How to Fix a Bike Chain





Introduction: How to Fix a Bike Chain

About: Dan Goldwater is a co-founder of Instructables. Currently he operates MonkeyLectric where he develops revolutionary bike lighting products.

Fixing a bike chain on the street is no harder than fixing a flat tire if you are prepared.  Read on...

This article is sponsored by Momentum Magazine and MonkeyLectric.  An edited version of the article appears in Momentum issue 50

Step 1: What You Need

To fix a broken chain all you need is a chain tool. These are compact and built into many common multi-tools like the one shown. You may even have one on your multi-tool that you never even knew what it was for!

At home in your garage its possible to repair a chain with just a hammer and pliers, but a chain tool is easier, and really the only option on the street.

Step 2: How Do Chains Break?

The most common way is by pedaling full force at the same moment that you are shifting your front derailleur. Other breaks I've seen were caused by an assortment of seemingly one-in-a-million occurrences, yet i've seen enough of those cases that i guess if you ride long enough one-in-a-million still happens. Things like a nail getting thrown up by my front wheel and lodging in the chain, then getting cranked across the sprocket. who'd a thunk?

Step 3: How Do Chains Work?

Each link of a chain is held together by a steel pin / peg. With the chain tool (or a hammer) you can push out and push in the pins, allowing you to remove or attach links. Fixing a broken chain amounts to removing the broken link and re-attaching the remaining ends. On bikes with derailleurs there's enough extra links that you can remove a couple without a problem. On a single-speed bike you probably won't have enough slack in the chain to remove a link, you'll need to borrow some links from an old chain or else buy a new one.

Step 4: Your Chain Just Broke, Now What?

Are you wearing nice clothes that you care about? Probably best to lock your bike and take the bus home. Come back later with your old jeans and we'll fix it then. Fixing a chain is the dirtiest job there is on a bike.

Step 5: Take a Look at the Chain

Ok you're back and ready to go. Flip your bike over so you can get to the chain more easily.

Take a look at the two broken ends. One end (possibly both) is damaged and needs to be removed.  What you will do is to remove 2 segments of the chain at the damaged end.  You need to remove 2 segments instead of 1 because the two types of segment alternate. If you just remove 1 segment you can't re-attach it. 

Place the chain into the groove in the chain tool (see photo) at the spot you want to disconnect. If you are replacing a worn but non-broken chain you'll do the same thing here.

Step 6: Separate the Chain

Turn the screw on the chain tool to start pushing the pin out of the chain (see photo). be careful to keep the pin on the chain tool lined up with the pin on the chain, sometimes they like to slip around a bit.

Don't push the pin all the way out! Only push it just far enough so the chain comes apart (see photo). You need to leave the last bit of the pin in the chain so you can push it back in later.

If you want to do this without a chain tool:  drill a hole in a piece of wood and place the pin you want to remove over the hole.  find a machine screw about the size of the chain pin and use it as a peg to bang the chain pin out with a hammer.  It's tricky because you don't want to bang it out all the way.

Step 7: Re-attach the Links

OK, now feed the chain back onto your sprockets. It helps a lot if you have a friend who can hold the two ends in position while you reattach them.

Use the chain tool to push the pin back in (see photo). This is the trickiest part to keep the tool lined up with the pin. Note: if you are putting on a new chain here, many new chains come with a special link that makes the first-time installation possible without pushing any pins in.

Step 8: Work It Loose

Once the pin is in, the link you just attached will be stiff. Work it back and forth (see photo) until it loosens enough to bend around the gears.

Take a look at your hands and feel proud. You have done something real today.

Step 9: Reuse

If you were just putting on a new chain in the comfort of your home, now got an old worn chain to reuse! Since you know how to remove links and reattach the segments, you can use part of the old chain as a cable to lock your seat onto your bike. This is very handy in urban areas.

You can also make yourself a bike chain bracelet or an earring. You'll need a fairly big piercing and a tough ear to get that stud through.



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18 Discussions

I have one exactly like that!

i need 7mm by 3.6 mm chain pin and cant find it on e bay or enywhere else. it looks pretty much the same like the one on the pic above. can someone please recommend someone who can sell me what i need. ty

Hi, thank you for the instructions. I made a previous repair in my bicycle and i thougt i was wrong. Reading this solved my questions.

