I 1655 gas that has a knock at about 17-1800 RPM, it sounds like it is near the front of the engine. The throttle arm on the governor has a pulse that goes along with the knock.  I have checked the rod bearings and they are all good. The governor has been updated.  The engine has about 45oo hours on it. I am wondering it the timing gears could be the problem... Has anyone had any similar experience..Any help would be appreciated!!