# Left crank, technical advise needed (please!)



## fish_on_a_bike (17 Apr 2009)

Helo all,

I have a 5-year-old bike with a Truvativ Firex crankset. The left arm has been a bit loose for too long now and needs replacing. It's square tapered and the crank arm 'square' is almost a circle due to a lot of riding.

I've searched all over the internet for one, and the only two options i have are 
Truvativ Firex Crank Arm, in either *GXP* or *ISIS*.

I've researched the meaning of these but still can't quite figure out wether or not either on will fit onto my square tapered fixing. Are *GXP *and *ISIS *alternatives to a square tapered? Is my square-tapered truvativ firex crank set out of date (thus, will I need to replace my whold BB, etc)?

I would be eternaly gratful to anyone who can make sense of this for me.

cheers


p.s.- in short I'm looking for a left crank arm to directly replace my old one, and it's doing my nut trying to find one, please help


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## Steve Austin (18 Apr 2009)

GXP and ISIS are very different fittings, so you want to find a new left arm with a squrare taper. You MAY be able to find a single left arm, or the alternative is to buy a new crankset.
Then you have two options, a whole new thing, with a new BB, that may be a new external BB system, or you just buy some new cranks arm that fit square tapers. Shimano Deore are good reliable and cheap


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## Mr Pig (18 Apr 2009)

I have a left crank here you can have if you want? It's silver and I think it's 175 long, I'd have to check.


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## Angelfishsolo (23 Apr 2009)

Is there a chance that if the crank has been loose for such a long time that the BB end will be worn as well?


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## peanut (23 Apr 2009)

Angelfishsolo said:


> Is there a chance that if the crank has been loose for such a long time that the BB end will be worn as well?



no its super toughened steel. You wouldn't make a scratch on an axle with a file or hacksaw. The aluminium is much softer so all the wear would be there


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## Angelfishsolo (23 Apr 2009)

OK Thanks, always better to be safe and sure 


peanut said:


> no its super toughened steel. You wouldn't make a scratch on an axle with a file or hacksaw. The aluminium is much softer so all the wear would be there


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## fish_on_a_bike (29 Apr 2009)

thanks guys,

i was at the LBS toady, i took the LH crank arm off to check the square (dimond or straight) and the crank screw came apart (half being stuck in the square tapered bit). I was planning on getting a new bottom bracket and chain set any way, this just made the process quicker.

I'm looking into it now. I'm looking for durabillaty over anything else, then weight. It seems the best way to go it an exterior BB. Does anyone have any advise on the best way to go? I've had truvativ and it has served me well, though I'm now looking at the SLX shimano.

All the advise I get here helps ma a lot. Very grateful, cheers


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## Mr Pig (29 Apr 2009)

Like I said, if you just want to replace the left crank I have one here you're welcome to. It's silver and 175 long.


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## RedBike (3 May 2009)

> I'm looking into it now. I'm looking for durabillaty over anything else, then weight. It seems the best way to go it an exterior BB.



The most reliable are still the square taper design. Bottom brackets 'normaly' always fail first and the square taper designs have large well sealed bearings. 

Isis have small bearings prone to failure. 
External beearing cups when used for MTBing are prone to getting water in.


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