WetLeather Motorcycle Rider Information

You folks with belts or shafts can move along, patting yourselves on the back as you go. Emendation to the following text will be carefully considered.

Modern motorcycle chains are generically known as "roller chain". Each pivot between consecutive links consists of two concentric simple machine elements - an oscillating plain bearing and a rotating plain bearing.

Starting at the inside, each pivot between links consists of a hardened steel pin peened (or grooved in the case of a master link) on the ends to retain the outer links. Riding on this pin is a sintered bronze alloy bushing. The bushing is pressed in a hardened tube that has been swaged into holes in the inner chain link plates. O-rings between the inner and outer link plates retain grease inside the bushing and exclude dirt. This is the oscillating plain bearing. It is lubricated for life.

All dynamic seals, like the o-rings in a chain, leak to some degree.* Retained fluid leaks in order to lubricate the line of contact between the seal and the sealing surface. If it does not leak out the seal fries, and if it leaks perceptibly then it's no longer a seal. You do not want to try to force lubricant in from the outside because no matter how you try to clean the chain some spooge will be stuck between the o-ring and the link plates in the area where they approach tangency. This dirt will be carried into the seal surface area with the incoming lubricant abrading the seal and sealing surface causing leaks in both directions - lubricant out, dirt and water in.

Around the outside of the tube between the inner plates is a loose hardened tube. It's this rotating plain bearing that makes it a roller chain.

Chain sprocket teeth are designed to let the outgoing and incoming links roll across the tooth faces as the links engage and disengage. This allows load sharing between the adjacent teeth. Contact stresses on the dirty tooth faces are the highest stresses (relative to material yield strength) in the whole system. If the chain can roll rather than slide along the tooth as it engages and disengages the sprocket stress, wear, friction, and noise are significantly reduced.

The chain rollers are both harder and more numerous than the sprocket teeth. Wear tends to be greater in the sprocket than the chain rollers. When the sprocket teeth wear the chain links no longer load share as the chain rotates increasing the tooth loads and resulting wear.

The rotating plain bearing has no internal lubrication. It also has no seals to retain any lubricant. This is why you lube the chain - to keep the rollers rolling instead of sliding so the sprocket teeth retain their profile.

Chain stretch (wear of the bronze bushing) also increases tooth contact stress. The teeth wear to match the change in chain pitch. This is why you have to replace the sprockets at the same time as the chain to get maximum life out of all of the parts.

A lubricant film also protects the chain steel from rusting.

You lube your chain to reduce sprocket wear, power consumption, noise, and to prevent rust.

* This is why high purity gas and vacuum dynamic seals were such a PITA until the development of spring loaded reinforced Teflon seals. In fluid applications modern PTFE seals leak almost nothing, needing no lubrication at the seal lip if appropriate materials are chosen and can run dry if the speed stays low enough to keep the heat at the seal lip down. Note that this type of design is relatively expensive.

Bored at work,

Joe Lanfrankie