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PostPosted: Wed Jun 19, 2013 8:05 pm 
Devout Dirtbag

Joined: Sun May 19, 2013 10:04 pm
Posts: 115
Managed to shred the thread in my truvativ 5 d crankarm (pedal works loose)

Managed to get hold of a truvativ hussefelt pair of arms for next to nothing that will do the job....well they would but my bb is square taper ,,

What is the best option for me, needs to be cheap as possible really,

The bikes an 03 firemountain, will an isis bb fit?, if so what size would I need?

Thanks in advance


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PostPosted: Thu Jun 20, 2013 11:07 am 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
Posts: 8202
Location: New Forest, UK
An ISIS will fit, just be aware that they undersized all the bearings in these type systems so they have pitifully short lives...which is why the cranks are cheap.
It'll be a 68mm shell.


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PostPosted: Thu Jun 20, 2013 11:22 am 
Devout Dirtbag

Joined: Sun May 19, 2013 10:04 pm
Posts: 115
Thanks, I take it I need one with the same or similar length spindle aswell? Will the crank arms sit on the spindle/shaft in a similar position to the arms on a square taper drive?

It's a shame about the lifespan but got to try and get it on the road fairly cheaply, either that or a square fit crankset but think ill get the isis bb cheaper


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PostPosted: Thu Jun 20, 2013 11:35 am 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
Posts: 8202
Location: New Forest, UK
You need the width to match the crankset, not the bike. Sorry, I don't know the dimension as I've always avoided ISIS and Octalink.


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PostPosted: Thu Jun 20, 2013 11:58 am 
Retro Guru
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Joined: Thu May 03, 2012 7:13 pm
Posts: 2574
Location: The Cock Inn, Tillett, Herts
Hamsters right - isis and octalink bearing can be shocking because they're so small, which is a shame because Octa especially gives a good and stiff crank to shaft interface. Cheap bearings will die quickly, so it pays to spend out on decent ones...by which time you could've bought a square taper crankset.

As an aside the manufacturers didn't learn from this, and most external bearing bb s not only suffer with small and puny bearings but are also in the line of fire from the front wheel, so are virtually a consumable item these days :(

Anyway, cheap bb is gonna ultimately cost you dear.


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PostPosted: Thu Jun 20, 2013 2:05 pm 
Retro Guru
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Joined: Sun Mar 14, 2010 2:33 am
Posts: 2918
Location: daaan saaaf
Quote:
As an aside the manufacturers didn't learn from this, and most external bearing bb s not only suffer with small and puny bearings but are also in the line of fire from the front wheel, so are virtually a consumable item these days


Seems to be the case, my external type bottom bracket has some play in it after about 1,200 miles, whereas the UN72 square taper BB in my other bike has probably done double that and is still as smooth and play free as the day it went in. Shame they don't make the UN72 any more, but the UN54/55 seem to last just as well.


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PostPosted: Thu Jun 20, 2013 3:05 pm 
Devout Dirtbag

Joined: Sun May 19, 2013 10:04 pm
Posts: 115
When you say match the crankset not the frame in regards to what?, an I looking for how far the splines sit into the arms ? Surely I would be looking at total width so the chain line lines up??


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PostPosted: Thu Jun 20, 2013 3:27 pm 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
Posts: 8202
Location: New Forest, UK
Each crank design needs a matched BB to get the chainline right. A quick Google of "truvativ hussefelt bb length" suggests 113mm.


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PostPosted: Thu Jun 20, 2013 3:54 pm 
Devout Dirtbag

Joined: Sun May 19, 2013 10:04 pm
Posts: 115
Nice one cheers, the square taper that came off was about 113mm also.

Sorry about the daft questions, I take it most cranksets measure the same at the chain rings, but because of different fittings etc require different length shafts to achieve that width?


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PostPosted: Thu Jun 20, 2013 8:52 pm 
Retro Guru
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Joined: Fri Jan 12, 2007 1:32 pm
Posts: 1953
Location: Staffordshire
From experience, Octalink seemed ok from a longevity point of view but ISIS seemed really bad especially Truvativ ones even the more expensive ones.

My external HTII's have been pretty good apart from the Deore one I had. The XT and current Saint one have been great. My Saint one is over a year old and is still really smooth despite the nasty summer we had last year.

Most modern four bolt chainrings will be the came (104bcd) but as with all things standards are getting twisted at the mo.


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