I just replaced the cam chain in my 2000 400EX. After reassembling, the quad started right up and ran good. The only thing I noticed was oil burning off the exhaust (where it meets the cylinder). I thought it was just burning off oil that was spilled when I had the head cover off, but realized that oil was leaking internally (clutch side exhaust only). I took apart the head cover again and reassembled with a different gasket, but the problem continues. I can see that it is leaking oil internally, as there is smoke coming out the exhaust.

I did not remove the cylinder or take apart the valves when I replaced the cam chain. I also confirmed that my cam gear marks were in the correct locations. Compression test results are the same as before I replaced the chain (122 psi). The engine runs smooth, so I don’t think that the valve timing is off. Has anyone ever seen this before or do you have any ideas as to how I can further troubleshoot? Thanks!