This is my 1st post. I have a 2007 yz450f that I was riding when it just stoped on me, felt like it lost all power. I Opned up the valve cover to check the timing and the intake cam spun on the sprocket and made the intake vales hit the piston. The chain did not jump because it was a TDC and the timing markings were correct. I looked at the otherside of my bike to look at my lobes that were facing out like they should but only my exhaust lobes were correct witch was at 2o clock. My intake lobes were at the 9o clock position when it should be in the 10o clock. Since the intake sprocket spun it made my springs work extra hard witch broke one of them causing no compression. my fix is buying a new cylinder since it was scratched, new piston, intake valves, springs, seals and 2 new cams. to never have this happen again I will be tigging the sprocket to the cam since its only pressed on. hope my hardship helps you.