Firstly -

to XT660.com!
I think most of what you need to know will be in these threads:
http://www.xt660.com/showthread.php?t=53
http://www.xt660.com/showthread.php?t=32
http://www.xt660.com/showthread.php?t=55
It is all written in greater detail in the official Yamaha Service Manual, which is available as a download for XT660.com Supporters. Cost �10 for the year and there are stacks of other benefits too. Click on the links in my signature to find out more about it.