Hello I just bought a pair of Harley WLA flathead cylinders with valves. But it was dissasemled. Now I do not know which valves are exhaust and which are intake. How to differentiate them? I think these valves are not oryginal but are in very good shape so I can reuse them. Two of them has flat surface and two other a little bit concave. Maybe you can halpe me diffrentiate intake and exhaus valves?