I have a 03 yz450f not sure how many hours. She runs like a top. The valves were redone when I got the bike. Im just wondering how to tell when the top end needs to be rebuild and if I would need to split the case and purchase a new crank aswell. Can the cylinder be bored or do you have to buy a new one. I know how rebuilding motors goes I think. Pull the head bore the cylinder oversized rings slap everything back together. Will it be fine like that? how bought a complete overhaul. The above but replacing crank bearings instead of buying a new crank. How do you rebuild these things without spending 400 on a new crank is my question. Also can I use a compression tester to see when the top end needs to be freshened up. If I freshen up the top end wouldnt the bottom end explode?