"Is rust the reason my bicycle chain came off? What else could it be?" "Can I fix the chain myself?"

Today, we'll answer those questions.

In conclusion, it is possible to fix a bicycle chain yourself.

However, the repair method varies greatly depending on the type of bicycle, so it's still best to have a bike shop take a look.

That said, we will explain how to fix it yourself for those who might encounter a detached chain again in the future and want to minimize costs.

By referring to this article, you can fix your chain yourself without spending money.

Reasons why a bicycle chain comes off

First, let's look at the reasons why a bicycle chain comes off.

Consider if you can fix it yourself after learning the causes.


Reason 1: Aging and deterioration

One reason a bicycle chain comes off is chain deterioration. It is said that chains have a lifespan of about 3,000 to 4,000 kilometers, and when they reach the end of their life, the connecting parts wear down and become loose, causing the chain to come off.

Therefore, if the chain comes off due to aging and deterioration, the chain itself needs to be replaced.

If you're not sure if it's loose, the quickest way to find out is to have a bike shop check it.


Reason 2: Dirty chain

If your bicycle chain is covered in rust and dirt, it can also come off.

For example, when a chain rusts, the derailleur and chain stick together, losing their original tension and causing the chain to come off.


In this case, to keep costs down, it's best to remove the rust.

However, at this point, the rust is likely quite severe, so it might be better to replace both the chain and the derailleur.


Reason 3: Derailleur malfunction

A bicycle chain can come off due to a loose derailleur adjustment, or deterioration or malfunction of the derailleur.


If the chain comes off due to a derailleur malfunction, you can adjust the derailleur yourself, but if it's due to deterioration or a fault, have a bike shop check it.


Reason 4: Chain tensioner

If you ride a bicycle with an internal gear hub, such as a "mamachari" (city bike), the chain tensioner is the cause. This refers to a state where the part that adjusts the chain tension is loose.

Adjusting it yourself is difficult and challenging, so most people would have a bike shop look at it. However, if the chain comes off due to a chain tensioner issue, taking it in for repair can be quite expensive, so we recommend adjusting it yourself.

How to fix a bicycle chain

Now, let's thoroughly explain how to fix a chain.

It's easier than you might think, so give it a try.

How to fix a bicycle chain that has come off the front gear:

・Place the chain on the gear according to the derailleur number
・Slowly rotate the pedal backward

You can fix it if the chain isn't too loose.


How to fix a bicycle chain that has come off the rear gear:

【Derailleur adjustment】
・If the chain has come off to the outside: Set the derailleur to the "smallest number"
・If the chain has come off to the inside: Set the derailleur to the "largest number"

【Gear adjustment】
・If the chain has come off to the outside: Put the chain on the small gear
・If the chain has come off to the inside: Put the chain on the large gear

【After derailleur and gear adjustment】
・Slowly rotate the pedal forward


Similarly, this can be fixed if the chain isn't too loose.

Note that forcing a rear chain back on can cause it to jam awkwardly, so adjust it slowly.


Additional note: Rust removal basics

Rust removal only cleans the surface, so even if you remove rust, it will quickly reappear.

Therefore, if there is rust, it is recommended to replace the chain itself.

Also, after maintenance, oil is applied to prevent rust and ensure smooth chain movement. However, highly viscous oils tend to attract dirt and sand, while low-viscosity oils can easily spray off or wash away in the rain. Therefore, regular maintenance is essential.

For detailed information on maintenance, please refer to "Bicycle Maintenance Methods."



It's difficult to fix a mamachari chain yourself

If the rear chain of a mamachari (city bike) comes off, honestly, it's difficult to fix yourself. This is because bicycles without derailleurs have a uniform chain length, so it's rare for the chain to come off unless there's a significant issue.

Therefore, about 80% of the time, the cause of a detached chain is chain looseness.


Most people would probably take it in for repair, but the labor cost for bicycles with chain covers is very high, so it's better to repair it yourself if possible.

Non-derailleur chains can be bought online for a few hundred yen.



Repair cost at a bike shop for chain issues