I have a 1997 k2500 Suburban with the 7.4 vortec. It is a 290,000 mile engine and I was recently doing some work to it. I put new injectors, valve cover and upper intake gaskets, distributor, plugs, wires, and a fuel presssure regulator. This engine was fine before and the only reason I had done this work was because it was cranking for about 5-8 seconds before it would start. When I put everything back together, I got the timing as best as I could (I do not know how to properly time these newer engines) and started it. Immediately, the engine was shuttering and I could hear what sounded like a lifter tap. It was idling very rough and after about 4-5 min a louder knocking sound started up. I immediately cut the engine and checked the oil for metal, and there was none. I am simply baffled at this as I didn’t touch anything when I had the valve covers off. My only two ideas are this. 1) it is not timed right, and I need to figure out how, or 2) the old distributor had some wear on the gear, and possibly the cam has the same wear and isn’t working right with the new distributor. Any help on this would be greatly appreciated. Thanks.