Ok I took my 400 to the shop and heres what happened, you guys think of anything i need to do: just mention! wanted to thank everyone for thier replys to what it may have been also. Anyways the timing chain jumped, bent the intake valves and just scrated the piston surface. Mechanic said its had the top end rebuilt before and the piston was in backwards.(arrow pointing away from exhaust) and that the decompressor and springs wernt in. And its a stock cam. It ran great i thought, could this happen?
So he says hes gonna resurface the piston and do something with the valve seats cant exactly remember what though, replace valves, timing chain, tensioner. This is the first time working with this mechanic and he seems like a honest guy. Just want you guys opinions on the work bieng done. Anything else i should replace while its apart or mention to him to check?

also i asked for the 450 cam chain and he said thats fine but he has heard of them wearing the cam lobes because thier a heavier chain. Anyone heard of this? i went with it anyways. hope it wasnt a mistake....

 

You can get heavy duty chains for them. I'd just replace it with one of them instead of the 450 chain.

 

When I was looking around about the 450r chains before, I thought I did see someone that said it could wear the lobes. Don't know if it's a fact, but I did see it somewhere else.