How To Use A Chain Tool

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.