Chains do not stretch! People talk about chain 'stretch' as if the chain were a piece of elastic! This, of course, is not the case! Chain links come in pairs, an 'inner' link (with a hole at each end), and an 'outer' link (with a pin at each end to fit through the holes in the inner link). Now, as the pair of links turns around the sprocket the pin in the outer link rotates in the hole in the inner. This is where the wear occurs. Right on the internal moving parts.
If you 'split a link' on a worn out chain you can see the wear as a step on one side of the pin where it has worn against the side of the hole in the inner link. Add the steps together (one for every pin in the chain). That's why your chain has 'stretched'. You may also notice that the other side of the pin is dry and rusty. You may even wonder why that is...
Well, modern 'O' ring chains are assembled in oil at the factory with an 'O' ring sandwiched between the two side plates at each end of the pin. This seals a small amount of oil inside with the moving parts. However, the rubber 'O' rings have a tendency to grip the metal chain side plates as the link turns around the sprockets. If the 'O' rings become dry this grip increases. This is known as friction and it has several effects; first, lots of engine power is wasted turning the friction into heat. That's why a dry chain runs hot. Meanwhile, to compensate, the viscous (free flowing) oil sealed inside the link flows between the metal and rubber to try to ease the friction in the dry contact area. This can only continue until the internal oil is used up. Even so, on a modern X ring chain in the very worst conditions and with no maintenance at all, this can be up to ten thousand miles. That's why some manufacturers give you ten thousand-mile guarantees on their chains.
But eventually the internal oil will run out, then, suddenly, the wear quickly sets in. The 'O' rings become visibly thinner and the chain starts to 'stretch' like chewing gum until, usually less than a thousand miles later, you have to replace it. Now split that link and have a look!
Dryness creeps in from the outside of the 'O' ring at the point where it meets the metal plate until it meets the internal oil. But, as long as the 'O' ring has a little oil on it's outside, dryness and friction are kept to a minimum and the chain can last almost indefinitely.
Spray lube helps but it does not penetrate between the 'O' rings and the side plates once the propellant has dried. That's why spray lubed chains seldom last more than 20,000 miles.
The best way to prevent wear is to apply a little oil to the 'O' rings frequently . This case was proven conclusively by the original Loobman chainoiler. The unit used a single sided delivery system (S.S.D.) with oil being fed to only one side of the sprocket. Centrifugal force carried the oil out to the chain as the bike was ridden. In the test the 'O' ring chain achieved 27,000 miles from new before wearing out. The chain finally lost it's internal oil and wore out simply because the 'O' rings wore out on the unfed side.
So we started working on ways of getting oil to the inside 'O' rings. We kicked many ideas around. We tried increasing the oil flow and relying on 'splash-over'. We tried thinner and thicker grades of oil. But our tests showed that, while these methods can work they are a little 'hit and miss', not very reliable and usually require high oil flow rates.
In our earlier test the S.S.D. system had been feeding the oil to the one side of the sprocket and had fed the 'O' rings on that side perfectly. It followed that, if we could feed the other side of the sprocket simultaneously then we would also feed the 'O' rings on that side equally. This is what the Loobman D.S.D. system achieves. Oil is fed to both sides of the sprocket and reaches all the 'O' rings in the chain.
Unfortunately, to date we have not been able to run a complete mileage test although a new chain on a 600 Yamaha using a D.S.D. system reached 40,000 miles before the bike was involved in an accident. However the chain and 'O' rings still looked like new.
While many users have commented that the Loobman system is simple, quick, time-saving and in-expensive to buy and to use. Only a few have commented on the real benefit of greatly increased mileage from their chains. But these tend to be the 'high mileage' guys. Professional riders, couriers etc.