So, I'm new to working on cars and I have a 4.3l vortec in an 01 sonoma 2wd. I've done all the work myself, learning in the process. I recently changed the lower intake manifold gasket and didn't properly align the distrubor when I put it back into the truck. So, my timing skipped. Lucky me. I assumed all I would need to do was set the engine to tdc and put the distrubor back in properly this time. Engine won't crank by hand, in which case I would have to assume it seized. I have been told by a few different people now that it sounds like the timing chain probably snapped. I was just wondering if this is what is most likely has happened or if there are other possibilities.