All About Motorcycle Chains, Belts, and Drive Shafts

The MC Garage final word on final drive.

Motorcycle chains, belts and shaft drive
Anatomy of a Chain
It appears pretty simple at first glance, but look closely and you’ll see your chain is composed of quite a few components, all of them carefully designed and precision made. Here are the parts of a modern sealed chain.©Motorcyclist

Drivetrains don’t get a lot of credit. The engine—which makes the power that hurtles you down the road and produces that sound and feel that bring a smile to your face—gets all the glory. But if that torque weren’t transmitted from the engine’s output shaft to the rear wheel you wouldn’t be going anywhere. And for that reason this month’s MC Garage is dedicated to the final drive in its three forms: chain, belt, and shaft.

Chains are far and away the most common form of final drive today, and while the idea of a roller chain can be traced back to the sketchbooks of one Leonardo da Vinci, the first motorcycles weren’t chain driven but belt driven.

Belts were originally cut from the most durable material available: cowhide. Leather belts tended to slip, wear, glaze, and break, so they were quickly phased out in the first part of the 20th century in favor of chains and drive shafts. Look around any dealership though and you’ll see that belts are back. Belt materials and manufacturing technology made big enough strides that by the 1980s belts were tough enough to be used on bikes again. Belts are mostly used on cruisers, but BMW, Buell, and eBike manufacturer Zero have employed belts on sportbikes because they offer some distinct advantages over the ubiquitous chain drive. For starters belts don’t need lubrication so they’re cleaner. Belts are also quieter, offer a long service life, and—besides the occasional visual inspection—require very little maintenance.

If belts are so great, why don’t we see them on other types of bikes? Packaging and difficulty of replacement are the biggest drawbacks. Today’s synchronous (toothed) belts are as strong as chains and not much wider, but they can’t wrap as tightly so they need a larger countershaft pulley (and correspondingly large rear pulley to attain the proper gear ratio) than a chain setup. And when it comes to replacing a drive belt, the process usually entails removing the swingarm.

Drive shafts must be the best form of final drive, right? Those who have them on their bikes certainly think so, and shafts have been the final drive of choice for BMW since 1923. "The historical use of shaft drive is primarily for longevity and minimal maintenance requirements," Communications Manager at BMW of North America Roy Oliemuller says. Drive shafts are nearly maintenance-free, impervious to the outside environment, and—barring any sort of freak failure—will last the life of the bike. All strong benefits, but shafts are also costly to build, heavy, and sap more power than other final-drive systems. And unless the manufacturer wants to build and fit two sets of expensive, power-robbing bevel gears, drive shafts are best reserved for engines with longitudinal crankshafts. Shaft-jack under load used to be an issue as well, but clever linkage arrangements have almost eliminated it.

That brings us to the roller chain, the most prevalent form of final drive. As with most things that are mass-produced, cost is a huge factor, and chains and sprockets are cheap to make. They’re also compact, fairly durable, easy to replace, offer easy gearing changes, and are the most efficient means of power transmission. Yes, chains require regular cleaning and lubrication, tend to make a mess of things, and wear out much faster than belts or shafts, but every form of final drive is a compromise.

Chains are in essence just a series of plain bearings linked together via inner and outer plates. Unsealed chains were the norm for decades, but they were difficult to keep lubricated so wore quickly and necessitated regular adjustment and replacement. Then someone came up with the clever idea of permanently lubricating the parts of the chain that need it most—the pins and the bushings that rotate on them—and the sealed chain was born. In sealed chains grease is drawn into the bushing by means of vacuum when the chain is assembled, and then rubber O-rings squeezed between the inner and outer link plates seal in the grease and seal out dirt and water. Sealed chains offer considerably longer service life compared to their unsealed counterparts.

You’ve likely heard someone refer to an old chain as having stretched, but “chains don’t actually stretch,” says Farrah Bauer, marketing manager at RK Excel America. “What happens is called elongation, and it’s the result of wear removing material from the pins and bushings.” This slight increase in the tolerances between the pins and the bushings increases the chains pitch (the pin-to-pin distance), in turn lengthening the chain.

