I have a 2006 YZ250F. I've decided to tackle my first 4 stroke top end (I have experience with 2 strokes). After about a week of research, I've decided to dive in, take my time, follow my manual and online resources (TT), and ask questions along the way (hope you guys don't mind...). I tore down the bike to the point where I have the least confidence, and seems to be the most confusing: the valves / timing / head. Most of my questions are more along the lines of someone verifying my understanding of how things work. Here are my questions: 1. When I turn the crank and, and look through the “viewer hole”, it almost looks like there are 2 different timing marks. One looks like an “H” and one looks like an “I”. I’m assuming the “I” is the TDC? Is the "H" a timing mark? 2. I’m wondering why the motor has to be at TDC to disassemble the cams? Is it because at TDC there is no pressure on the cam lobes? 3. The manual talks about loosening the cam cap bolts in a “criss-cross” pattern, or you can cause damage. Is there an exact science to this? I’m thinking that there are 6 bolts on one of the cam caps. I guess I’m looking for a little more guidance in this area. Is there a right and wrong way to remove the caps? 4. Here is my understanding of timing (correct me if I’m wrong): When the piston is at TDC, your flywheel timing mark should be aligned (looking through the viewer hole), along with the punch mark on each cam sprocket should be “flush” and align with the top of the head (each punch mark on the outside edge of the head. Am I correct that the “E” and the “I” stamped on the sprocket have nothing to do with the actual timing alignment? I’m just looking at the little “punch mark” in each sprocket, correct? 5. When I took out my crankshaft cap and viewer cap, there was a little moisture in there. Is that ok? It looked like there was some dampness on the inside of the cap, and a drop of something that looked a little “milky”. Is that ok, or is there a different issue? 6. Just to verify, I have to remove the cams to remove the head and cam chain, correct? 7. Before I tear it down, I want to have a firm understanding a valve clearance. Here is my understanding: When the piston is at TDC, there should be a clearance of between .10 mm and .15 mm between the cam lobe and the “pad”. If the clearance is less than .10mm or greater than .15mm, I need to change the pads. Am I correct in my understanding? Again, this is a bone stock 2006 250F (low hours), that has never had a valve adjustment. I'd like to thank everyone for there help! I've gotten a lot of great info from you guys!