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Discussion Starter · #1 ·
or not installed right.
So I'm building my wife's bike and I got the BB and the cranks installed. The cranks spin nice and smooth but as I'm spinning the them I notice the chain rings are wobbling about 1/4" left to right. Everything is nice and tight, BB, chain rings and crank arms, but the "dynamic chainline" issue has me a little worried. Any ideas anyone??
 

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bent

Oh yes, something's not right there. Have you taken off the crankset to see if the bottom bracket spins true? Assuming it does, did you by any chance disassemble the chainrings and forget to put a washer on or something? If it's a 1/4 inch out, this should be pretty easy to notice exactly what is bent just by eyeballing it. Most cranks are cast and being that much out is not good because cast "anything" does not like being bent back into shape. What type of BB? Square taper, Octalink, Isis? I know some BB's only go on one specific way, I think it's one version of Octalink that has an index spline?
 

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Discussion Starter · #3 ·
The BB is a DureAce cartridge type. Didn't take the chain rings off the crank at all but I'll check to see if all the washers are in there. I'm going to double check the BB to see if it's in the right way. That reminds me, the left and right side on the BB? That's if you're sitting on the bike, right? So the left side would be the non-drive side, Yeah?

Thanks for your reply.
 

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Figure it out

robbyracer said:
or not installed right. So I'm building my wife's bike and I got the BB and the cranks installed. The cranks spin nice and smooth but as I'm spinning the them I notice the chain rings are wobbling about 1/4" left to right. Everything is nice and tight, BB, chain rings and crank arms, but the "dynamic chainline" issue has me a little worried. Any ideas anyone??
Is it the crank or the chainrings? Hold something (like a partially straightened paper clip) on the seat tube so that it just touches the chainring bolts as you spin the crank. It will be obvious if the crank is wobbling. If not, then it is a bent chainring.

Assuming that your BB is OK (i.e. not loose - it's extremely unlikely that it's bent), you have to straighten your spiders and/or chain rings. If it's a CF crank, then only your chain rings can be straightened. If the crank spiders are bent, you can even them out as follows:

Place the bike on its side with the crank supported on a block of wood at the axle. With another block of wood or a stout dowel placed at the end of the offending spider(s) give it a whack with a hammer. Check for change in alignment. If you got no change, hit it harder next time. Repeat until all the spiders are even. You may need to bend them away from the frame (brace the right crank on the block of wood) or toward the frame (brace the left crank).

Once the spiders are even, check the chain rings with the same technique except put the point of your screwdriver at the teeth of the rings (most likely the big ring only if the spiders are even). Straighten the chain ring by placing a large adjustable wrench over the ring with the jaws adjusted for a slip fit over the ring. Bend gently, and check alignment. Repeat until you've got it right.

Even with the chain rings dead straight, you still will get some deflection due to pedaling forces, but that should greatly improve your situation.
 

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You probably misaligned the splines when you attached the cranks. It's not hard to do. It's easier to get alignment/engagement right by completely removing all the fixing bolt hardware from the crank before mating the crank to the BB.

(If this is the case, hope you didn't damage the crankarm splines from your past attempt).

Good luck.


robbyracer said:
The BB is a DureAce cartridge type. Didn't take the chain rings off the crank at all but I'll check to see if all the washers are in there. I'm going to double check the BB to see if it's in the right way. That reminds me, the left and right side on the BB? That's if you're sitting on the bike, right? So the left side would be the non-drive side, Yeah?

Thanks for your reply.
 

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Discussion Starter · #6 ·
ok so I pulled everything apart last night and reinstalled it all. No wobble and more. Hmmm, go figure.... I must have installed something wrong but it's all fine now. I kinda miss the old skool stuff.
Thanks for the input.
 
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