To shorten a bicycle chain the easy way, you need a chain rivet tool. Although you can improvise the removal of the rivet with a hammer and punch if you're mechanically inclined and have a gentle touch, a purpose-built tool works best and is well worth carrying in your equipment bag for bicycle touring or long training runs.
'Breaking' the Chain
Examine the chain for a quick-removal link, with its larger link hole. If it has one, press the link horizontally against its neighbor to unlock it and pull out the removable pins to create a break in the chain. If not, apply the chain rivet tool to a link along the bottom arc of the chain. Cradle the rollers in the tool and align the tool’s pin with the rivet. Turn the handle to push the rivet completely through the nearer outer plate and partly through the far side of the second outer plate. Only push the rivet far enough to free the inner plates; leave the rivet projecting from the outer plate so you can easily push it back into place, in the next phase. Let the now-unlinked chain dangle from the front chain ring and rear cassette.
Removing Excess Links
Pick a second link as many inches along the chain as you need for shortening, away from one of the free ends. Completely press out its rivet farthest from the free end; set aside the short piece of removed chain. Double-check that your rivet removal will create a free set of inner plates to snug inside the outer plates at the other free end. Pull the chain off the front chain rings to remove tension, letting it dangle, and insert the free ends of the chain in the rivet tool with the partly inserted rivet in the outer plate lined up with the inner plate holes. Rotate the handle to press the link through the holes. If you have a chain with a quick removal link, attach it to the free length of chain without using the rivet tool by aligning its outer plates with the free ends of the chain and pressing in its reusable, or new, pins.
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