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Old 03-31-06, 05:00 PM   #1
spacecadet
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8-speed chain line and rubbing

Ok, I just upgraded my old bike. I had the frame rear triangle widened (to 130mm). I put on an a new wheel with an 8-speed cassette hub. I also replace my inner chain-ring (shimano ultegra) from a worn 42 to a new 39 (I kept the big 53 ring). I replaced my old ultegra rear with a new 105 rear derailler. Seems to work fine with a minor nuisance: Using the small chainring with a rear cog gear between the bottom and 3 cogs from the bottom, the chain rubs on the large chainring on the bottom of the chainring. I brought the rear wheel back as much as possible to avoid to reduce the angle. I'm wondering if the problem would be reduced with a 42 inner chainring? Trying to see if the large chainring is warped, but hard to tell. Is this just unavoidable with the new wider cassettes, creating larger angles on tighter frames?
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Old 04-01-06, 06:22 AM   #2
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The chain rubbing on the BIG ring as it leaves the smaller ring is anoying. I have not seen it (or heard ) as bad on my 8 speed bikes, as usually I get it only when I cross chain from the smallest cog on the rear to the small chain ring , 39 or 42 it does not matter. Now that your chain stays have now been spread to 130mm is the alignment of the stays equal on both sides of the BB? Are you using the matching BB that is suggested for the crankset ( 105 8 speed?) Are you sure that the chain is not rubbing on the FD cage? as 'trimming' of the FD could be all you need to do when you hear the noise.
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Old 04-01-06, 12:07 PM   #3
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Check your chain line. Put the chain on the big chainwheel, smallest cog. From the back of the bike, look stright down the chain. Close one eye and slowly move your head back and forth until the small chainring is as thin as you can get it, now look at which cog it is lined up with, it should be no. 4 starting from the largest cog. If its lined up with 2 or 3, you need to move your chain line out.
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Old 04-01-06, 07:37 PM   #4
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San Rensho and ccdisce:
Good suggestions. I tried eyeing the alignment. It looks OK according to your check. The new 130 mm spacing is just enough the cause the chain line rubbing on the lowest 2-3 cogs. I didn't even think about the bottom bracket spacing. I'll check that.
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Old 04-01-06, 07:37 PM   #5
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San Rensho and ccdisce:
Good suggestions. I tried eyeing the alignment. It looks OK according to your check. The new 130 mm spacing is just enough the cause the chain line rubbing on the lowest 2-3 cogs. I didn't even think about the bottom bracket spacing. I'll check that.
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Old 04-07-06, 12:44 PM   #6
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I just got a Salsa 42 inner chainring. There is less chain rub than with the 39. With the 39, the chain would rub the large chainring with the 1,2, and 3 smallest cogs. Now, with the 42, it only rubs with the 1 and 2 smallest cogs. I also got some chainring spacers (.6mm) which I haven't used yet. They are female spacers. Now the question is: Should I move the inner ring in, or the outer ring out? It is possible to do either.
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Old 04-07-06, 01:19 PM   #7
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I used the spacers so that the outer ring is pushed out (.6mm). It works fine. Not too much space that the chain can get stuck between rings. Just enough that there isn't chain rub except on the smallest cog. Shifts fine into the big ring. Life is good.
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Old 04-07-06, 03:34 PM   #8
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You don't need to space between the rings. Add a bottom bracket spacer between the bottom bracket and the frame. These are available in 1, 1.5, and 2mm thicknesses. If it is rubbing the big ring with the chain on the 39 and the three smallest cogs then try a 2mm bottom bracket spacer. This will move the entire crankset out.

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Old 04-09-06, 06:46 PM   #9
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I thought of putting a spacer on the bottom bracket, but the chainring spacer seems to work fine. Wouldn't using a bottom bracket spacer create chain angle problems when using the large ring with the larger rear cogs? I also checked the chain line and it measured 43mm (both front and rear), so alignment seems to be OK.
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