Strange that after grinding the exhaust valves you would need THICKER buckets! I would have thought you would be needing thinner ones, unless they ground the ends of the stems and took too much off. What do you think the reason for this is?
Short version: I cut the stems too short.
Old carpenter's joke: "I don't understand, I've cut it off three times already, and it's still too short!"
Here's the long version:
When you gave me the suggestion to have the stems shortened, the head had already been dropped off at AJ Cycle (AJ's uses a local machine that they have a long time relationship with.) I could have taken the head directly to the machine shop, but chose to let Alan and David at AJ's deal with the machine shop.
After I got your suggestion, I called Alan at AJ's and suggested the stem shortening approach. Alan said he'd bring it up with the machinist but the stem reduction didn't get done. When I picked up the head Alan told the machinist would trim the stems if I wanted, but I'd have to assemble, measure for the needed reduction and then bring the valves back.
In hindsight, if I had measured before I dropped off the it would have been easier, or if I had talked directly with the machinist it might have gotten done.
So after getting the head back I assembled the head and made measurements. I have a bunch of spare 0.290 and 0.295mm buckets from earlier adjustments. After the valve job I needed 5 or so in the 0.270 -0.275mm range. (Before the original disassembly of the head the gaps were at the tight side of the specs, and there were mostly 0.280-0.285mm buckets in there. So I'd say that the valve grind caused a decrease in the clearance in the range of about 0.01mm)
My idea was to grind the stems so I could use the 0.290-0.295mm buckets, and have my others for later when things tightened up a bit.
Measurements and calculations in hand I took my valves to my friend Stanley at Lynde Motorsports. (I would have had Stanley do my valves in the first place but his machines are pretty old and he didn't have a collet small enough for the BMW stems.) (Stanley has been a great help to over the years during my Airhead rebuilding period. Not many guys will invite you into their shop and turn you loose with their machines. He's a nice guy).
I used Stanley's valve grinder myself to shorten the stems after he gave me a brief "how-to" demo. Not sure what happened, but I suspect operator error. When I was zeroing the valve stem I wasn't all that careful about where I bottomed the valve stem on the grinding wheel. I should have been careful to use the very outer edge of the grinding wheel where the actual cut was being made. A slight concavity of the grind stone may have given me my error.
End result, I over shortened some of the stems by about 0.01mm.
So now instead of needing thinner buckets, I need thicker buckets.
Live and learn.