[rhandwor]

I had a Chevy and a valve guide got worn and it would run fine then the valve would twist and it would miss. With the valve cover off you could watch what was happening. When you do your exhaust manifold I would do a compression test. If you put some oil in a low cylinder and the compression doesn't change I would look at the valves sometimes a nut will come loose. They use lock nuts get a new one if loose.