I spend a better part of the weekend reading up on valves and now I think that I am more confused than when I started. The center intake valve '07 WR250F is the only one that has ever moved. It started with a 1.78 shim from the show room floor. I have been checking and adjusting as needed, and it is now at a 1.50 shim. I have read that 10% change is the most you should do and I am obviously past that. Is this truly the case? I have also read that I may need "head work". What exactly does this mean and is this true? Other places I have read that just changing the valves and springs is what needs to be done. Which is the case? I assume that if I need "head work" that I would send the whole head out and they would work their magic and they would also install new valves and springs. Correct? If it is only replacing valves and springs, is this something that I could complete? What tools would I need? I have no engine experience beside checking and adjusting the valves. Any insights would be greatly appreciated!