How to Change a Chain


There are a lot of people new to cycling who are not aware that a

bike chain is considered a “consumable”, that is expected to

be replaced periodically.  

They usually find this out when their bike no longer shifts

smoothly, or they experience chain slip while pedaling.  (If this

occurs while standing, it can be very painful as you come crashing

down on the top-tube of the bike).

Often, you can get away with ignoring your chain except for a

little oil now and then, but you will come to regret this.  

When chains wear, there is often no easily visible indication that

they are doing so.  They seem to look just the same as when new,

just a little dirtier.  But chains wear in an odd way:  they


Now chains don’t actually stretch in the normal sense of that

word.  If you measured an old and a new chain, each link of the

old worn chain will be the same length as a link on the new chain, yet

the old chain will be longer.  You could  painstakingly

count the number of links to make sure that there were the same number

of these same sized links.  Yet, the old chain would still be


The secret:  Chains wear out the connecting pins that

hold the links together. The pins get ground down by all the grit your

chain picks up from the road.  

This wear is hard to see because it’s hidden between the two outer

chain side plates. 

The two outer side plates are friction fit to the chain pin, and

wear does not generally occur there.  The two inner plates are

meant to swivel around the chain pin each time the chain goes around

the gear. This repeated motion slowly grind the pin diameter


Slowly, over time, the effective diameter of these pins gets

smaller, and in some sever cases they get groves in them.  In

addition, the holes through the inner set of side plates (or the

bushings in those holes) become slightly oval shaped.

Chain “stretch” then, is simply the accumulation of

a tiny bit of wear over many pins. Normally, a chain link is half

an inch from pin to pin, and one full inch from the start of one link

to the start of the following link
  (Yup, it’s measured in

inches, not centimeters, it’s always been this way).  When the

pins wear, the overall distance between them gets further

This image shows wear on the pin.

 Note the grove indicated by the arrow. This wear was

caused by about 2000 miles of riding in a gritty

climate.  Click image for larger view.

So What?

Who cares if the chain “stretches”?  You do (or you should) and here’s why.  

A worn chain measures just a tad

longer between the pins, and does not mesh well with the gears

on the bike, all of which are carefully made to mesh perfectly

when the pins are half an inch from each other.  As the

pins move further from each other they come to rest on a

different part of the gear tooth.  Instead of nestling

smoothly in the hollow between gear teeth, they land on the

face of the following gear tooth, and start to wear that tooth

down.  The photo at right shows what can happen if you

let it go.  

The black chainring was from a neglected (but often ridden)

bike, and the silver colored ring is new.  Note the ugly

wear pattern, where the leading edge of each tooth is badly

worn down.  This bike had a bad case of chain skip and

poor shifting.

Putting a new chain on worn chain rings will yield worse chain

skip. So neglecting the chain means you not only get to replace

the chain (fairly cheap) but now you also have to replace the

chain rings and probably a few cogs on the rear gear cluster as

well.  This can get expensive, especially if your rear cogs need

to be replaced. It’s much cheaper to replace the chains in a timely manner.

How Often to Replace Chains

The rule of thumb is you should replace your chain BEFORE a foot of

chain has stretched to the point where it is a foot and one eight of

an inch. 

Checking this is Simple:  

  • Shift to the big-big gear combination. (Gives a nice long place

    to measure).

  • Lay your bike on its left side.  

  • Lay a one foot ruler or tape on the top run of chain such that

    the Zero mark is dead center in one of the chain pins.  Hold

    it there very steady.

  • Check the other end of the ruler.  On a new chain it will

    be dead center on another chain pin.

  • If the chain pin center is less than 1/16th beyond the end of

    the ruler it’s OK.

  • Between a 16th and an 8th, you should think about changing the

    chain at the earliest convenience.

  • If the chain pin center is 1/8th of an inch beyond the end of

    the ruler it is past time to change your chain.

You may get anywhere from 2000 miles to 20,000 miles on a bike

chain before it needs replacement.  It all depends on how much

grit and dirt accumulate on the chain and your style of


Tools you will need:

Bike shops have a nifty tool measuring chain “stretch”

but it is no more accurate than a good ruler.  You can have them

double check your measurements when you ride down to buy your new


You can have them install a new chain for you, or you can do it

yourself.  It’s a skill that may be good to know in case you break

a chain miles from anywhere.

You need a Chain Tool.  A Chain Tool

is used to push the pin out of the chain so that you can take

out links to make it the right length.  You need to do

this with each new chain.  Expect to pay under $14 for a

good chain tool. 

There are several models to choose from.  I prefer one small

enough to be carried in my bike bag. 

