It's time to check the valves on my 03-CRF450R. I'm not a gear head by nature, but can figure most things out by trial and error. I've done the basic maintenance like oil, oil filter, tranny, air filer change on a regular basis and have about 20 to 25 hours logged on the motor. I need guidence as to what I'm supposed to look for while checking the valves. I have read all the threads on this subject as well as the owners manual, but no one really touched on the subjuct on how to do it. I'm new to 4 strokes so I'm not sure on what to look for and how to correct. I have a feeler gauge to check the clearences, but what do I do if I'm lose or tight on the valves? Shim? What does it mean to Shim? Can someone take me step by step. You can call me toll free or I can call you, or just reply here. If you want to call me just reply & I'll give you the number. Thanks!