Sheared Aluminum Crank Bolt - GXP crankset

[dhk2]

Just watched the video..well actually, I skipped ahead to the last 2 minutes. Those expansion cracks reminded me of a ride I did a few years ago on the Paul Bunyan and Heartland Trails up in central MN. We started in Brainerd, unloaded the bikes for four nights at Lake Walker where the trails intersect, and rode out and backs each day. Was a great, relaxing ride through the north woods,,....except sections of the trails had those cracks just like the road you were riding in the video. Those pounding cracks every 5-10 seconds get annoying, and really put a lot of stress on the fork, frame and wheels of a road bike.

 

[maydog]

The feedback is appreciated.

I suppose the stresses killing the bolt are not about the torque axis, instead being parallel to the axis. My left knee is rather stiff from arthritis and I may pedaling with some strange stresses on the left side which may accelerate the failure. Plus I am on the heavy side and put considerable miles on throughout a year.

The crankarm may be a bit worn as this is the only GXP set I have that has, yet, sheared a bolt. When torqued on, there was no noticeable play in the crankarm.

Still, the bolts are much cheaper than a new arm and I couldn't find a matching arm on ebay or elsewhere anyway. I believe that a stronger bolt should be able to deal with whatever stresses are killing the aluminum bolts. In a pinch, the bolts are field replaceable so I will carry a spare.

 

[CAMPYBOB]

Are you sure your old bolts are aluminum? Try a magnet on them?

I agree with your thoughts on side stresses from your pedaling style killing the bolt head. I exert side pressure on my cranksets due to a different pedaling form issue, but sufficient enough to cause the wave-washer end play click-tick in Campy Ultra Torque cranksets (see other thread I started if interested).

I would also think you some play in your crank splines and maybe it is working on the underside of the fixing bolt's head and causing it to pop.

 

[Volnix]

Originally Posted by maydog
My intention with this thread is to keep it on topic and informational in case someone else is having the same issues I have.

Lolololol, I dont have these "issues" for sure.

(Lololololololol, that's March???

)

 

[maydog]

Yes they are aluminum for sure. There was no noticeable play even under high stress.

I figure with a steel or titanium bolt that the crank will fail before the bolt - which is ok with me, because then I can be sure that the arm was the culprit and be rid of it.

 

[CAMPYBOB]

Good luck! I think a steel bolt will cure the head popping issue.

 

[maydog]

I found that the M15 capless crank bolts for an ISIS bottom bracket fit perfectly. I am still waiting on the titanium replacements, so this evening I went ahead and used the steel bolt. There is no way the crank is coming loose now, I used locktite on the bolt and FWIW I put a thin coating of JB weld on the spindle splines a bit back from the end. The epoxy may help fill any voids or play in the splines?

Even if the bolt goes now, the crank may stay in place. It may be a bear when/if I need to service the crank or bottom bracket, but this is my beater and I have already spent many times the bike's worth in replacing worn parts. I'll be happy if I can get even one more season out of it.

I'll swap out the aluminum bolts on my other bikes for the titanium ones when they arrive - sans the epoxy.

 

[CAMPYBOB]

I'll lend you my oxy-acetylene torch when it's time for a bearing swap.

A good hacksaw should get that arm off the spindle...or get you a two-piece spindle!

Your fix is still light years better than losing the left crank arm unexpectedly, losing control of the bike and sailing into oncoming traffic like I did when I broke a Super Record arm into two pieces. It can be very dangerous to lose a crank arm with zero warning.

 

[Subliminal-SS]

Have you tried checking the calibration on your torque wrench. I had the mis fortune of snapping my Brand New Chainring bolts because the torque wrench was out.

Its easy to calibrate or at minimum check with a Measuring tape Coat Hanger and about 30lbs in weights?