Bicycle Mechanics - Ultegra Crankset failure

Hi,

I've managed to blow out my Ultegra double 175 mm Crankset after only a year of riding (commuting)

Has anyone else experienced this kind of failure? (the splines ripped out)

I never saw this kind of damage back in the olden days (square BB spindles)

Grrr.

Thanks,
Tom

This is not a common occurrence but can happen anytime the cranks are not torqued on correctly or are not maintained properly. I don't know your specific case; it may be manufacturer related, but I would think not.

The square taper joint also experienced this if overtightened(it would flair/deform the alu, making a proper fit impossible and always requiring overtightening until the cranks were no longer useable), or undertightened(cranks came loose, moving on steel bb axle and deforming alu crank arm, ruining the crank).

It's kinda like the porridge in the three bears story...it has to be "just right".

The cranks are aluminum alloy, tough but no match for the steel BB axle, so if there is a slight mal fit or looseness in the fit the axle chews up the crank. I
discovered this in an early install of the splined BB/crank. Crank seemed ok and to be tight and at the start of the ride ok, but as the ride went on the L
crank got loose and last 4 miles was just freewheeling around the BB axle. Tried to tighten with Alien tool which has 8mm allen but unable to adequately
torque and it loosened in less than half mile. Made it home with R leg only,
quite a workout! I would have had to walk if it were the R side. About 1/3
of the depth of the splines was chewed up. Torqued it on properly and it has
functioned fine since. Only one of my three road bikes with splined BB did this.
Steve

I had one non-drive side crank arm split at the bottom bracket connection but I agree with the others on the spline issue, it must have not been torqued correctly and came loose.

I agree it's an issue of poor/careless installation...I should know, I damaged mine by putting them on in haste one morning minus a steel washer behind the bolt head...bolt head 'ate' into alloy crank a little bit causing loss of tension on the bolt and it damaged the splines a little.

I put a washer in there and tightened both sides right up and they are fine to go stomping on...but still have some slop which is noticeable if bunnyhopping potholes. Annoying but I can live with it...my own fault. Pretty sure there is a very mild taper on the smooth cylindrical part of crank that provides most of the mounting surface...ie. bolt torque is pretty important. They need to be treated with a little more respect than probably everyone gave them when they first came out, IMHO.

Ah well...

Ended up purchasing a new crankset, and installed the crank last night...rides great, but I'm still a little unhappy that I wasn't informed by the bike shop that problems were occuring (which leads me to believe that they only tightened the allen bolt, and didn't pull the crank)

Oh well...one extra mark on my experience stick.

Thanks,
Tom