Join Date: Jan 2007
Location: Sacramento, CA USA 96814
You are over tightening your chain. If you adjust your chain so you have 1/2" slack on it while it's sitting on the side stand, it's almost definitely getting pinched tight when you sit on it - particularly when you are riding. This will cause rapid wear and elongation of the bearing surfaces. Your chain isn't actually stretching, it's just wearing at a very rapid rate.
I destroyed the first chain on my gsxr doing just that - I would tighten it to the spec (0.8 - 1.2 inches) while it was sitting on the side stand and it would just "stretch" constantly, until the links started seizing up. Now I run my chain looser than spec, and I don't have to tighten in periodically at all.
This is a common problem.