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PostPosted: Tue Sep 11, 2012 11:05 am 
Dirt Disciple

Joined: Mon May 07, 2012 11:50 am
Posts: 26
Location: Oxfordshire
Hi all

I have just aquired a GT Agressor 3 which I believe is a failry new model. It has a cheap front mech and a square taper bottom bracket.

The front mech is one that is held in place with the bottom bracket so I was going to replace the bottom bracket with an octalink one and a Deore crank and rings that I have spare, and a Deore front mech.

The octalink bottom bracket I fitted seems a little close to the frame on the chainring side. I have never fitted it to anything before so I am not even sure if it is a mountain bike one and the smaller ring has scraped the frame (which is a shame). I fitted the old square taper bottom bracket with the Deore front mech and the non-chainring side seems a little proud of the frame now as I am not using the old cheap front mech bracket. So basically I am looking for some advice.

Will any Bottom bracket work with a bottom bracket mounted front mech or are they wider than a normal one? Is the octalink bottom bracket I have just too short or am I missing a trick here somewhere?

If I do have a short octalink bottom bracket and just need a slightly longer one, does anyone have one for sale?


Thanks all


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PostPosted: Tue Sep 11, 2012 11:31 am 
retrobike rider
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Joined: Thu Oct 14, 2010 1:33 pm
Posts: 3973
Location: Brighton
you'll need to measure the spindle length of the old one that fits.
the BB mounted mech is an E-Type mech. this just has a space created on the outside of the BB shell for it to fit. this doesn't relate to axle length (i don't think) and as far as i am aware, you can fit an e-type BB and use a seat tube mounted mech instead without an issue.
just make sure the spindle length (axle length of the BB) is correct.
sounds like you may need a longer one.
you may be able to use BB spacers, but without pics i'm unsure. also, with it being a GT, there may be something i don't know that a GT nut on here does. i'm sure one will pop along soon to correct me if needed :)


hope that goes someway to helping!


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PostPosted: Wed Sep 12, 2012 6:39 am 
Retro Guru

Joined: Mon Jun 04, 2012 10:02 am
Posts: 441
Location: Australia
Might sound silly but check if it fits other way around.

Usually one side sticks out more than the other.

Hmm.. the the net hasn't been much help for the BB spec.

Does the axle lengths of the old one match the old?


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PostPosted: Wed Sep 12, 2012 9:10 am 
Dirt Disciple

Joined: Mon May 07, 2012 11:50 am
Posts: 26
Location: Oxfordshire
Bloody hell you get up early!

Anyway, I see what you mean about turning it around, but the threads are different rotations on either side. Do the threaded bits come off? The one on the non-chainring side does, but I was't sure about the other side.

I haven't actually measured ther old or the new lengths yet, but I will later this evening.


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PostPosted: Thu Sep 13, 2012 12:00 pm 
Dirt Disciple

Joined: Mon May 07, 2012 11:50 am
Posts: 26
Location: Oxfordshire
OK, had a look and I think I get it. The old bottom bracket didn't have any markings on it but I had another square taper bottom bracket which is a 68mm with a 122 spingle. The octalink I have was a 118 and is a lot shorter on the chainring side than the original square taper one.

So I have ordered a 128 octalink which should put the chainrings a good distance from the frame. Also the old original bottom bracket was 73mm (I think) so I have ordered the same as I want the option to use a bottom bracket mounted front mech if I want to.

Unless I am conpletely wrong...


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PostPosted: Fri Sep 14, 2012 7:40 am 
Retro Guru
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Joined: Thu Sep 04, 2008 12:23 pm
Posts: 1224
Location: muddy, grimy yorkshire :D
What width is ur BB shell? It's either 68 or 73mm and you need the correct BB for your frame. If you're mounting a BB mounted front mech, you need an E-type octalink BB.


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