[Sid Squid]

The valve clearance check is scheduled every 15,000 miles, so at 20,000 miles it's slightly overdue, yes it is entirely normal to find some clearances out of tolerance - that why it's a scheduled check. That said the SV is known for not needing a lot of adjustment, that doesn't mean it's never needed though.

Generally speaking exhausts close up and inlets open a bit, so your finding the exhausts a little tight is not something that can be ignored. As you're going to be removing the cams I'd reset everything to as near the middle of the allowable range as is possible, that way it's odds on the longest period until it needs doing again.

Every time the inlet valve opens it receives a nice cooling rush of incoming gas, and when it's closed it dissapates heat through the valve seat, even though that's a small area for conducting away heat - every little helps - in short the valve itself has an easy life, and thus wear in the opening mechanism commonly outweighs the wear to the valve - thus the clearance often opens up a bit. Exhaust valves however don't have such an easy time, they get and stay very very hot, their primary way to dissapate heat is the thin ring of the valve seat, and a little up the stem, everytime the long suffering exhaust valve opens it gets fried with gas at/near combustion temperature - typically 300-700C - thus in the case of the exhaust, the valve tends to wear more than the opening mechanism, hence the clearance reducing.

Also we have a nasty Catch 22 - if the clearance becomes significantly reduced, (or worse still if there's no clearance and the valve never fully closes), the valve spends less of the already small amount of time that it should do closed, thus it never disspates the heat it should do and can literally melt, this is called burning a valve, no surprise there, and you really don't want to get into that.

A round of applause for your exhaust valves please - the hardest working bit of your bike, full stop.