Hi, I bought a yz450f, it had 80 hours on it since rebuild. I did like 5 hours of riding and then decided to check valve clearances as I was not sure how the bike was maintained. As I took the caps off I noticed these: cap bolts loose, intake cap bent, journals badly scratched overturned cam cog. As I bought the bike really cheap and was not aware of when the head was fully rebuilt I decided to buy a new one. A brand new head for my bike is on its way from the states but I am wondering what was the direct cause of that seizure? As I don't want that to happen with my new one. These are my bets: *The guy who sold me the bike told me the oil was replaced every 30hours *wrong torque on the cap bolts *overheated engine *other serious mechanical failures like bad oil pump?? are they prone to failure? As I drained its oil, it was nearly pitch black, nothing exceptional, paper oil filter was clean.the engine worked, wasn't noisy, checked the oil pressure by loosening the bolt in the head, the oil was pumped. The man who sold me the bike assured me it was rebuilt, he changed the piston, crank, intake valves, cam chain. As I took the head off, I saw a really nice cylinder, piston and a tight conrod which I do not want to replace. My question is would you strip down this engine before installing the head which cost me nearly 900$? I badly want to cut down the costs as the head has already stretched my budget and would like to install it without inspecting the rest as that will perhaps involve bearing and gasket replacement& others. I thought about taking off the right and left side covers, clutch then take a look at the pump and if fine put the head on. My question is would you put the head on without stripping it down?