You clearly shouldn't have been under the valve cover at all. There is a thing called "Valve lash" that tells you how much space there is supposed to be between the rocker arms and the valves it is measured in Thousandths of an inch with special "feeler gauges" each engine has its own specs. Get a repair manual for your car if you want to work on it don't just go "tightening things up" if you don't know what you are doing. You only adjust rocker arms when valves are in closed position, you over tightened and now valves aren't closing at all. The really stupid part about all this is you were probably attempting to "adjust away" lifter rattle, which has nothing at all to do with valves. Always read up on what you are wanting to repair before you take a wrench to your car.
