touch).
 
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