I have an 83 b100 van that my father bought new, From what i understand ever since it was new it has always had a random tapping of the valves/lifters from time to time. Sometimes it won't do it for a few hunderd miles, then again sometimes it will do it for sever hundred miles then stop just as mysteriously as it started. Is this common for the 225 with hydraulic lifters? I rebuilt the engine some years ago and installed new cam and lifters, still the same result. Also replaced the oil pump thinking pressure might have been low. No change. Any ideas anyone???