From the J&P Cycles Blog Archive

If you're looking for a better way to transfer power, you may wonder if there's an option to the classic roller chain. Belt-drive systems are popular with many Harley riders, but they don't seem to be an option for a lot of folks, especially in high performance or racing situations. A toothed belt's power limit is directly related to its width. That might be okay for a stock 60 hp (or 90 hp) Harley but above that a drive belt would have to be very big, to the point of widening the whole bike, to make it fit. Also, unlike chains, individual belts are not adjustable, so for the foreseeable future we're stuck with our old chains.

The last big step in chain development came in the '80s with the mass introduction of the O-ring sealed chain. Those little rubber rings have solved what was the chain maker's biggest headache for many years: Loss of lubricant. The load bearing pins and bushings that enable a chain to bend over a sprocket have precious little oil to keep them happy. As if that wasn't enough, high centrifugal forces that occur when the chain turns around the drive sprocket throws away the oil.

Chains wear because they lose lubricants. The advent of the O-ring chain enabled the chain to keep its oil inside and stay lubricated where it counts for long periods. The lubricant in a modern O-ring chain is not ordinary oil. It contains plenty of synthetic additives that, for example, help it withstand the enormous loads that develop during a first-gear burn-out. Friction-reducing additives don't really help because friction is not the issue. A lubricant's film strength is what keeps the metal from touching and wearing. The moment it is not there, wear escalates.

Tips for Proper Chain Care

Even the cheapest chain without O-rings will last a surprising amount of time with proper care, meticulous adjustment, and oiling at 350-mile intervals. Heavy gear oil applied with a brush is what many racing teams use, but this is a messy proposition and best only when the chain can be left to drip away the excess overnight. Most people spray on chain lube, which is good as long as you wait the required 20 minutes to let the solvents in the spray evaporate and leave the thicker lubricant on the chain rather than on one of the tire's sidewall. Chain grease is not so efficient. It cannot get into the tight clearances between moving parts and the most good it can ever do is keep the chain's side plates from rusting in the winter. Chain oil's main enemy is high running temperatures. The running temperature of a chain ideally should not exceed 160-degrees Fahrenheit. Above that, chain lubricant starts to thin and the chances of it seeping out past the O-rings increases. Eventually the film strength drops.

This brings up the matter of chain adjustment or rather, chain mal-adjustment, the main culprit for "well-done" chains. Surprisingly an over-tightened chain is a far worse crime than a loose one. Informed riders know that suspension movement increases chain tension, and what is a fairly tight chain at standstill becomes impossibly tight when the suspension bottoms. These added and unnecessary tensile loads can exceed the chain's capacity and the increased friction will raise the chain's temperature sky-high.

A new, too-tight chain can, in no time at all, turn into history. The best way to check chain tension, the one used by many race teams, is to ask two of your biggest friends to sit on the bike and compress the rear suspension to the point where the wheel spindle, swingarm bearing bolt and the front chain-sprocket centerline are all in line. That is the point of maximum chain tension. Or you can compress the bike's rear end with a ratcheting tie down. Free up-and-down movement at the middle of the chain's bottom run should be about half-an-inch (13 mm) with the suspension compressed.

Of course, a loose, dragging-on-the-floor chain is not too good either. A loose chain will rub on many static parts of the bike such as the swingarm rubber buffer and frame spacers. Besides, with the chain's ability to saw through anything in its path, the added friction will again raise temperatures. The sprockets will likewise suffer. A loose chain will "ride up" into the higher and weaker areas of the sprocket teeth and slowly bend them into a wicked hooked shape. Proper tensioning as explained above is the remedy.

Also, proper tensioning means a straight and true running rear wheel. A cockeyed, sideways rear wheel will place uneven stress on the chain, making one side of it work harder than the other. That is bad. A quick check can be made by sighting the chain's top run, back to front. A badly misaligned rear wheel will show as a notable kink in the chain's run line. For more exact results you can pick two eight foot (2.5 meters) straight-edged wood boards and place each one on either side of the bike, about 4" (100mm) above the ground. On a properly aligned wheel, the edges should touch the rear tire sidewall and leave equal gaps on both sides of the rear tire. Adjust your chain tensioner accordingly.

Race teams mechanics don't crawl on the floor with wood planks. They use a compass with two, long sharpened points to compare the distance between the swingarm bearing pivot and the rear wheel spindle. On a dirt bike, without a silencer getting in the way, a measuring tape will be just as effective.

Even after all this straightening it is worth checking that the chain runs even, centered on the rear sprocket. A missing 1mm washer somewhere may cause one side of the sprocket to make contact with the chain. If after some mileage one side of the rear sprocket gets shiny near the teeth it means that the front and rear sprockets are not properly aligned. A few shims or washers here and there can cure this.

The 500 or more pieces that make up a chain lead a very unglamorous life. On the other hand, failure of just one of them means a sidelined bike. Proper care is not too hard on body, soul or pocketbook and is definitely worth it. If your chain is misaligned and distressed you will certainly feel the difference in ride quality after a well-deserved chain care session.