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Discussion Starter · #1 ·
I've been using titanium crank bolts for the past 3 years, as well as an ISO (square taper) bottom bracket with a titanium axle. I've been using Loctite Anti Seize compound to prevent galling, and have had absolutely no problems with this combination. Until this month, that is.
I have begun to have a problem where the crank bolts, and especially the left side crank bolt, start to loosen as I ride.
I DID try thoroughly cleaning all of the threaded surfaces and applying Loctite Blue before re-assembling, but that didn't help at all. The left side crank bolt again came loose just 30 minutes into my ride.
I am confused as to why this is occurring, as the bolts remained perfectly tight for the first
2 1/2 years of use? Any ideas?

Thanks. :)
 

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Generally, crank bolts on square taper cranks loosen because torque during the crank installation was insufficient. The bolt actually doesn't turn, but the insufficiently tightened crank moves up (into the frame) on the axle taper as you ride. As it does, pre-load on the bolt is reduced more and more.

I wonder if the Loctite Blue prevented you from getting sufficient torque or gave you a false torque reading during the crank installation or crank re-tightening? I'd take it all apart again, clean off the Loctite, apply grease or anti-seize and torque to specifications.
 

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likes to eat donuts
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Discussion Starter · #4 ·
the problem continues

I have done as wim suggested. I carefully and thoroughly cleaned the threaded surfaces, applied Permatex Anti-sieze, and torqued to the proper specifications. After a one hour ride, both crank bolts had loosened significantly, especially the bolt on the left side. I re-torqued, rode again for about 1.5 hours, but again found that the bolts had loosened.

What I'd really like to understand is why these bolts are now failing after 2.5 years of successful use? frdfandc had previously mentioned stretched threads. Is this at all a possibility? I'd assumed that the ti bolts would be less prone to streching than the stock steel bolts.
Thanks.
 

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'brifter' is f'ing stupid
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if the bolt got loose one time...and you rode w/ the bolt AND the crank arm loose...the problem is most likely not the bolt at this point, it's more likely the crank arm. the square taper hole is probably not "square" anymore from riding the bike w/ the arm loose. if this is the case, (you can usually tell by looking at the inside of the hole) that crankarm will NEVER stay tight again. you can get it as tight as you want, but it will loosen up because the hole has a slight twist to it.
you weren't using the ti bolt to actually tighten the crank arm down were you? we always used a steel bolt to push the arm on, then put the ti bolt in and torqued it down.
 

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likes to eat donuts
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Discussion Starter · #6 ·
thanks

I still have a lot to learn as a mechanic, apparently. I DID tighten the crank to the BB using the ti bolts, not knowing otherwise, and I am pretty strong feeling that the square hole in the crankarm has worn, and is now not exacty square. I will check it later to confirm.
Does that mean that I've screwed things up here, and that I'll probably be buying a new crankset soon? Because that would suck. :(
 

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Try steel bolts. If they loosen up, the cranks are probably shot. Tell your wife you need a new bike. If they don't loosen up, your ti bolts might be stretching. If the diameter of the bolt looks "hour glassed" from top to bottom, they're stretched.
 

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'brifter' is f'ing stupid
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do what test pilot said, if that doesn't work, follow his instructions. a new bike is the only cure to this problem :thumbsup:
 

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Yep! And not just any new bike. Only an expensive new bike will do.
 

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Unsafe at Any Speed
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wim said:
I'd take it all apart again, clean off the Loctite, apply grease or anti-seize and torque to specifications.

Anti-seize. +1 :thumbsup:
I sometimes wonder if grease permits good seating, initially at least.
 

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Off topic. But has anyone seen Ti bolts stretch?
 

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'brifter' is f'ing stupid
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reptilezs said:
crank arm interface is worn out from riding it loose, replace and next time torque it properly 30-35 ft lb
i might have mentioned that about 6 days ago...
 

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No, but I have seen mild grade steel bolts stretch...

"Commercial (99.2% pure) grades of titanium have ultimate tensile strength of about 63,000 psi (434 MPa), equal to that of common, low-grade steel alloys, but are 45% lighter.[7] Titanium is 60% more dense than aluminium, but more than twice as strong[7] as the most commonly used 6061-T6 aluminium alloy. Certain titanium alloys (e.g., Beta C) achieve tensile strengths of over 200,000 psi (1,400 MPa).[11] However, titanium loses strength when heated above 430 °C (806 °F).[12]" - from Wikipedia article which contains source references
 

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Just wondering. I've broken a few Ti bolts. They let go with a snap. No warning. No signs of streching when examining the failed parts. I've no idea what grade of Ti they were.
 

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Discussion Starter · #18 ·
Kerry Irons said:
You silly boy! To save weight, of course!
Yes, I used the titanium bolts to save a little weight. Although there is no obvious streching/damage to the ti bolts thread, they appear to have been the cause of the problem. I have now put the original Campy (steel) crankbolts back in using Permatex anti-seize, torqued them to 32 ft lb., and they have have not come loose since!.

As cxwrench had said earlier, I should have used the steel bolts to push the crankarms on, and only then replace the steel bolts w/ the ti counterparts. It appears as though the ti bolts threading was damaged by using them to directly drive the crank arms on to the b/b spindles.

Oh well, live and learn. I'm still saving for that expensive new bike, though! :thumbsup:
 
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