I have 24000 hard KM’s on my 2007 DRZ400sm with stock muffler with powerbomb, hotcam intake, with MX-FCR and 3x3, I do regular check of valve spacing, say once every four months of riding, always need to make a small change to one of the valves clearances. To me the bike runs fine from what I can tell power wise, but nothing to compare to. -I would like to know when or how do I tell when, it’s it time to replace all valves & springs? Or just valves?? -In addition how to replace the valves, I understand how to get the valves physically out and in, but is there anything that is needed or should be done to do with seating new valves, or is it just a straight replacement? -In the future I would like to do a big bore, would the OEM valves and springs be acceptable. Alternatively, is there a more suitable make of springs and valve required of a future big bore?