Larry,

I would check the injectors. Loosen the flare nut (the nut that connects the injector lines to the injector body) on the top of one injector at a time to see if the noise goes away. Fuel oil will leak out and the engine will miss fire, but that's OK, you are looking for the knocking to stop. If you find that the knocking on one cylinder stops, that is the one with the bad injector. If you want to be sure it is that injector, switch the suspect injector with another one and see if the noise follows the suspect injector. If it moves, its a bad injector. If not its something else.

If its not a bad injector, you might check the valve lash with go/nogo gages to make sure that were set right. Valve timing is determined by the wear in the timimg chain. It can't be off a tooth or the engine would not not turn because the valves would hit the pistons. A rebuilt engine should have a new timing chain in it so valve timing should be right on zero.

You will need a 1 1/8 or 27MM deep socket to remove the injector. This socket will also work on the crankshaft nut to turn the engine by hand to adjust the valves.

P E H