Once your mountain bike chain becomes damaged, you

should immediately replace it with a new one.  It

is possible however, to repair a broken chain using

a chain tool.  For this very reason, most mountain

bikers travel with a chain tool.

 

Your chain has three basic components - the metal

side plates, the rollers between the side plates,

and the rivets, or pins which go through the rollers

and help to hold the plates together.  These pins

allow the rollers to freely turn as the chain

moves around the cogs.

 

If your chain happens to break, you'll need to remove

the broken link and replace it with a spare link.

To do this, simply reattach the two ends of the

broken chain and ride on a shorter chain until you

can get it replaced. 

 

To remove a broken link of chain, place it in the

chain tool.  Now, turn the tool counter clockwise

until the rivet pin of the chain tool touches

the chain rivet.  Continue to turn the tool until

the pin pushes out of the roller.  Be very careful,

as you want to stop turning when the pin is right

at the edge of the roller, before it moves through

the outer side plate.

 

Now, turn the tool in the other direction, and back

it out of the roller.  Set the tool to the side,

then work the chain very gently from side to side

and extract the inner side plates and roller.

 

Now is the time to re-route the chain through the

bike.  You may want to have a chain retaining tool

or some to help you hold the chain in the right

spot as you route and repair it. 

 

Now that the broken link has been removed and

you've re-routed the chain, you're ready to insert

a new link or simply connect the links that were

beside the broken one.  The process here is the

same - align the two ends so that the link with

the inner side plates will fit inside the link

with the pin and outer side plates.  Now, use the

chain tool to push the pin inward until it's

positioned evenly between the side plates.

 

The easiest way to learn how to do this or feel

comfortable doing it is to have someone show you,

then actually practice with a chain and a chain

tool.  You'll have no trouble at all making a

temporary repair in a mountain bike chain once

you've seen it done by a professional and practiced

it yourself a few times.