If you ride a bike, it's pretty much a must to know how to fix your bike's chain, because it will inevitably fail at some point; more times than not at the furthest distance from where you need to be!
Fixing a chain usually requires removing the damaged links and putting it back into working order by installing a "quick" link or link-pin, which creates the seamless chain loop.
In order to fix the chain, you'll likely need a tool called a "chain-breaker," don't worry, it's also a chain fixer! (Park Chain Tool: right)
When a chain breaks in two, it usually will look a little like the photo to the upper left corner.
To keep this article from getting too complicated, a basic understanding of what makes up a chain is this; a chain has four basic parts, inner-links which are 2 plates that as spaced apart with rollers, and outer-links that hold together inner-links by sandwiching them between 2 plates that are held together with pressed-in pins. 1 set of inner and outer links mated by pin = 1 full link.
When a chain breaks, like in the above photo, the outer plates usually cracks or gives way where the pin is pressed in; which allows the outer plates to peel apart / chain to split.
Depending on whether you are using a Quick-link or a link-pin for the chain repair, makes a difference about what steps you need to take next. Either way, you will need to do is remove the broken sections of the chain using a chain-tool (below right pic) by "de-pinning" the broken sections until they fall apart, leaving only the desired chain.
Take a look at the photo on the left, you'll see 3 items, in the middle and left, are a pair of half-links (outer plates and two pre-installed pins), also known as a Quick-link, the item on the right is a link / press-pin.
Link/Press-Pin Installation: To install the traditional press-pin, you'll need to get the chain to a point where you have a pair of good outer-plates and a pair of good inner-plates that can be mated by inserting a press-pin.
Quick-Link Installation: Unlike the link-pin fix, the idea behind the a Quick-Link is simple. Remove the broken outer-plates to the point that you have a pair of inner-links at end of the chain; once at this point, install quick link by slipping each half-link (pin side in) through the open holes in the inner-links until each half-link pin groove meets the other. Now grab the chain on each side of the fix point and pulled length wise; you should hear a "snap" as the plates and pins lock together. (Photo right: quick-link in locked position)
People will argue to the end of time which system in better, and I myself have used both and see the potential in each system, but we can save that discussion for it's own post in the future.
Side Notes: No matter which "fix" you decide on, make sure that you are using the correct size for your application! Chains differ in size and based on number of gears and brand. So you must make sure that your "fix" is for SRAM, Shimano, Campy, Single-speed, 7,8,9,10 or even 11 speed compatible and everything in between!
Installation Notes Expanded:
Quick-Link Installation NOTES: Quick-links have oval looking holes which are really two holes side-by-side, the inner most hole is what the pin head initially fits through by aligning both sets of inner plates, one side of the power link from the back side of the chain, one side of the power link through the front side of the chain, bring together and connect the pins and plates on the inner most hole making sure the front and backside pins are through the plates. Now just pull the chain backwards to slide and set the pins in the holes furthest out. You should feel a "click."
