Oppy mechanics manual says:
However, do you think, re-facing the valves and seats both to 30° is advantageous? Because of:
Moreover, the exhaust valve head's upper most part is rather thick compared to the intake valve head. I guess, this is due to better heat transfer enhanced by more material. On the other hand, I definetly believe this thick valve head reduces gas flow. See lower valve on this Picture; it really sticks out:
What do you think, should I "flatten" the head by grinding off some material?
The Oppy mechanics manual states minimum thickness of valve head(s) to 1/32" - this would be at least half of what it measures right now.