I'm looking at doing my intake valves on my 450. I was looking at the thumpertalk store under the OEM stuff and have a couple questions. 1. What do I need to replace? - Valves (for sure) - springs? - retainers? - seals? - seats? - anything else? 2. is having to lap the valves typical or something that rarely needs to be done? I guess I have one more question. When doing valves, is it best to do intake and exhaust at the same time, or only when needed? I still have good clearance on the exhaust side. Thanks for the help!