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I understand the difference, it sounds like a cam side check is a good way to verify whether there is any valve top cupping. I use .012 on the valve side what should the cam side feeler clearance?

if the valves are original, one or more of the valve stems is probably worn and the adjustment should be done to .008 on the cam side

Quoting from the Mye28 FAQ. At .012 you're using the common ground between early and late. Up thru 81 M30s were spec'd at .010-.012, 82 and later was .012-.014.

But what if the lobes are fittin to cups on top of the vales, the clearance would be too much. Is there a good rule on cam side clearance checking?

You can replace the eccentrics if they have flats. I set mine at .008-.009 inches on the cam side, and once I've done the whole engine I check each one again. I'd rather spend a few bucks and replace the eccentrics that are starting to flat, than have to adjust them again within 6 months because a new flat spot has formed.
The valves are supposed to be free to rotate, so the stems "shouldn't" get cupping, but they do. So if you measure from the cam side, you'll get the true measurement.

Of course the valves rotate. A perfect environment for an eccentric to nest within a cup on the top of the valve. The eccentric is circular and hits the geometric center of the valve stem.

Seems like the idea of cam side measurements are not in many of our toolboxes...?

If the eccentrics wear grooves into the valve stems they're not going to rotate anymore, making the problem worse. I only ever measure from the cam side, valve side is too unreliable.

So what measurement is being used for cam side checks? That is what I am trying to determine. What is a good cam side lash setting for a B35?

Note: The diagram is exaggerated for effect

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Anyone have a cam side feeler thickness to suggest?

I set my cam side lash to .008-.009 inches on my M30B28
The rockers on all M10/M30s have a cam-to-valve ratio of of 1.298.
So if the specified valve measurement is supposed to be .012, then .012/1.298 = .009 at the cam side.
Later M30s had slightly more clearance, your M30B35 should have more clearance than say the M30B28. Adjust to your liking but the ratio is key.
Check out this article:
http://www.bimmerfest.com/forums/showth ... p?t=487113

.009 is what I had been seeing as well, it does sound a lot better measured that way.