Valve Train Noise

Here is the update White016 asked for. A retired mechanic neighbor pulled the timing chain cover since the knock seemed to be coming from there. As some of you know, accessing the timing chain is not an easy task. Tip: instead of dropping the axle as some sources suggest he lifted the engine off the front mounts to access the hidden pan fasteners. Once all the covers were removed, he could inspect all valve train parts and all rod bearings. Unfortunately, nothing obvious showed up. Since 20 hours had been invested to get to that point, I asked him to replace the moving parts (timing chain, tensioners, cam sprockets, valve lifters, exhaust timing solenoid); but I didn’t expect any of that would solve the problem. He also replaced the water pump, thermostat and main seal. After everything was put back together the knock was still there. I filled with high octane gas and some Seafoam; but the knock persisted after a couple days. I tried one last diagnostic – fuel injectors. For this, I removed the air cleaner resonator and bridged the two air ducts with a 7” length of pvc pipe. This allowed the engine to run while giving access to the 6-pin injector harness connector. I devised a set of 6 wires to jumper between the male and female halves of this connector. I then sequentially removed each of the wires while the engine was running. After removing the first wire, the engine ran a little rough; but the knock was still present. Eventually I pulled the jumper to #1 cylinder and the noise stopped. The engine was as quiet as when it was new. I hope this expensive/time-consuming trial and error helps someone in the future.