Help with chainset replacement and bb spindle width...
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Author:  lclements [ Tue Nov 30, 2010 7:26 pm ]
Post subject:  Help with chainset replacement and bb spindle width...

Hey all,
I recently bought a shimano altus chain set from the retro mtb section and it has ended up going on my fathers bike. It is to replace his cheap shimano tourney FC-TX71 chain set. Got it fitted no problems, but when trying to set up the gears the dérailleur actually will not reach far enough to engage the outer ring.
So I figure a new BB will be needed with a shorter spindle. Is this correct or is there something I'm missing?
The tech docs for the old chainset can be found here, and although I cannot find the tech docs, the replacement altus is a FC-MC16

Thanks in advance,

Author:  sex one [ Tue Nov 30, 2010 7:35 pm ]
Post subject: 

on the front has 2 screws...marked H/L undo the H screw until it works..but not too far that the mech can push the chain over and off the big ring....if that fails then its a shorter axle bb time

the H and L are the limits to what the mech can shift to...normally just playing with these can sort it.

Author:  lclements [ Tue Nov 30, 2010 7:43 pm ]
Post subject: 

Yea, ive slackened both screws off as much as they can go, tightened the cable and moved the dérailleur down as the new chainset has smaller teeth counts...
How do I work out what length I need?


Author:  sex one [ Tue Nov 30, 2010 7:50 pm ]
Post subject: 

did you get a bb with it?

what size is the bb shell..should be either 68mm or 73mm

if you are using the original bb thats already on the frame, then its something to do with the chainset....square taper cranks i guess?

Author:  lclements [ Tue Nov 30, 2010 8:11 pm ]
Post subject: 

I didn't get a bb with it, it's just an old spare chainset that someone had.

I believe it's a 68, and has not that long ago had a new bb fitted by my lbs. cartridge, shimano but the left cup goes a long way into the frame (apparently the lbs didn't have any of the right length and put this shorter one in... so maybe the frame is meant for a 73...)

What do you mean square? As opposed to diamond? I thought square and diamond were the same taper, just different rotation of hole.

Thanks for the ongoing help,

Author:  sex one [ Tue Nov 30, 2010 8:21 pm ]
Post subject: 


there are a few different tapers..square/isis/octalink..but im guessing as you mentioned diamond thats its square.

the bb shell width is the measurement from one side of the frame to the other...where the bb goes in..

have you got any pics?

Author:  lclements [ Tue Nov 30, 2010 8:26 pm ]
Post subject: 

Right, i'm not sure whether it's square or diamond, but it's definitely not an exotic one like isis or octalink (I've never had them so they are 'exotic' to me)

As for width, it must be a 73 shell with a 68 bb as the cup sits a fair way ~5mm in the shell, which fits with the short bb replacement story from lbs.

Does the wrong bb width affect the chainset issue though, as surely its the left hand side that would have a odd axle length. As it is, the left is fine as the lbs put one with a long enough axle to clear the frame.


Author:  sex one [ Tue Nov 30, 2010 8:35 pm ]
Post subject: 

it sounds that what they've done is...put in the right sized bb...but one with the wrong length axle as there are a few lengths to choose from..have you got the tools to take it out?..failing that, measure the axle length.

Author:  lclements [ Tue Nov 30, 2010 8:39 pm ]
Post subject: 

Ok, surely the fact that the left cup is way into the shell means it't the wrong width?
Also it was working fine with the old chainset (the rings are worn out hence the replacement), so is it a case of the old chainset being odd?


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