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Old 10-28-19, 08:20 PM
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DOS
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Originally Posted by delbiker1
My house and bike stuff are a shambles right now, getting new carpet, so I cannot easily get pictures. My problem: I replaced an Ultegra 6500, 175mm crankset on a 2003 Lemond Poprad, with a used 170mm Dura Ace 7701/03, both doubles. After mounting the 7700 crankset set, adjusting the shifting and taking it for a ride, I was wiping it off when I got home and realized the inner chainring is extremely close to the chainstay. After a while of trying to figure out why, I measured the housing of the cranks that the spindle loads into and the Dura Ace is about 1/8 inch wider on each arm. I did not measure the distance between the chain ring and the crank arm before I removed it, but suffice to say it is not much. Question 1: How much clearance is needed between crank arm and chainstay? Question 2: To achieve that clearance do I need to change the BB to one with a longer spindle or are there spacers/shims available that would work? When I took it for a ride everything was working fine, but that small amount of clearance worries me.I looked at my other bikes and they all have considerably more clearance than on the Poprad, even with the 6500 installed. I am thinking that when the 6500 crankset was installed by the previous owner, the BB should have been replaced at that time.Originally it was a Sora crankset. Any info and suggestions on my questions are appreciated.
Spacers won’t make a too short spindle longer. The crankset determines spindle length so yes you need a BB with a spindle of the correct length for the crankset you put on the bike. In most cases some amount of mismatch is ok, it just means your chainline won’t be optimal. But if way off, you get problems like the one you have where you risk damaging the chainstay for lack of clearance between it at the crank. All that being said, I am surprised that the ultegra and dura ace cranks aren’t using the same spindle length. What BB is in there?
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