Lubricating your chain is certainly one of the easiest maintainance tasks for a motorcycle owner, however I frequently wonder how necessary it really is.
Are there any negative effects which can come from never lubricating the chain?
Lack of lubrication does lead to premature chain and sprocket wear, and loss of drivetrain efficiency. However, more important consideration in this case is safety.
It is absolutely essential to keep the chain cleaned and lubricated to prevent catastrophic failure that at best would result in snapped chain, and at worst can lead to binding and locking of drivetrain, which could lead to injury, death, and/or engine damage.
This informative article on chain maintenance states in regard of the chain failure due to drying out or other wear of the link seals (most modern chains are internally lubricated, but require external cleaning and lubrication as well, to keep seals fresh and reduce friction and heat generation):
The seal(s) retaining the lubrication for one or more rollers fails. Typical causes include: abrasion (such as sand rubbing between the seal and one of the plates); friction (heat generated by inadequate lubrication external to the seals as the plates rub against them); weathering and age (seal dries out, cracks), or other stresses (such as chemical exposure to naphtha or other harsh chemicals).
The primary way to keep this kind of failure from occurring is to keep the chain (and thus the seals) free of sand, dirt and other contaminants via regular cleaning, and to keep it lubricated appropriately externally as well (to minimize the friction at the seal/plate interface, and to help keep the seals in good shape).
The above advice about keeping the chain drive clean and lubricated applies to the general prevention of premature wear, and maintaining the efficiency. Even if the chain was to be thoroughly cleaned, there is no way to prevent its contamination with dust, sand, mud, salt, water, road grime and other abrasive or corrosive substances, thus some sort of protection is still necessary. And there are still moving parts in contact (rollers, and plates with each other; both with the sprockets) that create additional friction and heat if not lubricated.
Efficiency of a chain drive is a complicated beast. The studies of various aspects of it are few and far between. The most commonly cited one is the British experiment from 1930s which measured efficiency of a non-sealed bicycle chain in an oil bath under a constant power, and found it to be over 98%. However, such are the ideal conditions and rarely apply in real world (chain drive sealed inside the motor is one of few such situations). Moreover, the real efficiency is affected by the temperature (sealed-ring chains perform much better when warmed up as the grease inside becomes less viscous), speed (at, high speeds, as this publication states, “the transmission efficiency can be as low as 85% due to inertial tension”), uneven power application, and other factors.
But most authoritative sources still insist that lack of lubrication (external, as well as internal) decreases efficiency, and lifespan of the chain, ceteris paribus.
If the chain is not lubricated it will wear prematurely.The chain does not stretch but grows in length as the pins and barrels wear.This has the effect of changing the distance between the rollers.As the chain grows it will no longer match the pitch of the drive sprockets, the sprockets will wear out prematurely.If you then change the chain it will be worn by the old sprockets. What all this means is oil the chain to make it last longer.Change the chain when it is worn to make the sprockets last longer.You can measure the chain wear by putting a ruler at any point on the chain use the end of a link or the center of a pin.Look at a point 12 inches away you should be at the same point ,pin center etc.Up to 12-1/8 is ok when you get to 12-1/4 it time to replace the chain.