Bicycle chain kept jumping out of the sprocket

14 Jan 2010


Bicycle chain kept jumping out of the rear gear sprocket, making plenty of noises and causing jerky pedals when riding. This article will suggest a fix for such problem.

What Can Go Wrong?

Misalignment between the gear sprockets and the chain. May be caused by :

a) poor Rear Derailleur Adjustment
b) Faulty components such as
1) A faulty chain;
2) A bent sprocket at the pedal;
3) A bent or faulty gear sprocket at the wheel;

Adjustment to Rear Derailleur

Many websites have step by step procedures or helpful hints on how to adjust the rear derailleur. The adjustment involves 2 stop or limit screws; one to prevent the chain going beyond the smallest gear sprocket and the other, beyond the biggest gear sprocket when there is gear shift. The following video gives a good understanding on how derailleur works and how to adjust it.

In words

Place the bicycle upside down as shown

1. Put the shifter in high gear and turn the wheel. Tighten the high gear screw in one direction until one can no longer shift beyond the smallest gear sprockets into high gear then backup the screw in the other direction until a larger gear is engaged. After that, turn the screw a little more until the derailleur shifts smoothly onto the smallest gear sprocket.
2. Put the shifter in low gear. Tighten the low gear screw until one can no longer shift beyond the largest gear sprockets and repeat the same as the high gear screw.

What if the Derailleur Adjustment Does not Work?

Check the condition of the gear sprockets at the pedal and the back wheel. If the bicycle is in good condition, the gear sprockets should run truly vertical without any wobbling when the pedal and the wheel are running. If the gear sprocket wobbles, it could suggest that either the sprockets are damaged or the pedal/wheel shaft is bent. It is time to dismantle the back wheel and examine the sprocket or shaft for damages.

Why Shaft bends?

The pedal shaft seldom bends because they are usually of larger diameter; however, when the chain jumps out of the rear gear sprocket, the chain could be caught between the gear sprocket and the bicycle frame. Any subsequent heavy forces applying onto the pedal could bend the shaft.

Actions to be Taken

If one is lucky and the sprockets is not damaged, it will just be a matter of replacing the shaft or having the shaft straightened. Replacement of the shaft is recommended because bent shaft will require special tool to straighten. A little bit of wobbling usually won't cause gear jumping.


衣服顏色 said...

真正的友誼,有如健康失去時,始知其價值 ..................................................

停止 said...

回應是我能為您做的最大的支持 ........................................