Join Date: Mar 2008
Location: Hamilton, ON, Canada
Admittedly, my experience with doing valve clearances (that I can remember, not including some old Yamaha parallel twin I did 20 years ago) is limited to three bikes, all with DOHC and 4 valves per cylinder. One had forked rockers with individual threaded adjusters for each valve (ZG1000 Concours), the second had individual rockers and shims over buckets (ZRX1100), and then the V-Strom. On all 3, valves that were out of spec when I checked them were tight. As I understand it this mostly due to valve seat wear over time.
To get looser, some part of the valve actuation mechanism would have to be wearing - cams (on the "flats" of the cams? seems unlikely), rocker arm wear surfaces (or rocker bearings), or the head of the valve stem. None of those are impossible, but they're not "normal" wear. I'd say if you find valve clearances getting looser, there's something going wrong.