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Old 08-29-11, 12:14 PM   #1
4rcticFlowers
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Tall bike chainline problem

Hey all, new to this forum, so I don't know if others have had similar problems before.

I have a real beater tall bike, and am having trouble with the chainline. The top frame is a little out of line with the bottom frame, I guess, and it's causing the cranks on both the drive side and left side to wear out. The bottom bracket is a square taper, and the holes in the cranks are wearing into circles, and as a result, have a lot of side-to-side play. Tightening the nuts holding the cranks on helps a bit, but the cranks are FUBAR.

I'm running it single speed, but I use a deraileur to maintain chain tension, which also seems to improve the horizontal chainline mismatch situation. I've tried setting the chain on different cogs, but it tends to jump back to its most natural seating.

I think if I could shift the chainrings on the top frame further out, I could get the line from the chainrings to the cog cluster straight. I think in order to do this, I would have to extend the square taper on the drive side of the BB. Can anyone think of a workaround for this problem?
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Old 08-30-11, 04:08 PM   #2
terbennett
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I've never done this but the bottom bracket for a triple will stick out more. I would recommend looking into that if you have a single crank.
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Old 09-03-11, 10:29 AM   #3
No Whey
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Originally Posted by terbennett View Post
I've never done this but the bottom bracket for a triple will stick out more. I would recommend looking into that if you have a single crank.
Long BB for a triple and a spacer or two under the fixed cup should move it out.
Just make sure you don't run out of room on the non-drive side.
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Old 09-05-11, 12:10 PM   #4
4rcticFlowers
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I actually have a triple crankset on there already; possibly just adding a little chain and putting it on the outermost crank rather than the middle would alleviate the problem, but then I'd be running a higher gear ratio than I'd want, given how heavy the tall bike is. Gotta keep the gear ratio low to push it up the hills.

I'm thinking maybe I could get a cheapo bottom bracket, cut off part of the spindle, and weld it to the end of my spindle. I'm not sure if that will work or not, since that might cause the crankset to be too far out...
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