Shall we have a look inside? Two 6mm Allen screws and the RMZ valve cover comes right off for valve clearance inspection.
And here we have it. You simply put the timing mark on TDC and both of the cam lobes will be on their sides at the same time. Then you use the appropriate feeler gauge to slip under them to see how tight or loose they are. Motion pro makes a valve feeler gauge that's really slim and is supposed to be easier to slip down in there. I had no problem using my standard gauge.