[Jim Brierley]

It sounds like you have checked all the normal things that usually cause that kind of problem. So I would do a compression test first, then I would check the cam timing. By removing the #1 spark plug, and finding TDC (actual TDC, not just by the timing pin) Both valves should be moving as you rock the engine back and forth from TDC. If both aren't moving, the timing gear is probably stripped, or never installed properly. Good luck!