In the world of new cruisers, chains and sprockets have just about disappeared, at least as far as final drives go, so you may question why I'm devoting this much ink toward their maintenance.
Simple. Despite the current popularity of belts and shafts there are quite a few older cruisers and standards running around with chain drives on them, and I'm willing to bet a cold six-pack against a warm glass of milk that at least 50 percent of you own one of them.
It's A Chain ReactionSince most of you have at least an understanding of how chains and sprockets transfer torque from the engine (or more properly the transmission) to the rear wheel, I'll forgo explaining the obvious parts of the process. However, it's worth noting that in many respects a chain is fundamentally a series of small bearings joined together in a long string, and like any other bearings they need to be kept clean, well lubricated and properly aligned if you expect them to do their job without complaining.
The chain roller fits over...
The chain roller fits over the chain bushing to make up the roller link. The pin link holds adjoining roller links together to make up the chain. All those rolling and pivoting parts need a lot of care.
Maintain That ChainDirt is any chain's biggest enemy. When road grime makes its way into a chain it works like grinding compound to wear out the rollers and bushings. Some riders inadvertently aggravate the situation by overlubricating the chain. This allows the excess lube to form a sticky mess that acts as a dirt magnet, and wear is actually accelerated. Periodic cleaning prevents that from happening and also makes it easier to inspect the chain for wear and damage.
Chains should get a major cleaning at least once a year, more often if you're riding in dirty or dusty conditions. Ideally the chain should be removed from the bike, given a good soaking in solvent and a scrubbing with a bristle brush, then hung up to dry overnight before being lubed and reinstalled. That's a lot of work, especially if the chain has a riveted master link and if, like me, you're averse to performing hard labor when you could be out riding.
You can use commercially available...
You can use commercially available chain cleaners or a stiff parts-cleaning brush to get the job done, but a specific chain-cleaning tool makes it a lot quicker.
My preferred method is to slather the chain with a degreaser like Gunk, then give it a good scrubbing with a Grunge Brush chain-cleaning tool. I finish up by rinsing it down with the garden hose, then drying it with a clean rag. You can substitute WD-40, kerosene or any commercial chain-cleaning product for the Gunk and use an old paintbrush or nylon bristle brush instead of a gen-u-wine chain-cleaning tool, and the results will be just as good.
So why not just blow the thing off with a pressure washer or steam cleaner and be done with it? The answer is because it'll ruin a chain-especially an O-ring-type chain-before you can say "Holy smoke, parts-counter guy, that's an expensive replacement chain you've got there."
The high pressures and temperatures created by power washers and steam cleaners will wash the grease right out of a standard chain, which is bad enough, but at least you've got a fighting chance of getting it back in there. However, when those types of washers are used on an O-ring chain, the heat and pressure not only remove the lubricant but can also deform or damage the O-rings. Unfortunately even the best aerosol chain sprays won't be able to force the fresh lubricant past the O-rings (damaged or not), so what you'll be left with is a clean, albeit dry chain that's going to have a very short and unhappy life.
If the link moves more than...
If the link moves more than halfway off the sprocket tooth, the chain's worn out.
Normally I'd recommend relubricating the chain ASAP to drive out any residual moisture and protect it from the elements. But before you do, let's take five minutes to go over the basics. By the way, you can inspect the chain anytime you feel up to it; it's just a lot easier to do it when it's freshly cleaned.
Inspection = Detection
First give the chain the once-over. Make sure it's still relatively flexible by pivoting a few links. If the chain is really stiff or has a seized link you may be able to loosen it up with some chain lube, but in the long run you're probably better off replacing it right then and there. Acid damage from an improperly routed battery-vent tube is also a fairly common problem, and unfortunately anything significant will mean replacing the chain.
To inspect the chain for wear, grab it about halfway up the backside of the rear sprocket and give it a tug. If you can pull the chain more than halfway off the sprocket tooth, it's shot, and quite possibly so are the sprockets. I should mention that while this isn't the only way to check chain wear, it's the most reliable method when the chain is still attached to the bike.
Physical damage is usually...
Physical damage is usually obvious. These rear-sprocket teeth are starting to show chips and wear, and the chain has cut down into the shoulders. These countershaft teeth are starting to hook-it's not terrible yet, but this sprocket is on the way south.
Worn sprockets are usually pretty easy to spot-look for hooked, chipped or eroded teeth and, most obviously, missing ones. If any damage is found, replace both the sprockets and the chain. If the sprockets look good but the chain is worn, go ahead and install a new chain. Just don't expect it to last as long as the original, and on the next go-round be prepared to replace the chain and sprockets.
Next to dirt, improper chain/sprocket alignment is probably the most frequent cause of premature chain failure. Take a look at the chain and sprocket from the top. The chain should be centered on the sprocket tooth. If the chain runs to one side, the chain and sprocket are misaligned. This can usually be corrected with the chain adjusters, but in some cases you may have to align the wheels to get everything back on track. (See "Tips for the 411," Oct. '06). By the way, if the alignment appears radically off you may have other problems, so make sure the wheel spacers are in the correct position and the wheel and swingarm bearings are in good shape.
 |  The chain rollers should be...  The chain rollers should be centered on the sprocket. | |