Some of the 2008 and newer bikes have a new tensioner, they will not fit in
early bikes as the hole in the cylinder is too small to fit.
As for why the new tensioner, so far no reason, the one above failed at 12,000
miles I am told, as for the reason,spring was weak.
Please send me any information you have on your bike and the cam chain
tensioner,Model GT/GV and size 125/250/650, year and mileage, new or old and good or bad.