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Chains on derailleur-equipped bikes often do not have master links. Every link is the same. In order to remove a chain, a special tool is used to push one of the friction-fitted rivets most of the way out.
One needs to be careful not to push the rivet all the way out, because it is nearly impossible to get the rivet started back in its hole. To reinstall one of these chains, the rivet is pushed back into position with the same tool, and then the chain is manually flexed laterally to free up the link. Some chains, such as Shimano's Uniglide, use replacement rivets, or 'pins.' On these, you cannot trust the friction-fitted rivet to stay put after replacement, and so must replace the rivet.
Master links are two-part or three-part special links that can be separated and put back together by hand or with a pair of pliers.
Ubiquitous on bikes with a single rear sprocket, they were never used on derailleur-equipped bikes in the past. However, new versions will fit through derailleurs and are reliable. These are becoming increasingly common on modern bikes.
When changing the length of a chain, it is usually done in two-link increments because chains consist of pairs of inner and outer links. A very rare device is a half-link, which is an outer link on one end, and an inner link on the other.
Chains need to be lubricated to avoid rapid wear, and make riding quiet and efficient. Worn chains stretch, and this in turn causes rapid sprocket wear. When chains and sprockets fit properly, multiple sprocket teeth bear the load. When worn, one tooth takes all the load at any given moment, leading to even more rapid wear. When a small rear sprocket is very worn on a derailleur-equipped bike, the chain will skip over the teeth in hard pedaling.
When replacing a worn chain, the sprockets often have to be replaced at the same time, or the skipping or rapid wear will get worse.
Lubrication is more of an art than science. Many manufacturers offer chain lube. Some are better than others. None are perfect. Some are too thin to provide adequate lubrication, or wear off quickly. Others are thick, and collect dust. When the dust mixes with the lube, it turns black and can make a mess of anything that it contacts, which is often one's clothing.
Whatever lube you use, if you put on too much, you'll have a mess. Not enough and your chain will be less efficient. It may also be noisy and prone to rust.
When lubricating a chain, it is not necessary to put oil on every link. Just lube a few links, and within a few miles, the oil will redistribute throughout the chain.
A bicyle maintenance book published in America in the 1970s offered some amusing incorrect advice. In the United Kingdom, "paraffin" can mean "kerosene," a thin, flammible petrolium-derived liquid often used for cleaning parts. The American author must have read an English book that said 'clean your chain in paraffin.' He then went on to describe in detail a procedure he must not have tried, because it was sure to fail miserably: He told his readers to melt paraffin wax in an old coffee can, soak your chain in that hot wax, then reinstall the chain on the bike.
Although I had my doubts, I had to try it, and found that my wax-soaked chain was so stiff I had to manually free every link. I still had hopes that perhaps this was the perfect, non-messy lubrication. After all, wax is good for zippers. But no, the wax chipped away, leaving my chain high and dry within a mile.
Chains should be inspected periodically, since when a chain breaks, it can be a serious let-down. The most common time for a chain to fail is when pedalling hard, and if the chain suddenly lets go, it can be such a quick change of pedal position that the rider will fall awkwardly off the bike.
To inspect a chain, turn the pedals backward on a derailleur bike, or forward on any other bike, while watching the links go by. Do it again while watching the other side of the chain. At the same time, run your thumb and fingers over the chain with a rag or in a gloved hand, feeling for any rivets out of place. The most common chain problem is a rivet that is not fully engaged in the side plates. The rivet may be displaced to one side, or the link may be expanding outward. Also look for cracked side plates.