Crank arms moving sideways, why? Video attached

Triathlon Forum
1

So, being a noob around bicycles I need help with something. All of the sudden I wasn’t able to shift gears onto the bigger chainring, so I had a look to see why. I noticed that the crank arms are quite loose, as in where they both connect to the frame. (Sorry for the poor explanation!) which results in them moving sideways basically, so naturally the derailleur isn’t able to move the chain as it should. I realized I wouldn’t be able to explain exactly what’s happening, so I’ve uploaded a video clip on youtube:

http://www.youtube.com/watch?v=SFR7A0Lmdf8

Would really appreciate it if anyone could tell me what I can do to sort this out. Thanks, from a non-biketechnician.

2

When you move one side does the other move with it? If not I would say that you just need to tighten them down.

If they move together then your bottom bracket is likey shot.

3

Looks like you need to tighten your crank bolt. Look up the instructions for installing your particular crankset.

4

tighten your crank arm.

Looks like an Ultegra crank? (shimano crank anyway).
There are two bolts opposite of each other in the 9 and 3’o clock position when you face the crank arm from the sides.
Tighten those equally.

5

I had this exact same thing happen to me. Easy, easy fix. Your crank arm is loose as is slowly falling off. If you don’t tighten, it is only going to get worse. The “trick” is that you have to loosen it before you tighten it so that you can slide the arm back where it needs to be. So, on the crank arm, there should be two bolts. Loosen those up. Once loosened, the arm should slide up flush with the bottom bracket. Then wrench those bolts back down. You really gotta tighten them. I don’t know what the torque setting is but you should really be able to put some muscle behind it.

6

I had this exact same thing happen to me. Easy, easy fix. Your crank arm is loose as is slowly falling off. If you don’t tighten, it is only going to get worse. The “trick” is that you have to loosen it before you tighten it so that you can slide the arm back where it needs to be. So, on the crank arm, there should be two bolts. Loosen those up. Once loosened, the arm should slide up flush with the bottom bracket. Then wrench those bolts back down. You really gotta tighten them. I don’t know what the torque setting is but you should really be able to put some muscle behind it.

Yes as other folks keep telling you the pinch bolt(s) on your left crank arm need to be tightened.

And as posted above you need to loosen the pinch bolt(s) first to snug the crankarm back down. There should also be an endcap in the left crank arm that is used to set the bearing preload before tightening down the pinch bolt(s). You may have already lost this preload cap but depending on the make and model of your crankset it looks something like: http://www.chainreactioncycles.com/Models.aspx?ModelID=5095 and is adjusted for proper bearing load with a tool that looks something like: http://www.outsideoutfitters.com/p-1094-shimano-hollowtech-ii-crankarm-cap-tool.aspx?variantID=12531&gclid=CPTTpqPA0rgCFcN_QgodPFwAHw

So you basically:

  • Loosen the pinch bolt(s) on your left side crank arm
  • Slide the crank arm on so there’s no visible play
  • Screw in the adjuster cap bolt that fits your crank and screws into the large hole in the left hand crank arm
  • Use the preload adjuster tool (some designs use a very large hex key) until there lateral play is eliminated but don’t crank it down super had and squeeze the bearings
  • Tighten the pinch bolt(s) on the left hand crank arm

Do it soon or you’ll likely lose the crankarm while out on a ride and you may damage the splines so it’s hard to get the crankarm back on or damage the splines in such a way that the crank is never tight again and always has some residual play.

When in doubt, surf over to the Park Tools website where repair info for things like this and other bike maintenance is available: http://www.parktool.com/blog/repair-help

Good luck,
-Dave

7

Dave Ryan’s instructions are great. Just to add to them, the “usual” (I know for a DA crank, suspect the Ultegra is the same), the torque on the pinch bolts is between 12-14Nm.

8

I had this happen on my Salsa Fargo. I guess I didn’t tighten the pinch bolts tight enough and the crank slid out. It was really odd feeling before I realized what had happened.