There are no common household tools that do a satisfactory job of

removing and re-inserting chain pins.  You really do need this


Note that there are some brands of chain that come with a

“easy open” link.  These often require no tools to open

the chain.  When clogged with gritty oil, these can be difficult

to open, and the quickest way may still be the chain tool.  Even

with an easy open link, you need a chain tool to adjust the length of

the new chain.

Other useful (but not essential) items for this task include a pair

of surgical gloves (buy a box at your drugstore), and a small U shaped

piece of stiff wire (coat hanger) that can be used to supply some

slack in the chain by pulling links together so as to make a loose

“belly” in the chain.  Note that the chain tool

pictured on the left (above) comes with such a piece of wire. 

They are easily made however.

Take the Old Chain Off

Taking the old chain off of the bike is the first task that

requires a chain tool.  

Before you get started make a mental note of how the chain runs

thru the Derailer if this is the first time you’ve changes a

chain.  You need to get it back that way when installing the new


Here’s how to use the chain tool.  Position the chain

across the slotted jaws of the chain tool such that one of the chain

pins aligns with the slot.  Then screw the pin extractor till the

mandrel comes in contact with the chain pin.  Make sure

everything is aligned perfectly, and then start turning the handle

pushing the pin out.

Don’t push the pin all the way out. 

If you do, it’s very tricky to get it back in. Always stop when the

pin is hanging out of the side plate opposite the mandrel.  How

do you know when to stop?  Well go slow, and remember the pin

is as wide as the chain, so almost that width will be hanging out

when it’s far enough.  Also, there will be a slight increase in

resistance when you are “far enough”.  This

resistance is caused by the ends of the pin being ever so slightly fatter than the

middle, and this fat part has to squeeze thru the side plate.

Periodically stop before you push the pin all the

way out and see if you can pull the chain apart yet.  (It’s ok

if the pin extends a bit on the inside of the plate, because

slightly bending the chain from side to side will overcome

this).  Removing the OLD chain from the bike is the proper

time to experiment with this, not on the NEW chain.
After a

couple tries it becomes second nature.

As you finally break the chain, if this is the first

time you changed a chain WATCH the Derailer. It will swing

back.  Carefully note how the chain was routed through it. It

looks different in this swung back mode.  You have to route it

the same upon re-assembly. 

Hang it Up 

Ok, now you have that old filthy chain off.  Don’t toss it

just yet.  We will use that chain to adjust the size of the new

chain.  (Chains always seem to come a few links longer than you

need).  You can count the links in the old and again in the new

chain, and then use your chain tool to remove the excess


But my quick way is to take old and

new chain and hang them on a horizontal (headless) nail that I

pounded into the garage for this very purpose. Hang them from

the end of the chain that does not have the chain pin


In the picture at right, the old chain is against the wall

and the clean new chain is nearest the camera.  Note that

the links of the chain all line up at the top of the chain.

But because of chain “stretch” you will see that

the don’t line up when you get farther down the chain.

In severe cases this will cause you to miss-count the

number of links and your new chain will be one link too long

when you install it.

Here you can see that near the

bottom of the chain, the links are off, with the old chain

pins hanging half way down the link of the new


To get the correct number or links, you need to go down the

chain with your fingers lifting the old chain when ever

it drifts out of alignment with the new chain.  Lift it

till its pins line up. Then move down a bit further, and lift

again.  You can quickly do this lift and align trick,

(about three times I’ve found) till you arrive at the bottom.

Grab link of the new chain that corresponds with the bottom

link of the old chain.

Note which pin you have to push this link by comparison to

the old chain.  It will be the bottom most pin as the

chain hangs on the nail.

Now, reach for your trusty chain tool and push that pin ALMOST

out.  Here is where you will really kick yourself if you push

it too far.  In fact if you do, it’s easier to punch the next

pin up (on the big piece of chain) all the way out, discard the two

side plates that will thusly be freed,  then flip over

the small piece of chain and re-join it to the big piece, and then

CAREFULLY push the pin at the opposite end of this same link almost

(but not quite) out.  Take my word for it, this is easier than

trying to convince a loose pin to go back into the side plate.

You should end up with something like this.

Note Pin could have been pushed a tad

further, but this was enough to bet the chain apart.

The pin should be sticking out of the LONG piece of chain and the

short piece can be discarded.  If the pin is sticking out

of the short piece of chain, you pushed the wrong pin out, and you

will have to re-join the chain (see below) and push the other pin


Put the New Chain On

Now it’s time to put the chain back on the bike.

