I have a 27hp Kawasaki in a Exmark I rebuilt about 500hrs ago. When I started it there had a funny ticking noise in the motor. So I ran it until last year when it reved up and wouldn't't idle own. I tore it apart and found the governor ,water pump gear and this little part on the back of the cam and cam was destroyed. I could see a place by the cylinder where something was hitting. I Got new parts and started it and the noise is still there. Valves are adj. at .006 .Please can anyone tell my what this noise is so it doesn't't happen again. Is there a shim on the front of the cam?