Valves are one part that tend to get tight over time. Mainly because the valve face is just beating on the seat constantly, and the seat wears.
Tight valves are quiet and can cause big bucks in repair bills (Labor, seats, valves, cams, etc...). Loose valves are noisy and can rob power since the valve isn't opening all the way.
I checked mine for the first time when I got the bike with 12K on it (previous owner said the bike had "hydraulic valves" and didn't need adjusting). Only three were out of spec, the rest still on the tight side of spec. I adjusted everything as loose as possible, while staying in spec (.006" on the intake, and .009" on the exhaust), and I'll let them go for another 10K.... actually, my speedo hasn't been working (broken cable, snapped in the $80 hub drive) and I haven't fixed it, so I'll check them again once I wear out the set of Metzeler Z6s' I put on at work today.
You can generally tell what condition your clearances are in by a few hints. How quiet/loud they are, and drastically tight, a noticeable loss in power... as well, a major hint to tight valves is how quick your engine returns to idle when you blip the throttle. A slow return means tight valves.
After all is said and done, it's not a very hard job when compared to other bikes (like my TL1000- all the plastics go, drop the radiator, remove the tank, then you can get at the front cylinder), and shouldn't be neglected.
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