Now you have me scared to take my bike to have valves done by a stranger. I've always wrenched my race car engines no problem but something about a bike engine scares me for some reason like I can't do it or I'll possibly screw it up. Is it like setting valve lash on a solid roller or hyd roller setup? I'd adjust the lash between races at the track I'd gotten so good at it.
Shim under bucket is a direct action between the cam, and the head of the valve. The valve lash is set with the shim, under the bucket.
lobe>bucket>shim>head of valve
Clearances are checked the same way as any other valve train -- a feeler gauge has to check the clearance between the bucket and the cam, when the cam is not acting on the bucket.
Changing the clearance, is done by removing the cams, taking the bucket off the head of the valve, and changing the shim to one of a different thickness. If you need more gap, the shim has to be replaced with a thinner one. You can't check to make sure the adjustment is correct, until you have the cams re-installed and torqued down correctly. Writing down what the gap was to start with, measuring the shim that was in the bucket to start with, then finding a shim that is the proper amount thinner to install is all slightly fiddly and requires a LOT of attention to detail.
The process goes quicker, the more times you do it...... getting to the point where you are comfortable getting inside the valve cover already is a fairly good sign.
Not too much more to learn, there.
It really comes down to whether you have already dropped a valve. Nothing but greater damage to the motor will occur if it is run any more without fixing this.