I lapped my valves and got good results testing both off the engine (pouring alcohol in intake/exhaust chambers and waiting to see level unchanged) and on (cylinder leakdown test). However, as soon as I reinstalled the cams and turned them a few cycles to open and shut the valves, I lost the seal and they were leaking again, which could be confirmed by placing a hand on the intake opening. Most leakage was on intake.
I am trying to explain this. Could it be that there was some lapping residue (lapping paste) inside the valve shaft that got into the seal/seat area after opening? Or could it be that the springs got disrupted from the initial position by moving and now they won't close shut? Or the rotation of the valve out of seal? Should I expect that all of these deviations are normal reassembly occurrence and will go away by by breaking the engine in?
UPDATE: The same effect occurs when I go through about a dozen open-shut cycles of valves manually, not with cams installed but by pushing the valve tappet with the rubber end of a hammer handle while holding the hammer by the head. After I do that, I disassemble the valve and put it back together -- without re-lapping it !! -- and it sits fine again while they remain unopened. This makes me suspect it happens because the springs/plates/stems are stiff and unbroken in and it may fix itself by breaking the engine in.