As the chain wears and the pitch increases, the rollers grind the sprocket teeth into the telltale shark-tooth shape. Given that chains operate at just 1/6 of their tensile (breaking) strength, it’s far more likely for a severely neglected drivetrain to lose all of its sprocket teeth rather than snap a chain. You can usually see pretty spectacular examples of this scenario on the wall at your local mechanic. The chain and sprockets will give you lots of warning as they wear, including noisy operation, jerky power transmission, and vibration. Not sure if your chain is worn out? See the “Is Your Drivetrain Toast?” sidebar below.

Since the most critical parts of the chain are packed with grease, there's no need to douse your sealed chain in lube. All you're really doing when you spray your chain is lubing the rollers (which, despite their name, do not rotate a bit once they make contact with the sprocket) and keeping the O-rings moist and happy. So when you lubricate your chain aim the straw at the overlapping portion of the link plates along the lower rung of the chain. That way centrifugal force will aid the dispersion of the lube on the chain. Lubing the outer edge of the chain at the rear sprocket is convenient but not very effective. Want more detail? We have a comprehensive video on the topic of chain cleaning and lubrication (watch How To Properly Clean and Lubricate Your Chain here).

motorcycle sprockets
Sprocket Wear
New on the left, worn on the right.©Motorcyclist

IS YOUR DRIVETRAIN TOAST?

No matter how religiously you clean and lubricate your chain, it and your sprockets will eventually wear out. The easiest way to get a gauge on your drivetrain’s health is to look at your rear sprocket, since that’s the first part to show wear. Are the teeth symmetrical or hook-shaped and thinning? If they’re the latter, that’s a good sign that your drivetrain is reaching the end of its life.

Another easy test is to grasp your chain midway round the rear sprocket and try to pull it away from the sprocket. If you can see daylight under a link, your chain has elongated enough that you should replace it.

Finally, if you want to be absolutely sure you can measure for wear. Put the bike in gear and have an assistant roll it forward so the lower chain rung is taut. Then measure the center-to-center distance between 16 consecutive pins. If it’s greater than 256.5mm it has exceeded the allowable 1 percent elongation, and it’s time to renew. (This applies to the common #520, #525, and #530 chains.) Always replace your chain and sprockets as a set, as installing a worn chain on a new sprockets or using new sprockets with an elongated chain will accelerate component wear.

WILL WD-40 DESTROY YOUR CHAIN?

Whether or not WD-40 will keep your chain’s O-rings happy or ruin them is one of the most controversial topics in motorcycle maintenance. Supporters say WD-40 is great for cleaning your chain and won’t harm a thing. Critics say WD-40—or more specifically the petroleum distillates in WD-40—will dry out the O-rings, displace the grease, and ruin your chain. What’s the truth?

To begin, what is WD-40? According to the company, “WD” stands for Water Displacement, and the “40” stands for the 40th formula to be mixed up. The safety sheet for WD-40 says that it’s mostly Stoddard solvent, a petroleum product similar to kerosene. So for all intents and purposes, WD-40 is mostly kerosene. And most owner manuals actually recommend using kerosene to wash your chain.

Okay, but WD-40 isn’t 100 percent kerosene, and there might still be something in that secret formula that will cause your chain’s O-rings to swell up and die. So, to find out just how damaging WD-40 might be we disassembled a chain and dropped some O-rings into pure uncut WD-40 and let them stew for a week.

And? They were fine. Compared to the control O-rings, the parts in the WD-40 bath were the exact same size and consistency.

WD-40 won’t ravage the O-rings, but some people are still worried about it penetrating past the seals and diluting the grease around the pins. To test that theory we submerged a single assembled link in fluid for several days. After cleaning and drying the link it was disassembled. The grease was thick and gooey, and there was no evidence that the WD had even made it past the first lip of this particular chain’s three-lip XW-ring seal. To be fair, we were working with a section of brand-new chain and the chain was stationary, not in use on a bike.

Our experiments show that WD-40 will not harm those little O-rings. However, one of the chain manufacturers we contacted for an opinion warned against using WD-40, saying “we cannot recommend it, out of an abundance of caution.” Not a particularly strong admonishment, but with so many products available specifically for cleaning O-ring chains, there’s no reason to use WD-40 if you’re even slightly concerned about it shortening your chain’s life.