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Old 10-21-07, 12:23 PM   #1
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truvativ isoflow cranks w/ powerspline bb = defective?

Hello. I've got truvativ powerspline bb on my bike with truvativ isoflow crankset, 22-32-44.

I have read up on problems with this setup and several others have experienced my problem: my left non-drive side crank comes loose if you breathe on it and now I fear I have alignment issues due to riding with the loose crank (during the time I didn't know it was loose).

I've attached some pix, pls. note the edges of the splined bb, some deformation appears to have taken place and the edges are rough to the touch. I'm guessing this is causing the crank to come loose even faster than before, vicious circle...

Questions:

1. Any way to keep the crank firmly affixed considering the damage? I'm guessing the deformations at outer tip of splines are allowing play, no matter how much I tighten down. Blue loctite?
2. Anyone know if SRAM ever recalled the Truvativ ISOFlow MTB crankset? (I ask this question b/c others have asked it before and I never found an answer. I've got a call in to SRAM)
3. Why is the outer area of the crank hole threaded (see pic) when the bolt that affixes is completely smooth where it contacts those threads (see pic)?

Thanks



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Old 10-21-07, 03:43 PM   #2
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The threads are for a crankpuller. did you force this arm off without one? or did it just kinda come off easily? Im just curious. I think your left arm is toast regardless.
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Old 10-21-07, 03:54 PM   #3
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An aluminum crank arm won't damage a hardened steel spindle so I expect the spindle was defective as made. Follow up on your contact with SRAM.

As noted, the threads are for a crank puller which is a screwpress. The outer shell threads into the crank arm where you indicate and the center bolt pushes against the end of the spindle to pull off the arm. It should be necessary to use one if the crank fits properly.
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Old 10-21-07, 04:46 PM   #4
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The threads are for a crankpuller. did you force this arm off without one? or did it just kinda come off easily? Im just curious. I think your left arm is toast regardless.
thanks. no crank puller needed. that arm literally fell off when I first removed it
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Old 10-21-07, 04:48 PM   #5
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Originally Posted by HillRider View Post
An aluminum crank arm won't damage a hardened steel spindle so I expect the spindle was defective as made. Follow up on your contact with SRAM.

As noted, the threads are for a crank puller which is a screwpress. The outer shell threads into the crank arm where you indicate and the center bolt pushes against the end of the spindle to pull off the arm. It should be necessary to use one if the crank fits properly.
thanks, so I need a new powerspline bb and possibly a non-drive crankarm as well?

cheers
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Old 10-21-07, 05:12 PM   #6
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thanks, so I need a new powerspline bb and possibly a non-drive crankarm as well?

cheers
That's my take. I hope SRAM makes good on this problem.
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Old 10-21-07, 06:51 PM   #7
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There is nothing wrong with your BB or crankarm. Put the crankarm back on, tighten the crankarm bolt good & tight. If it doesn't wiggle, ride it. Powerspline is splined BB that just slides on, it is not a tapered fit. You can't ruin them by riding them loose like square tapered. I have a Powerspline with a ton of miles on it, the arms just slide on/off. On Truvativ's external BB/crankarm setup, the fixing bolt on the non-drive side tends to loosen easily as well, you just need to check & tighten if needed every month or so.
The outer threads are for dustcaps if you have normal bolts holding the crankarms on.
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Old 10-21-07, 10:25 PM   #8
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There is nothing wrong with your BB or crankarm. Put the crankarm back on, tighten the crankarm bolt good & tight. If it doesn't wiggle, ride it. Powerspline is splined BB that just slides on, it is not a tapered fit. You can't ruin them by riding them loose like square tapered. I have a Powerspline with a ton of miles on it, the arms just slide on/off. On Truvativ's external BB/crankarm setup, the fixing bolt on the non-drive side tends to loosen easily as well, you just need to check & tighten if needed every month or so.
The outer threads are for dustcaps if you have normal bolts holding the crankarms on.
Thanks, I remember before removing anything I checked whether the powerspline bb required a crank puller and was relieved that it did not.

As you note, I have been tightening and riding, tightening and riding. Only problem is that the crank arm is coming loose more often now. At first it was every week or so, now it is after every ride. I will attempt to tighten it down with Superman force next time and see what happens, but I have a bad feeling about this -- the frequency of the problem is alarming.
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Old 10-22-07, 08:16 AM   #9
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There is nothing wrong with your BB or crankarm.
I don't think so. Unless the OP has been tightening the crank bolts only finger tight, I think the crank arm is hosed. It's coming loose every ride and the splines have to be damaged by now.
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Old 10-22-07, 10:17 AM   #10
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On Truvativ stuff, I generally have to use a hex wrench with my 1 1/4" Craftsman combo wrench (it is like 18" long!) laced over it for extra leverage to tighten the non-drive crankarm. Anything less and the bolt will back out on me. It only requires a hex wrench to remove, no extra leverage.
Check the other thread "Crank Bolts", same response, different poster.
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Old 10-22-07, 10:47 AM   #11
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I had my splined truvativ compact double loosen like the op after only ~200 miles of use. i didn't have a 8mm (i think) to tighten it, so my wife picked me up for "the drive of shame." I just put on some non-permanent locktite on it, and it's been ok for the subsequent ~400 miles. Like the op, the crank arm just slid right off without the bolt in place, hopefully this, indeed, doesn't need to be press-fit!
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Old 10-22-07, 11:22 AM   #12
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OK, I'm going blue loctite and will tighten with Herculean effort

cheers
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Old 10-22-07, 03:25 PM   #13
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Make sure the crank arm isn't sitting at the same plane as the BB spindle face. If so, the crank arm has spread and bottomed out. No amount of bolt torque will keep it from rattling.
Can't tell from the small pics.

Another trick is wrap the bolt threads with some teflon plumber's tape. That will keep it from backing out too.
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Old 10-22-07, 07:45 PM   #14
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Make sure the crank arm isn't sitting at the same plane as the BB spindle face. If so, the crank arm has spread and bottomed out. No amount of bolt torque will keep it from rattling.
Can't tell from the small pics.

Another trick is wrap the bolt threads with some teflon plumber's tape. That will keep it from backing out too.


thx, I've got teflon tape, I'll try that first.

re: your comment on crank arm positioning relative to BB spindle face, not sure I understand what I should be looking for there?

thx
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Old 10-25-07, 04:26 AM   #15
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The aluminum arms should seat in the ISIS splines and have the end of the spindle below the flat of the arms where the bolt rests on. If the arms are deformed, and the spindle comes up to the flat, then the bolt can't clamp the two in tension.
From your pic, the spindle appears to be 1 mm below.
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