Bicycle Mechanics - Bottom Bracket spacing
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06-05-08, 08:02 PM
I was assembling a mountain bike today, (Schwinn Homegrown) and found that when I shifted into my small chainring up front the chain would rub the tire and the FD cage was almost touching the tire, which was only a 2.1 by the way.
I had a 5mm spacer laying around and put it between the drive side BB cartridge and the frame then tightened it all up. Just rolling around the back yard it seems OK. I know the proper way to fix this would be to buy a wider BB cartridge but this one is almost brand new. Its a 118 width. Does anybody think this will cause a problem.
06-05-08, 08:21 PM
5mm? Yeah that's a problem.
Does the left cup even contact the bb without being flush against the frame?
06-05-08, 08:29 PM
I don't think so, it went right up against the frame without alot of torque.
06-05-08, 08:34 PM
Sounds like you've got the wrong BB size for the crank you're using.
What is the crank exactly?
06-05-08, 08:40 PM
Octalink Hollowtech LX
06-05-08, 08:45 PM
118 should be a triple, not backwards is it?
06-05-08, 09:51 PM
Nope, its in the right way. I know my back wheel dish is just slightly off, maybe that is the problem.
06-06-08, 07:27 AM
My first guess was that your wheel wasn't in straight. If your alignment issues are only with the tire, then dish is your problem. Check your chainline to make sure that the middle ring of your crank lines up roughly with the middle of your cassette. If not, the spacer has to go and you need to dish.
06-06-08, 07:36 AM
If the non-drive side cup has a flange that stops it's progress before it snugs up against the main bb cartridge, you will have a real problem if you ride the bike.
A couple of things:
What is the width of your bb shell and what width is the bb itself made for? Many MTB's have 73 mm bb shells and the bottom bracket must be that width. A 68 mm bb won't fit properly. However, a NDS cup without a flange may be threaded in far enough to make it work or may compensate for a ds spacer. But, 5 mm is a lot.
If the wheel dish is off, that's the first thing I'd correct. That may solve the rubbing problem immediately.
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