Or, Like I said before, the cam may have jumped time due to a broken/incorrectly adjusted cam chain tensioner. Bad rings rarely cause NO compression, unless they are crystalized. That happenned to me once, when I was 15. It was 30 degrees and I jumped right on my bike and started riding like normal. A few minutes later, it just died. I got home(pushed it 2 miles), and found it had no compression, took it apart, and found the rings had broken up into little pieces no more than 1/8 inch long![img]i/expressions/face-icon-small-sad.gif[/img]I have also found that a large piece of carbon can sometimes dislodge and stick to the valve, preventing it from closing all the way.