I just finished my 4th check of valve clearances at ~34K miles. Here is the history of my valve adjustments.
8K- no adjustment
16K (performed at 20K) - Adjusted front cylinder exhaust valves from .07" to .08". Spec is .07 to .09" for exhaust valves.
24K- no adjustments
32K (performed at 34K)- Adjusted rear cylinder exhaust valves from .07" to .08". Adjusted one rear intakes from .05 to .06" to match other intake. Spec is .05 to .07" for intake valves.
Points of interest I noted during the valve adjustment for everyone to consider.
-All four of my exhaust valves have now been adjusted once, the fronts at 20K, rears at 34K. None of the clearances were out of spec, but were getting tighter and needed to be centered. I was happy with my rear exhaust valves at 20K and 25K (actual miles when checked), but not at 34K.
-Through trial & error(s) I found an easy way of setting the valve is to view the change in the adjustment screw slot position with the minimum and maximum spec feeler gauge inserted and then set the screw to the mid position and lock it. For example, the exhaust valve spec is .07 to .09", so I inserted each of those feeler gauges and tighten the screw until snug, then check the adjustment screw slot position. The change for the adjustment screw slot position is extremely small, I found that it was typically less than the difference from 12 o'clock to 1 o'clock (30 degrees)....that is the entire range for the valve to be in spec. So then I was aiming for a 12:30 slot position (~15 degrees) and locking it down. Check, re-check, torque, check, re-check, repeat if needed. Watch the adjustment screw slot position as you tighten or torque the lock nut and if it moves, most likely have to start over.
-As much as I would like to extend my valve checks I just cannot justify it. Not because I'm paranoid that the valves are suddenly going to be grossly out of spec, but because of all the other maintenance items that can be performed in conjunction with the valve checks. I'm talking about the fuel hose, coolant hoses, breather/air hose, and electrical cable inspections that need to be looked at under the gas tank & surrounding the throttle bodies. I've seen 1 fuel hose rub that needed protection, 2 cable/wiring runs that needed better routing or relief, 1 air hose rubbed nearly 1/2 way thru, oil leaks, coolant drips, etc... Every time I do the valve checks, another potential problem is discovered. Your results may vary.