You can make adjustments, if you can really call it that. There are no adj. screws, but the cam followers can be changed out for new ones thicker to take up the slack. Nissan has them of varying tolerences for this. Problem is the cams have to come out to do it, and that's a major pita. They all make a tad bit of noise after some years. Best leave them alone unless you are losing performance. Pricey repair!
Traded 10/10/11 for a 2012 Hyundai Genesis Track Coupe.