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Chain Replacement

You should replace your chain every year or 1000 miles. If you ride hard, or ride in mud and dust, you may need to replace it more frequently. If you've broken your chain, there may be some warp you can't see, and the chain will eat away at the teeth of your rings. Plan to replace a repaired chain as soon as possible.

You probably need to cut the new chain down to size. It should contain the same number of links as your original chain. If you use the chain straight out of the box, it will usually be 3 or 4 inches too long, and the idler pulley may not hold the chain tight enough while you ride.

Put the new chain alongside your old one on the floor. You may notice that the links at the far end don't line up exactly -- because your old chain is worn and has stretched. Match the chains so your new chain has as many links as the old one. Before "breaking the chain" to the length you need, consider how the ends must fit together. If you're using a Quick Link, you need two inner links facing each other, because the Quick Link replaces the outer link that would normally join them. If you're using a pin, you need an outer link on one end, and an inner link facing it. (You DON'T want two inner links facing other, nor two outer links -- you want an outer link on one end, and an inner link on the other, OK?).

If you're starting from scratch, you'll need to put the chain on the bike to estimate the correct size. In general, the chain is the correct length if (1) the chain runs vertical between the upper pulley and lower pulley of the rear derailleur when shifted into the small chainring and the small cog on the rear, and (2) the chain still has "room to bend" when the derailleur comes forward when in the large chainring and largest rear cog.

(On some bikes with very large rear cogs, it may not be possible to shift into the lowest rear gear -- big cog greater than 32 teeth -- while in the highest front gear -- big chainring. In this case, size the chain to the small chainring - small cog combination as in #1. If the chain is too long, it may skip gears.)

ch-brk01.jpg (18060 bytes)

Using a chain-breaking tool, push the pin out of the bushing. If you'll be using a Quick Link connector or a breakaway pin, you can push the pin all the way out.

If you plan to use the existing pin to join the chain, you'll need to stop while the pin is still within the far-side outer side plate. Check the position of the pin frequently. Stop turning when the pin is just on the edge of the bushing, before it begins to move through the outer side plate. (This is about 6 complete turns of the chain tool.) Now back the chain tool out of the bushing.

ch-brk02.jpg (15502 bytes) If you're going to use the original pin (at the site you shortened the chain), tease the chain apart. Wiggling the chain slightly side-to-side, extract the end of the chain containing the inner side plates, roller, and bushing from the outer side plates. The pin should still have a whisker of shaft visible on the inner side of the outer side plate.

Position of the pin after removal of link.

ch-brk03.jpg (13413 bytes) Now route the new chain. To keep tension at a minimum, lay the chain on the bottom bracket at the front (just off the small chain ring to the inside), and route it over the smallest cog at the rear (move the derailleur over so it matches). Pass the chain on TOP of, then in FRONT of the upper pulley, then straight down to the bottom pulley. The chain passes BEHIND the bottom pulley, then forward UNDER it. (Remember FOUR sides of TWO pulleys.) If you have a chain retaining tool, hook it to the chain to keep the tension off. Otherwise, have someone hold the chain in position for you.
Before joining the chain, double-check the routing. The most common mistake is to assemble the chain so it's dragging over the metal support strut between the top pulley and the idler pulley of the rear derailleur. 

Use a retaining clip, a bent wire, or an assistant to hold the ends of the chain. Otherwise, the pull of the rear derailleur makes it hard to assemble the chain.

ch-brk04.jpg (17207 bytes) Option 1: Joining the chain with an original pin

Align the chain end with the inner side plate link so it fits inside the end containing the pin and outer side plate link. Using the chain tool, push the pin inward until it's evenly spaced within the outer side plates.

Pushing the pin into the joint.

ch-brk05.jpg (11946 bytes) The newly joined link will be slightly stiff. Work the repaired link up and down, and slightly side-to-side until it bends freely.

Working the chain to remove stiffness.

chainlnk.jpg (12632 bytes) Option 2: Quick Link

Some chains come with a special connecting link. This link joins two inner plates together. If your chain came with a connecting PIN rather than a quick-link, you can buy these links separately for chain repair. You need to buy the right size (7-speed and 8-speed bikes use one size chain; 9-speed rear cassettes use a thinner chain).

Slide the pins into place through the larger side of the opening in the opposite plate (see photo). Squeeze the link until the pin ends are protruding from each side. Now pull hard until the link lengthens and the pins lock into place. 

The main advantage of a connecting link is: you don't need a chain tool to assemble the chain, nor to take the chain off. To remove a quick-link from your chain, squeeze inward on the link -- push the side plates towards each other. (This disengages the locking mechanism.) Then while holding that inward squeeze, compress the chain lengthwise so the end of each pin slides back into the larger side of the oblong hole. You can then pull the link out by pulling the two halves of the quick-link away from each other.
Option 3: Breakaway Pin

Some chains come with special connecting pins. These have a tapered guide to help you insert the pin

If you're buying these pins as spares, be sure to get the correct size. If you have a 7-or 8-speed rear cassette, your chain is wider, and you need a slightly wider pin than one for a 9-speed chain.


Position the ends together, and slide the tapered end of the pin into place.

Attach your chain tool so it's pushing on the protruding pin. Be careful not to put sideways stress on the pin -- you don't want to pop the pin off the guide now!

Twist the chain tool's bolt until the guide comes out the far side of the link. You'll feel a slight "pop" as the pin advances through the side plate of the chain.

Position the pin so it appears evenly spaced inside the link.

Grab the protruding guide with pliers and bend sideways. It should break away easily.

If necessary, fine-tune the position of the pin within the chain, so it doesn't protrude from either side.

Lube the chain. (Many chains come with a film of sticky lubricant. Clean this off with degreaser. Then use your favorite stuff.)

Your new chain will be a bit stiffer side-to-side. You may find that your shifting has changed a bit. If so, fine-tune your front or rear derailleurs.