I've never done it. Just made sure there's a good continuous grey ring around the seat, and declared it good to go.
Perhaps I should next time though, for the little time it takes.
Yes, same here. But not too wide band that will decrease the valve sealing pressure according to what I have heard. Between 1mm to max 2mm on both valve and seat.
The valves should have an extra angle cut just over the grey band towards the stem to allow better flow at low lift. 30 degrees back cut. Why not from the very beginning? I had it on my first setup of valves after tuning. Later replacements did not get that.
I had problems last time with rust inclusions that had occurred during long time of no use. I did not spray the cylinders and valves with thin oil before and during the long hibernation.
I kicked the engine around 1-2 times a year to avoid pistons to become stucked. No thoughts about corroding seats. I found out after the head was off. I had to lap very much with old valves to remove the rust dots in the grey band, then lap the actual valves. Unfortunately no seat cutter available that 1 seat really needed.
