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Ultegra splined crank loosening(7 posts)

Ultegra splined crank looseningkiwi_john
May 16, 2002 5:12 PM
My crank bolt came loose during a ride recently (I've only had the bike a few months), and hence the splines on the crank are slighly damaged and the crank now constantly creaks, especially if side pressure is applied to the crank arm.

Do you think I should replace the bottom bracket as well as the crank arm? Can I count on the fact the shaft is steel and the arm aluminium, or will there be microscopic wear on the shaft that could slowly ruin the new crank arm as well? The dark coating does show some wear on the tips of the splines and a little on the shaft itself, but I cannot see any deformation. Could I check for wear with calipers? Also, most people seem to recommend greasing the splines - how does this affect the interface fit?
re: This is only an opinion...Akirasho
May 16, 2002 8:44 PM
but the spline/BB interface is incredibly strong when it's properly fitted, and incredibly weak when it's not...

How much wear and tear the crankarms can take is beyond me... and I doubt that simple calipers would give an accurate enough measurment of tolerances (even if you knew what they were... which Shimano might not even give to shop wrenchs to protect their design...)

I'd try a bit of grease on the splines... perhaps a turn or two of teflon tape... crank interface at a different point so different splines alighn... retorque the cranks, then listen and watch... Worse case (aside from a failure out on the road) would be as you described... new cranks (not cheap)... and perhaps a new BB. On the other hand... this might "cure" your symptoms.

Also, don't rule out the possibility of the creaks coming from another area... saddle rails, seatpost, pedals, loose rings???

We abide.

Remain In Light.
Bolt security a likely problemCalvin
May 17, 2002 3:20 AM
It would be very surprising if the bottom bracket needed replacement. The spindle is bearing hard steel. Use a torque wrench in possible to secure the bolts, even now after the damage. If the bolts loosened, it is most likely because they were simply not secure when assembled. Now that the arm is damaged, the fit in compromised as you suspect. A new arm seems like the solution. However, you have nothing to lose in trying some retaining compound on the splines. It may not work, but it would be interesting to try. Shimano does recommend greasing the spline fit, but if you are sure the arm is creaking from damage to the fit, clean the splines and run with some Loctite RC680, or similar retaining compound.

As stated in other posts here, double check other area for the creak as well. See
Bolt security a likely problemcurlybike
May 17, 2002 3:36 PM
680?????? Wow, that is some pretty healthy stuff. Seems like you would start with a lower # than that. 242 is always a good place to start. With 680 he might have to use a puller plate to get the arm off after he pulls the threads out of the arm.
repair using retaining compoundkiwi_john
May 17, 2002 6:36 PM
Thanks for the retaining compond sugestion - a mechanical engineer at my work also suggested trying that.

How permanent are the retaining compounds - will I be able to remove it from the splines if it does not work?

Also, would 660 be more suitable than 680? 660 is listed as good for repairing damaged press fitted/mating parts with up to .02" gaps, whereas 680 is recommended for slip fitted cylindrical parts with gaps up to 0.015". I would guess that the depth of the wear would be close to these limits.

Thanks for the help everyone!
repair using retaining compoundcurlybike
May 17, 2002 6:52 PM
Most of the retaining compounds are very difficult to defeat. Some are listed as a substitute for welding! It is always best to use the mildest that will work.
Before you reinstall the crank arm.Spoke Wrench
May 17, 2002 5:14 AM
Take the self removing ring completely off. Make sure the crank splines are properly aligned and torque down the crank bolt. The last step is to spin on the self removing ring again.

The self removing Shaimno cranks are easily damaged by improper installation.