Bicycle Mechanics - Chain line question
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10-16-03, 04:26 AM
Yesterday I installed my 105 double crank on my bike after I received my new 5500 bottom bracket. I tightened the bottom bracket and cranks down fully and adjusted my derailleurs. The bike shifts great, except while in the largest chainring and smallest cog (13T) the chain slightly touches the next rear (14T)cog. The chain I have is a HG50 9 spd so that is not the problem. Just from eyeballing I can see my chain line is off. The crank chainrings are closer in to the largest cog and off center. What is the proper way or a safe way of fixing this??? Do I buy a 5500 68X118 for triples??? Slightly adjust the bottom bracket outward??? Or not tighten my crank arm all the way in??? Before I had this 105 setup I had an old Sugino crank that I just adjusted the bottom bracket outward and it worked fine. I'm just not sure if this is healthy for the bike. Thanks in advance for any help. :)
The crank arm must be tightened so don't use it to move the chainline. Moving the BB cartridge side to side is ok and standard practice. A little bit of movement can be had just by screwing one side in as the other side is screwed out. If an unacceptable gap develops spacer washers 2 and 3.5mm wide are available. 3.5mm is about as much as you can safely move the BB side to side though and there is no guarantee that this much is available on your bike. Limits are imposed by the length of the BB shell versus length of the BB bearing housing. Some L side cranks start getting really close to the BB shell. If this is not enough, then you may have to go to a longer axle. Steve
10-16-03, 05:24 PM
Do not back out your botton bracket without shimming it. Remove the bottom bracket, install the appropriate shim(s) then tighten it back down.
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