Dropped chain? Does the chain fall off again?

In the bike transmission system, the chain is the fastest wearing among the crankset, chain, and flywheel. Daily maintenance and repair are essential for riders. In this article, let’s talk about the chain. 

1. Structure

The chain we commonly use is mainly composed of an inner film, an outer film, a pin, and a Roller, and is generally connected by the pin or quick link at the end of the chain. Figure 1 shows how they connect.

Chain structure

2. Disassembly

(1) Adjust the front and rear gear shift to the smallest ring. At this position, the pulling force which the derailleur acts on the chain is minimized. 

(2) Select the chain breaker according to the derailleur speed. Put the chain into the clip and gently press the roller with your hand, rotate the handle and align the tip of the thimble with the center of the pin. 

(3) Turn the handle to push the pin out of the outside film. Stop turning when you feel the resistance suddenly decrease and then withdraw the thimble, and remove the chain. When removing the chain, pay attention to the direction, it’s better from the front derailleur to the rear. Be careful to hold the chain firmly to prevent the chain from scratching the frame. If there is no pin roller or quick link with you, do not press out the pin completely so that it can be easily pushed back during installation.

Disassembly chain
Quick link and pin

3. Installation

(1) Determine the appropriate length of the chain. If needed, cut off the chain.

Chain cutting position

(2) Figure 5 shows the cutoff position. 

(3) Adjust the front and rear gear shift to the smallest ring. 

(4) Hang the chain on the smallest chainset through the front derailleur, then go around the top of the flywheel and hang on the smallest gear. When installing the chain under the rear fork, the end of the chain on the left side is the inner film, in contrast, the right side is the outside film. 

(5) Make the chain pass along the rear derailleur guide wheel from the inside of the baffle, bypass the tension wheel, and use the chain puller and breaker to push the pin until you feels lighter, that means the pin is in place

Chain adjustment

If a quick link is used, it must be tightened when connecting; if there is no quick link or new pin, use the opposite steps which remove the chain to install it. Note that ‘returning the chain to its original place’ can only be used as a temporary emergency measure. The pin is small and the fitting force is insufficient after being reinstalled, the chain will easily break again. 

4. Maintenance

(1) Clean

When cleaning the chain, wipe it with a cloth dipped in a little neutral detergent. Do not soak the chain in detergents, corrosive solvents, or organic solvents such as gasoline or diesel. Otherwise, the grease can easily be removed which leads to corrosion of the chain. 

(2) Lubrication

Use the special oil to lubricate the chain. The main oiling part is the pin. You can brush the oil to the roller below the chainstay and rotate the crank counterclockwise to apply the oil evenly on the chain surface. 

(3) Replacement

Replace the chain when worn too much or stretched over 0.8mm.

Chain length measurement


[1] ‘Cycling Bible’ Editorial Board. Cycling Bible [M]. 1st Edition. Beijing: Machinery Industry Press, 2013.

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