Is that a mood ring! I have one exactly like that!

Where can I buy a chain tool in stores.

got me thinking... from what i understand a chain tool is basically just a watch link tool but bigger... im not sure but it might be doable

Great instructable.

We now have a chain on the bike that has a nifty no-tool-link but we can't get it off.
It looks like an open chain link, flat on each side and is supposed to come off by hand...

Does anybody know what the trick is?

4 replies

Here is a sketch I just made of common type of tool-less link, with some tips for getting it apart. Reverse steps to join chain.
By the way, modern chains for derailleur systems come in different widths, 8 speed, 9 speed, 10 speed, etc. If you buy a superlink for your chain you need to get the proper width to match your drive train. (Count the rear sprockets.)


This is the one! Thank you!
(I replied to the other sketch before seeing this one)
I will tell you how it went :).

Glad to help. Note that a tool-less link that has been on for many miles, or is on a dirty or gritty chain, can bind the super link a bit with grit in the keyholes, etc. In that case you may have to gently use needle nose pliers to help move the mating plates for removal. There is a special plier-like tool that pro mechanics have on their benches to help with that. But at my home bench I just use needlenose pliers. Avoid making burrs or munched metal edges on the superlink; file or sand them if that happens.
A superlink is not a "forever" part, btw. If you keep using the same one on a succession of replaced chains, it could eventually break. Much as an ordinary chain that is overmileage can break, or a chain that has had an OEM pin pounded in and out, will fail.
I have broken one myself, one of the pins failed by breaking off of the plate. But it was a used one of unknown mileage and I should have known better. Not a problem, though: along with a patch kit, pump, and spare tube, I always carry a small chain tool, a couple of hyperglide pins, and if I have one, a new superlink as well. A few spare ordinary chain links complete the set in case of a chain that gets hopelessly bent or something.
Keep in mind that if you elect to work on your own chain, having a tool-less link won't obviate the need for a chain tool entirely. To join up a new chain straight out of the package, even one that has a tool-less link in the package, you will almost certainly have to have a chain tool on hand so you can remove a few links to make the chain fit your drivetrain. If old chain length worked fine, lay new one flat on bench next to it, and copy the length. Use tool to get rid of extra links, then put chain on bike and join it with the handy superlink.

In my opinion, a tool-less link's highest and best use isn't to free us from having to buy a chain tool--for a well-rounded bike mechanic will still need one as seen above. And any rider not wanting to get stranded should carry one, even if they have a tool-less link on the bike. What if you bend the chain a few links away from the superlink? The best part is that you can remove and replace a chain without stressing it, for cleaning. (I do intermediate cleaning on my own bikes, on-the-bike: a rag with citrus solvent, grab the lower section, pedal backwards, thoroughly 'pedal' chain through this rag. Oil, wipe down again so as not to have an oily "dirt magnet." Only at longer intervals do I remove chain for cleaining/soaking.)

There are some other principles to drivetrain maintenance, replacement, etc. , I think I will have to gather up all of these comments I've made, add to them, and produce an instructable.

If this is the type most commonly seen nowadays, you need to:
-Get some slack in the area of chain where link is. (pull chain off of the chainrings, let it flop onto the crank bearing part of frame.
-the special link won't come undone if it is in line with the rest of the chain:
You need to have the adjoining lengths of chain that connect to this link, held at ninety degrees to the superlink. Once you manage that, squeeze the back plate of special link down, while at the same time pushing the front plate of special link up.
-if done right, you end up with two separate pieces that make up the special link. Each one has a single pin at one end of it's figure-eight shape, and an oval keyhole at the other end. By mating these two pieces the connection is made.

-just remember you can't undo the connection if the chain is strung out all in a line. You have to make those 90 degree bends. Otherwise the chain plates do not have the necessary leeway to free the interlocking pins from the special keyholes.

Hi Dan, aka Monkeylectric, your guide will get riders home, it's true. I love how it feels to be able to handle any mechanical emergency using wits and improvisation. I refer to it as "Swiss Family Robinson" style: folks like us stuck on an island would be able to come up with novel remedies with whatever is at hand, right? I remember once my nephew broke a chain some miles from home. I found a large rock as an anvil, and a small rock for a hammer, and we bashed the pin at the separated link back together enough to resume riding, though he kept his pedal pressure light. We'd both forgotten to carry our chain tools that day. Thankfully the pin was still attached.

