Bicycle Mechanics - Question regarding Cranks
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I have a mountain bike I use for light touring that has a cheap SunTour crankset with riveted on chainrings. I wanted to be able to take my chainrings off so I went and bought a FSA AlphaDrive crankset, mostly becasue it was only $70 Can and it fit my square tapered bottom bracket. But the FSA cranks don't tighten down as much as the SunTour ones did, so my fr. derailer is all out of wack due to the chainrings being father from the bottom bracket then they are supposed to be, also my chainline is off a little, not that it was perfect before, but it's worse now. I really like the cranks but I don't know if all this will cause problems, will the cranks loosen up after riding and seat better? I cranked on them for all I was worth with a 8" hex wrench and got them as tight as I could, yet they are still about 1/4" out farther on either side of the bottom bracket then the old ones where. I don't want to go back to the SunTour cranks, these ones are way lighter and nicer looking, plus they have removable chainrings. What should I do?
12-10-03, 06:39 PM
Either get a shorter BB or readjust your front der to make it work. I suggest the BB.
can't you just adjust the limiting screws on the front derailleur?
Yes, you can readjust your front derailleur limit screws, but your chainline is now offset, which will make some of your large or even middle chainring / mid-to-large cog combinations unusable. Also, if the cranks do not seat properly onto the spindle, the assembly is weaker than it should be, and your knees may be sensitive to the wider splay of your pedals.
Although all square shank crank spindles use the same 2-degree taper, there are two different standards (originally Shimano vs. Europe) for the size of the square cross-section at the end of the spindle. This may be a good opportunity to upgrade your BB cartridge.
It actually is a Shimano cartridge bottom bracket, it just dosen't seem to go on all the way, and it would be more then my limit screw, I would have to take the fr. derailer off and move it up a bit because the teeth on the large chain ring hit the cage on the derailer right now, may take it to the shop tomorrow and see what's up with it.
12-10-03, 11:37 PM
You're going to have to completely readjust your front derailleur. Limit stops and everything. Not impossible to do, but it can be one of the most frustrating adjustments to learn how to do properly (and well). The Barnett's Manuals listed at the top of this thread do a good job of explaining what you need to do. Also, check out www.parktool.com there is a "how-to" section an their website as well.
Adjusting the fr derailer isn't a problem, I can do that, it's just a major pain. I'm just concerned about the cranks not going on all the way and how much wear might be caused by having a screwed up chainline now.
12-11-03, 01:20 PM
there will be increased wear becuase of the angle that the chain is at. you need a shorter BB spindle, which means a new BB. They aren't all that expensive, like 20 bucks, but you will probably have to pay for an install unless you know how to do it yourself.
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