Results 1 to 4 of 4
  1. #1
    RoadBikeReview Member
    Reputation:
    Join Date
    Aug 2011
    Posts
    39

    Crankset/BB problem?

    I understand cassettes can wobble a little when spinning with no resistance, but what about cranks? Basically, I put my bike on a trainer and then I spun the pedals with my hand with no resistance on the rear wheel, it appeared that there was some wobble in the chainrings. Is this normal, or does it represent an issue with the BB or crank?

  2. #2
    RoadBikeReview Member
    Reputation:
    Join Date
    Feb 2002
    Posts
    18,978
    Quote Originally Posted by tanksl View Post
    I understand cassettes can wobble a little when spinning with no resistance, but what about cranks? Basically, I put my bike on a trainer and then I spun the pedals with my hand with no resistance on the rear wheel, it appeared that there was some wobble in the chainrings. Is this normal, or does it represent an issue with the BB or crank?
    Grab the cranks at the pedals and try to work it back and forth in the frame. There is likely no movement. What you are seeing with the chain ring movement is more likely a slightly bent chain ring or one or more of the crank arm spiders being slightly out of line.

    Hold a small screwdriver or other short, pointed object against the seat tube so that the tip just grazes the crank spiders as they pass. If the spiders are bent, you can even them out as follows:

    Place the bike on its side with the crank supported on a block of wood at the axle. With another block of wood or a stout dowel placed at the end of the offending spider(s) give it a whack with a hammer. Check for change in alignment. If you got no change, hit it harder next time. Repeat until all the spiders are even. You may need to bend them away from the frame (brace the right crank on the block of wood) or toward the frame (brace the left crank).

    Once the spiders are even, check the chain rings with the same technique except put the point of your screwdriver at the teeth of the rings (most likely the big ring only if the spiders are even). Straighten the chain ring by placing a large adjustable wrench over the ring with the jaws adjusted for a slip fit over the ring. Bend gently, and check alignment. Repeat until you've got it right.

    Even with the chain rings dead straight, you still will get some deflection due to pedaling forces, but that should greatly improve your situation.

  3. #3
    RoadBikeReview Member
    Reputation:
    Join Date
    Aug 2011
    Posts
    39
    Kerry, thanks. I tried your initial suggestion, and as you said there was no movement. So BB is okay. I kept an eye on the the chainrings as I rode today and they seemed to be pretty much straight once there was tension in the chain. In any case, the rest of what you suggested, though detailed and I'm sure fool-proof, is something I'd never try at home. I'll do anything to a bike that requires a hex wrench, but the LBS will be involved with anything else at this stage in my career as a mech. Will drop in to the LBS next week on a ride and see what they think. Best

  4. #4
    RoadBikeReview Member
    Reputation:
    Join Date
    Feb 2002
    Posts
    201
    i have had issues at time with loose chainring bolts. torque em.

Similar Threads

  1. Sram Red Crankset problem
    By comer7874 in forum Components, Wrenching
    Replies: 4
    Last Post: 07-29-2011, 08:43 AM
  2. TREK 800 Crankset Problem
    By parnavaz in forum Trek
    Replies: 3
    Last Post: 04-23-2011, 06:43 AM
  3. crankset problem or front derailleur?
    By fireplug in forum Components, Wrenching
    Replies: 6
    Last Post: 02-10-2011, 07:24 AM
  4. Crankset problem...any advice?
    By seemana in forum Components, Wrenching
    Replies: 13
    Last Post: 06-10-2010, 07:38 AM
  5. Problem installing a GXP crankset
    By MIN in PDX in forum Components, Wrenching
    Replies: 4
    Last Post: 06-16-2008, 11:20 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Sea Otter Classic

Hot Deals

Contest


Latest RoadBike Articles


Latest Videos

RoadbikeReview on Facebook