Bike Forums - External Bottom Bracket Problem

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External Bottom Bracket Problem

Today, while I was riding home, I started to feel a wiggle in my cranks, so I pulled over to check it out. I noticed that my crank arms were pretty loose and decided to walk the bike home. Once I got home I noticed that the 8mm bolt running through my external bottom bracket was lose. I remember tightening it only a couple days ago though.

Does anyone know what may have caused my BB/ Cranks to loosen on their own?

I have an external bottom bracket with Raceface Cranks.

Figure B shows the bolt that came lose to a point where there was no resistance. I ended up tightening that bolt back up, but if I tighten it too much, the cranks start to resist on their own.

Figure A shows the two points where my cranks began to wiggle.

Any help or suggestions would be greatly appreciated.

http://i943.photobucket.com/albums/a...e85/Crank1.jpg

http://i943.photobucket.com/albums/a...eene85/BB1.jpg

Seems newer cranks require repeated tightening after initially installing them.

I initially tighten them, ride 1 mile and retighten, ride 5 miles and retighten and check every 20 miles after that until they reach at least 2 checks that they have remained tight.

Quote:

Originally Posted by CB HI (Post 11009607)

I agree that this is true of square taper cranks, but these cranks appear to have a splined BB/crank interface, where this should not be the case. See the link in post #2.

Im not really sure what to be looking for in the link. I understand how to install and the mechanics of the system. Im just curious as to what could be causing them to loosen up on their own so quickly.

Maybe you should inquire in the bicycle mechanics forum. All my bikes have square taper cranks, except my new road bike has Dura Ace cranks with external bearings and a splined interface, except they use a different attachment method with a pinch bolt on the nondrive side, so I don't know what your problem might be. I do know that the bolts on square taper cranks have to be tightened a lot, about 33 ft-lbs, but I don't know what it should be in your case.

maybe it's the interface itself?

it says to grease and tighten to 61 newton/meters.
I've never had a problem with the arms loosening with my tiagra cranks.

@AEO - Actually, thats the torque value for the crank arm bolt, which works out to 45 ft-lbs, even more than I use on square taper cranks. My guess is the OP simply didn't tighten the bolt sufficiently to achieve that torque, which is pretty high. I copied the following notes from the instructions:

*NOTES:

1) Actual torque required to bottom-out RH crank may vary but this is a “hard stop” that will be very noticeable. It is not possible to “over-load” the bearings with the RH crank
installation. The most important thing is to ensure that the RH crank bolt is fully bottomed-out, regardless of final torque requirement.
2) After installing RH crank, spin the crank a few times hard by hand. The system should spin smoothly but some rotational friction from seal drag will be noticeable. This is normal and
will dramatically decrease after the first few miles of riding as the seals become lubricated and some BB assembly components seat-in.
3) Race Face Deus XC / Evolve XC / Ride XC - EXI cranksets feature the industry standard ISIS Drive spline for the interface between the RH crank arm and the BB spindle. All
standard procedures for installing and removing ISIS Drive cranks can be applied here.

4) Check crank bolt periodically (e.g. during routine bike maintenance) and re-tighten to 45 ft-lbs / 61 N-m / 620 kgf-cm as required.

very possible that I did not tighten enough initially. I hope that is the problem!

It sounds too me that a) I need to tighten the RH crank bolt all the way down to where it "bottoms out" and b) its impossible to over-tighten it. (which is strange because I've heard if you tighten it too much, there will be rotational friction.

Ill give it a shot though... thanks everyone!