i am assembling this frame as well, I had an issue with the top headset bearing that has a too tight fit with the frame. It is possible to install it, but it is very hard to remove, even with pleny of grease applied to the bearing outer surface. I've measured the bearings and they are 52mm outer diameter. I'm going to try it with a 51.8mm outer diameter bearing. Longteng shouldbe more precise on this kind of details, they are providing an headset that is not the best fit for the frame.
