Recently bought a 1030 advertised as having a bad engine. It's running great, no bubbles in the radiator, no water in the oil, and minimal blow-by. The problem is a knock in the upper end of #6 cylinder. I pulled the rocker covers today and adjusted the valves. All were very close to spec, and the engine is real clean inside. The knock is most obvious at low rpm, but is always there. Definitely in the head, and not lower. I can feel a noticeable difference in the #6 injector line in conjunction with the knock. Do I have a bad or sticking injector? Can this cause the knock? Any help is appreciated.