tackelhappy wrote: So why do you think it is necessary to replace it ?.
Stretch is the easiest way to measure the wear on a chain and predict when the chain will break. Kawasaki have determined that you can run the chain safely until the stretch on the chain goes to 1.9mm over 20 links (128,9mm service limit - original 127mm length of 20 links) Doing the math 1.9mm/20 links is .095mm per link or .0037" of stretch per link. So lets round it off to 4 thou per link.
What wore? The plates rotate on the pin so either the bore holes in the plate got bigger or the pin diameter got smaller and if the hardness of the plates and the pins are similar they both wore to some degree.
What are the consequences of running with a slightly longer chain? 2 things, every time a link plate engages with a tooth because the chain is longer the plate of the chain will now slide down the face of the tooth which will increase wear and you can see this on the teeth of the camshafts just like the notching of the teeth on the nylon gear. Have a look at the resales on EBay. They all show this wear I'm talking about (in the pics). The more the chain grows in length, the more aggressive this wear gets.
The other consequence of running with a wore chain is that it retards the timing of the cams. You'd have to take some measurements which would involve a dial gauge to determine top dead center of the crank and a degree wheel to check the cam shaft position, but you'd probably find the exhaust cam retarded by (and this is a guess here) possibly 5-7 degrees and the intake cam by even more maybe 6-8 degrees since the distance from the drive gear to the intake cam gear is the distance of the drive gear to the exhaust cam gear plus the 17 links between the 2 cam gears.
Also, the more slop in the chain the more opportunities there are for vibration. Remember that this drive system is not a continuous steady load on the chain like there is on a chain drive motorcycle between the wheel on the road and the transmission output gear but more of a cyclic load due to the fact that the cam lobes need to be pulled to the top of their peak then snap over as the cam lobe down ramp allows the valve to close at a given rate. This loading and unloading gets really jerky due to some lobes loading up as others are unloading. Just try rotating a cam by its self and you can see what I'm talking about.
All the chain manufacturers have master links or rather connecting links available. They can be tricky to install properly. There is a tool required to peen the pins. Some that are available are $30 and others are $150 dollars. All that's important is that the pin gets peened such that the side clearance is reasonably tight and not too tight. As you start to peen the pin you're yielding the steel of the pin and there's a bit of feel to this. Think of trying to push a car across the parking lot. You lean on the car increasing your force on the car until it starts to move, then once it starts to move you apply constant pressure on it till it get to where you want it. Same thing happens when you yield steel. You're applying increasing amounts of force until it yields and moves.
Just as an added note, I found on the chain that I removed from my KZ, on around or about every 5th link, the side plate had a VERY slight etching (could have been a laser etch)of the capital letter "M" which suggests to me that Morse manufactured that particular chain.