I have a 05 wr450f and the girlfriend has a 06 wr250. I just shimmed her intake valves last night (exhaust needs it soon, they are at the low end, but I didn't have 5 170 shims...) and I want to know what I will be in for in the future... How many times should the stock valves be shimmes before they are toast? What all needs done when it is time to replace them? guides, seats, springs, retainers, or just drop in new valves? Where is a good shop to get this done, if I need machine work? What are the pros and cons of using something like the po-x SS valve and spring kit? We mostly ride low RPM singletrack, though I let her rip more than the girl... differences in rebuild procedure between Ti and SS? Lastly, where is the best place to buy OEM Ti valves? (I assume TT store, but the buggers are expensive! I know it doesn't cost Yamaha that much, 1/16th of the purchase price in valves alone? I think not..) Thanks!