Missing Intake Valve Retaining nut

The number 6 Intake valve is missing its retaining nut. My concern is where could it have gone? Could it fall into the oil pan and be sucked up? Could it be poised to jam a valve, score the cam, or something else? Should I pull the engine and find it or can I safely replace it comfortable that the nut is floating harmlessly somewhere without endangering anything? I think I know why it is missing. I recently adjusted the valves and the engine did not run well afterwards. I am re-adjusting the valves when I discovered the missing nut. My guess is that I did not tighten it properly and it backed off. Certainly accounts for the poor running since number 6 was not opening at all! :o

That could be a real mess. At least it is the intake side... if it were the exhaust side, the nut might have gone down one of the oil return tubes. I forget how large the oil return orifices are inside the intake valve cover. Good Luck.