But seriously, in the case of repairs as well as for initial assembly purposes, you shouldn't be working with the short OEM pins ever. If there is one dangling on there from the factory, you should "lose it." (it may have been left on at the factory for expediency.) As you've seen, in the box nowadays there is either a bullet leader type joining pin, twice as long as the OEM pins; you will be snapping off the forward leader portion after driving the pin home, or better yet, the box will contain a keyhole-type quicklink that is tool-less and can be undone indefinitely without stressing the chain. I just partly covered this in a reply I was giving over at my bike car instructable today. (30 yr. pro bike mechanic here.)

Most all modern chains-this has been true for more than 10 years now-- require the use of a special bullet-shaped leader pin to keep from gouging out the holes in the hardened side plates, if you are not going to use the quick link type fastener. (quick links, such as by SRAM or KMC etc. make a nice upgrade to your chain if you didn't get one initially, btw) These pins are consumable items, known as "hyperglide pins" in Shimano-speak. I carry a few with me in my seat bag along with the chain tool.

Some folks don't know you can't drive existing chain pins in and out willy-nilly anymore. The hardened side plates-this hardness is a key point- will shed fingernail-shaped crescents of metal if you re-drive an OEM pin, (instead of receiving the pin in the more malleable way that chain plates used to do) and so enlarging the holes and immediately weakening that link of chain. Put a white towel down on your bench, drive a regular pin in or out, and look for these tiny metal shards. In a shop environment we witnessed many chain failures right after a customer skipped using the proper joining technique for these hardened side plates. In the beginning the change in technology was more published to mechanics but most good shops will give chain buyers a brief lesson about this now.

The increased side-loading of modern shift patterns requires that chains be hardened, with robust pin-into-plate design, and tight pin tolerances. It's a real improvement, though: the engineering of "hyperglide" and similar drivetrains has allowed us riders to shift under load, especially on the rear. The twisted-and-ramped sprocket machining, along with these hardened chains that can bend locally without breaking, lets the chain grab onto an adjoining sprocket's tooth--at the very same time as we are still driving hard on the cog we are exiting. It's fantastic for keeping momentum while shifting. You'll remember in the 'old days' it was not only good form, but at that time downright necessary, to ease up on the pedals if we wanted the darn chain to nicely grab a better sprocket for that hill we were tackling.

Somethin' else, on loosening a tight link: lacking the right tool, bending the chain back and forth might loosen a tight link, but the pro tip is that the second fence on better chain tools (sometimes compact seat-bag chain tools don't have the 2nd fence) is used to nudge the far sideplate away just a touch. This is what takes the bind out. You'll notice that when using the primary fence of a chain tool, at the extreme end of tool away from the threaded drive rod handle, this fence butts tight up to the far sideplate. All your driving force is met by this primary fence. When you park the chain on the nearer secondary fence, you can see a space behind the far sideplate: this lets that plate migrate a touch away from the center rollers = nice free link. Shouldn't be overdone, it's a very subtle tweak of the drive rod. If the near end of the chain pin submerges below the hole of the near sideplate, you've overdone it; aim for just a bit proud. You should be able to catch your fingernail on the head of the driven joining pin when done right. Also, don't try to do a full-on drive-out-the-pin on that 2nd fence; darn thing will break on you at some point as it's only meant for that 'light touch operation' I outlined.

Anyway, just so you know I love seeing any and everything about bikes at this site-not trying to pull rank on you. I know you'd share your expertise with me as well. Cool stuff. Great place to learn.

2 replies

Here is a sketch I made of a hyperglide pin. You should not use a hammer and anvil to drive it. Use a good chain rivet tool, that ideally has two fences. (inner fence is for adjusting any binding/tightness out of the link.)


Thank you for your reply. I solved my problem for the time being. I will take a picture of the links I was talking about and show it here. (It was bought in Holland)

the bracelet looks amazing , i think i'm going to make one this summer :) , thanks for the idea

Well there you go, that is what I was missing as a kid a Chain Tool! I didn't even know they exist!

This is great, I've got to get one of those tools. At one point I had to repair a chain in the middle of nowhere and ended up using a crap load of lock wire. Never did break and it held for the 40km I needed to do.