I took mine apart, and reassembled it after compressing the springs way more than before. I assembled it with all screws in 3 full turns (or 3 1/2) I can't remember. When it was assembled, I fixed all the screws that weren't in the center of the cube. If your middle layers are really bad, it's because the screws are tightened uneven and the core is bent/misaligned. Make sure the screws are in the exact center. You can fix this by tightening or loosening. Right now my cube is excellent. It does pop when I scramble it with random moves at breakneck speeds, but not during solves. Right now it's the best 4x4 I've ever tried.
EDIT: I finished putting on the stickers and it sucks now...I took half of it apart and it looks like it's time to clean it out . I lubed it a ridiculous amount about 3 or 4 days ago, and I've not been solving it, so it makes sense.
EDIT AGAIN: This cube is definitively not worth the money. Way to much maintenance and work put into it. The results aren't so great. The cube locks up a lot, and pops and falls apart. I average 1:00 - 1:03 on my maru if it doesn't misalign. My average skyrocketed to 1:20 on the x-cube. The cube is just way to flimsy and tight (yet pops and falls apart). The reason I said it was the best 4x4 I've ever tried, was because I had to set my standards
very low for this cube. Anything fingertrickable was considered good.
It's like a medical drug. You can cure the problem, but it creates symptoms, sometimes worse than the original problem. There are no misalignments, but it pops, it's expensive, it requires a ridiculous amount of patience and work, and is rough/bump/ locks up a lot.
Edit again again: Ok, yeah, it's over. I'm extremely angry at how much time and effort and money I put into this. I was playing with my Maru and my average dropped 20 seconds (from x-cube), but it still misaligns. Biggest waste of money ever. I guess I'll just have to buy a Dayan 4x4 to use. No misalignments and reasonable turning. Oh wait, I spent a bunch of money on this cube, so I guess Dayan will have to wait.
