Question....valve covers

[GMCjunkie]

I finally got my truck back together so that I could actually start it and see if I fixed the tapping sound by replacing the valve cover seal and the exhaust manifold seal. I started it up and the tapping sound is louder than before. Heres my question, can I run my engine with the valve cover on the passenger side off? Also, if this is possible, what the heck do I look for? I already looked at the valves and rods, none appeared to be cracked or bent and none of then had more than the most slight play in then. Also, open for suggestions...

Thanks so much!!!!

junk