Take the 2-minute tour ×
Bicycles Stack Exchange is a question and answer site for people who build and repair bicycles, people who train cycling, or commute on bicycles. It's 100% free, no registration required.

I have a repair question. I am experiencing some slipping when I pedal, once-per rotation, however, it is not the normal chain/gear skipping that I have read about most of the time. The bike is an old steel frame Bianci, with 18 gears.

The slip is subtle, less than one chain link for sure, accompanied by no audible noise or jarring. I can only "feel" it through my feet in the pedal. Also, it does NOT have to do with how hard I am pedaling, if I pedal slowly while rolling so that its freewheeling, I can still feel the slip, which feels like a different "texture" while pedaling. I hope that makes sense, I cannot think of a better way to describe it. It seems to not happen all the time (about 80%), but I have not been able to correlate when it happens to a specific gear combination for example.

I tightened all the bolts on my chainring and in the rear derailleur, but that did not fix it. Does anyone have any idea what could be causing this?

Thanks for the help!

share|improve this question
4  
Have you checked the crank arm mounting bolts or the crank cotters (if it is old enough to have them). –  mikes Apr 30 at 10:28
1  
As @mikes suggests, it sounds like you have a crank arm that is slipping. If that is the case then by now the arm (and possibly the bottom-bracket shaft) is probably wrecked, but a skilled mechanic may be able to add shims to "rescue" the arm for the short term. –  Daniel R Hicks Apr 30 at 15:44
    
might be the a stretched chain skipping a tooth on the chain ring. –  Jeff Wurz Apr 30 at 21:47
5  
I used to get that when I had a bearing in the bottom bracket going bad. –  JohnP May 1 at 16:44
1  
Kink in chain? Try replacing or oiling the chain. –  Blam Jul 2 at 16:17

5 Answers 5

Drop the chain and try to rotate cranks. If "skip" feels then I would look into BB. If not, then pretty much sounds like kink in the chain which is very possible on very new or very old chains.

Very new chains can be over-pressurised while installing and therefore one link connection is just not flexible enough which makes it "skip" when going through the derailer. Old chains have rust and dirt problem which causes same problem.

share|improve this answer
    
I agree with this, it sounds like you've got a sticky link. Go through the chain and wiggle all of the links, I suspect you'll find one that doesn't want to move, and that's your culprit –  stranger Aug 1 at 13:28
    
This is indeed one possibility. What happens is that a couple of links are too tight toghether, so when they pass through the rear gears and the chain is curved, these links retain the angled position when they leave the rear cog. But right after that, the tension from the pedals straighten them out, producin this "less than one tooth skip". It can happen to a chain of any age that was installed with a chain cutter but was not "relieved" from the presure, or the chain link may have been deformed somehow. –  Jahaziel Aug 1 at 14:13

It sounds most likely that the pawls on your (assuming) freewheel are starting to go. These are the mechanisms inside of your freewheel that let it spin one way, but not the other. Sometimes a little grease may help, and sometimes you just need to get a new one. It's hard to check yourself though, because really the only way to narrow this down is to get another freewheel and try that one instead. You'll need specialty tools to do this.

share|improve this answer
3  
If it were the freewheel/freehub it would not be once per pedal rotation. –  Daniel R Hicks Apr 30 at 15:41
    
Or the free hub body is loose and therefore only partially engaging the teeth. –  Phil Willoughby Jun 22 at 18:18

There might be 1001 things, but here is one more: Maybe your pedal arm is bent therefor once per rotation it is touching the frame.

share|improve this answer

I would check the bull bearing for wear or lost balls. I had the same feeling once, and it was the bull bearing which cause this.

share|improve this answer
1  
What is the "bull bearing"? I'm not familiar with the term. –  Daniel R Hicks Jul 2 at 11:16
    
I suspect it is a typo for "ball bearing". –  Reinout van Rees Jul 2 at 19:14
    
Pretty much everything in a bicycle has ball bearings, though. –  Batman Aug 2 at 19:42

If it happens striclty once per revolution, then it is likely to happen exactly at the same pedal position every time. For example, "every time when the left pedal begins the downstroke".

If this is the case, it must be in the front part of the transmission, since any problem happening in the rear, will be multiplied by the gear ratio and so, it will happen at a different pedal position each time, (unless you have a 1:1 ratio).

There are a few things that can be felt like a skip that happen on the front side.

First is a damage in the bearings and cup of the crank axle. If it is a Sealed Bottom Bracket, then it may need replacing. A Cup and Cone type BB, may get away with replacing only one component, but they tend to be cheap and it is better to replace the whole system (Or even upgrade to sealed). By "a damage" I mean a dent in a cup or in the spindle.

There can be something loose. It is known for square tapper cranks that if they are used while not tight enoug, the square hole can get deformed and out of shape, alowing the crank to wiggle. It is usual though that the foot only feel one direction of the wiggle (i.e. you dont feel when it "wiggles back", usually half a revolution after the initial wiggling). Sometimes this type of damage persists even if you tighten the crank retaining bolt. I have little experience with cottered cranks, but I guess similar things happen to them.

In rare cases, a loose or missing chainring bolt can give this feeling, specially when the chain is not perfectly aligned with the affected chainring.

Yet another cause for this feeling can be a damage in the pedal. I have seen pedals where the cage is damaged in such way that in a specific position of the spindle, the cage wiggles up and down, but only in that position and not during the rest of the rotation. If this where the case, imagine what you would get if the pedal suddenly moves down a little bit during the stroke. This type of thing, however, is usually felt with just one foot, not both.

I Agree with another answer here that you should disengage the chain from the chainrings and try to pedal (while leaned into a wall or a pole, etc.) to see if you still feel the weird thing. By dropping the chain tou isolate the rest of the transmission, and if the problem can still be felt, the it has to be in the front end.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.