3.4 Engine Knock -Stuck Valve?

just did IMG job on 2001 venture 3.4.....had to put a helicoil in one the valve spring bolt holes in front head...changed oil,new plugs and wires,etc.....the enginehttp://kona.kontera.com/javascript/lib/imgs/grey_loader.gif
(http://www.2carpros.com/forum/2001-chevy-venture-2001-34-engine-knock-after-img-repair-vt414361.html#)is now knocking while running...pulled the front valve cover and retightend the lifter bolts,still knocks...i know i did not mix up the rods or drop anything in the engine...is it possible to break valve spring or make lifter stick by over torque..the bolt pullled the threads out when i was tightening it....spring does not appear broken...any thoughts would be extremely appreciated....thanks...jim

And the knock is where in the valve train, or lower end? Isolate the valve by feeling or listening to each rocker with a long screw driver if in the valve train.

like he said listen to see if you can find the one valve or lifter that's knocking. i use a battery operated head set to listen and it really dose help on this set up.

ok, got the head off and can see where piston was hitting valve...please look at pics and see the wear marks and let me know if it is ok to put back together.(after getting head fixed of course). the mark on the piston is on the upper right inside edge...on valve it is upper left,first valve (from L to R)...thanks

Piston looks ok, but what happened here?

just a screw up on my part....helicoil wasn't down far enough(below the slit at top of lifter bolt hole) and lifter didn't line up right