After adjusting the size of the chain, you have to put it back on

the bike.  Since the chain passes through the frame’s rear

triangle, you can’t just assemble the chain and then put it on the


I find it’s easiest to do this with the bike laying on its left


Note: if your Derailer pulleys are excessively worn now

is an excellent time to replace them.  Get a new set from

your local bike store (you need to tell them the name and model

number of your Derailer).  You may need an Allen wrench to

unscrew the bolts that hold them in.

It’s easiest to do this is string the (as yet un-joined) ends thru

both detailers, in roughly the normal path of the chain.  But

first run the front Derailer all the way in (over the smallest chain

ring) and shift the rear Derailer over the smallest cluster gear.

This way, you will have the maximum slack to work with instead of

having to fight the spring tension of the rear Derailer.

String the chain through the front Derailer from the rear, and to

the side of the smallest chain ring (missing both chainrings altogether,

just lay it on the bottom bracket next to the chainrings).  Let

enough hang down to get half way to the rear Derailer.

String the other end of the chain over the rear

side of  the smallest cog, in FRONT of the upper Derailer

pulley, (remember you have to pull the Derailer arm (some

times called a Derailer cage) down to its normal position

against its spring).  Then down to and BEHIND the lower

pulley and toward the other end of the chain. (See red-line at


Watch out for metal tabs on some models of Derailer

arm.  Don’t loop over these tabs, go behind them, between

the left and right arm-members.

 Now you are ready to join the two chain ends

together.  Carefully push the narrow end of the chain between

the side plates of the other end.  Align it so that the pin is

in line with the hole in the link.

Use your chain tool to drive the

pin back in
, as shown here.  If you are careful when

stringing the chain back on the bike, the pin will be pointing

away from the bike, making it somewhat easier to use the chain

tool.  It’s no big deal, though, and you can have the pin

pointing either way by simply turning the chain over before

you string it.

Push the pin in till it is flush with the other side, and

no further.  Remove the chain tool.

You will find the chain is stiff at this link.  That’s

because the side plates are pushed tightly together by the

chain tool.  Flex the chain by bending it with your


Bend it up and down (they way it was designed to

bend) and also left and right, (the way it wasn’t meant to

bend).  This will free up the side plates so that the chain

will flex a bit easier.  Sometimes a small regular screw

driver blade can be inserted between the outer side plates and

twisted just slightly to push the plates apart giving smooth chain


Now put your chain on the front chainring, and crank

it around a few times slowly.  Watch for kinks going thru the

rear Derailer.  If the Derailer jumps or twitches, it’s a sign

that the link you joined is still stiff.

Oil your New Chain.  

The grease covering your new chain is primarily a

rust inhibitor, and does not provide proper lubrication.  Oil

it with 1 drop of oil at each of the pins (applied to the top of the

chain).  Then wipe off any excess. 

No Derailer?

If your bike is a single speed, or has a geared rear hub, the

procedure for replacing your chain is different only in a small


You might be able to get the old chain off without loosening the

rear wheel because of the chain “stretch”, but you will have problems getting the new chain on because it may be too tight

to get the final pin in.  If so, loosen the bolts that hold the

rear wheel, and slide it forward or dismount the wheel


When replacing the wheel don’t pull the chain so tight that there

is no play in it.  You should be able to pull the bottom run of

chain down about half an inch to a full inch.  If not, it’s too

tight, and will wear your gear unnecessarily. 

No Old Chain?

Sometimes you have to put a chain on a bike and you don’t have

the old one to use to get the new chain length correct. 

This can happen when you are building a new bike from parts, or

you break a chain while out riding and neglect to bring the pieces


In this case, wrap the chain around the largest front chainring,

and over the largest rear cog, and thru the Derailer. Then pull the

ends together on the bottom run of chain, over lapping them, until

the rear Derailer arm is pointing as far forward as it will

go.  Be sure to pull these two chain ends in-line, not down, or

to the side, but follow the natural path the chain will take.

Mark the link that lines up with the end of the chain when the Derailer

arm is fully forward.  You need a little excess length in the

chain to facilitate shifting, so add two links minimum, maybe three

if your Derailer spring is really stiff.

It’s A Snap

Changing a chain is a snap with the chain tool (and almost

impossible without one).  It pays to be able to do this work

yourself, and it’s not difficult.  The chainrings and cogs you

save by changing your chain are way more expensive to replace.

So grab your ruler and run over to your bike and measure your

chain.  If it’s too long, instead of paying the bike shop to do

this (every time), pay them for a chain tool (once) and do it your

self.  It’s a 10 minute job, and a skill worth knowing.

Source Article

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