How to Replace a Bike Chain
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  Posted November 20th, 2013 by Zdenko  in Cycling, TOOLBOX | No comments yet.

Cycling Toolbox

Source: Bicycling life

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 “stretch”. 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 numbers of these same sized links. Yet, the old chain would still be longer.

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 grinds the pin diameter down. Slowly, over time, the effective diameters 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.

DSC_3530Simple check for chain stretch

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.

WornRingsThis photo 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 pedaling.

DSC_3521New chain: Shimano CN-7901 for 10 gears

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 chain.

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. 

park-ct-5-chain-toolChain 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 tool. 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 one.

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 links.

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 protruding.

DSC_3522In this picture the old 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 they 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 chain. 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.

DSC_3520You 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 out.

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 bike.

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 derailleurs  in roughly the normal path of the chain. But first run the front Derailleur all the way in (over the smallest chain ring) and shift the rear Derailleur 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 Derailleur. String the chain through the front Derailleur 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 Derailleur.

String the other end of the chain over the rear side of the smallest cog, in FRONT of the upper Derailleur pulley, (remember you have to pull the Derailleur arm (some times called a Derailleur 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 on the picture).


Watch out for metal tabs on some models of Derailleur 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 hands.

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 movement. Now put your chain on the front chainring, and crank it around a few times slowly. Watch for kinks going thru the rear Derailleur. If the Derailleur 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 way. 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 entirely.

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. 

DSC_3518New chain successfully mounted

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 home.

In this case, wrap the chain around the largest front chainring, and over the largest rear cog, and thru the Derailleur  Then pull the ends together on the bottom run of chain, over lapping them, until the rear Derailleur 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 line up with the end of the chain when the Derailleur 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 Derailleur 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.

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Source: Bicycling Life


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