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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 06-15-08, 05:26 PM   #1
Roasted
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My 3rd gear on crank appears to be rubbing my frame...

http://s2.photobucket.com/albums/y36...t=P1070156.jpg
http://s2.photobucket.com/albums/y36...t=P1070158.jpg

As you can see in the 2nd pic, it appears as though I do have some room in between that gear and the frame. However, the 1st picture shows some sort of wear.

I like to stay in 21st gear as much as I can, so there's quite a bit of torque to be dealing with there. I can see, based on looking at how the chain stays centered in between my front derailleur, that when I crank hard on the right side, my 3rd gear on the crank tends to sway a little bit. Not much, but just enough, I suppose. But it only does it when I'm in that 3rd gear... I guess because the 3rd gear is farthest away from the bracket, so it is under more pressure when I pedal with a decent amount of torque.

I guess in reality there's nothing I can do here. It's not like it's a brand new bike... it's a 2004 Giant Boulder SE. Fantastic bike, for me, but at the same time maybe when I get rich and famous I'd like to get on a G Fisher Mullet, or something of that sort.

Anyway, what do you guys think?
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Old 06-15-08, 05:41 PM   #2
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Chainwheels do flex side to side under load. With an Al frame that is an alarming
amount of wear but your first pix seems to show the wear area a bit outside the
diameter of the chain ring. You might carefully smooth the rough area and put a
piece of thick tape there as a wear indicator (tennis racket wear tape is one
option) and see if the tape gets nicked in the course of riding over the next few
rides. If it does then something needs to be done. BB may have shifted to the
L, (unlikely) or been assembled backwards at some time. Or the CW may be a
sub that is larger than OEM hence the reduced clearance. You might consider
a 2 tooth smaller CR which would be ~3/8" smaller diameter. Spacers under the
R BB cup can move the BB to the R also.

Last edited by sch; 06-15-08 at 07:00 PM.
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Old 06-15-08, 05:47 PM   #3
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That gouging is probably the result of chain suck.
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Old 06-15-08, 06:24 PM   #4
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Maybe it was due to my bottom bracket. It was in bad shape. I ended up having a reputable bike shop replace it about a month ago. I mean, I have wrecked a few times on it... so maybe a rock or something hit it perfectly and caused the paint wear. Who knows...

I've only had it on the trail once since then + taken it on a 15 mile road ride. It's definitely 100% better than before, so perhaps it was due to the previous state of the BB that caused that?

I'll take your advice and put some kind of tape on it and monitor it. Thanks for the tip.

Also - roadfix... chain suck? ...??

Last edited by Roasted; 06-15-08 at 06:29 PM.
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Old 06-15-08, 08:15 PM   #5
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Maybe the LBS put in a slightly longer BB because of the damage?
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Old 06-15-08, 08:32 PM   #6
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Quote:
Originally Posted by Bill Kapaun View Post
Maybe the LBS put in a slightly longer BB because of the damage?
Or they put in a slightly shorter one, resulting in the damage seen.
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Old 06-15-08, 08:56 PM   #7
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Ehh, I doubt it. The wear that you see looks as if it has been there for quite a while. It doesn't look like fresh marks at all. Maybe I could take it in and mention it to them, but the above poster was right... the damage is extended out of the range of the 3rd gear being able to hit it.

I wonder if it was, though? I wonder what their response would be if I brought it in to mention it to them...
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Old 06-16-08, 02:33 AM   #8
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"Maybe it was due to my bottom bracket. It was in bad shape"
If the bearings were bad, it could have EASILY had enough slop in it to rub that much.

Expecting the LBS to remember back a month during their busiest time of the year may be asking a bit much!
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