i've got a TB 108 that started as an 88 with the race head that has another odd problem a while back the exhaust vavle got bent so i replaced the valves, springs, valve seals etc and while i was at it threw in the stroker crank. after i got it all back together i started it up and it ran perfect no leaks smoke.. nothing. then after i rode it on my freinds track after about 10mins it started burning oil out of the exhaust. i figured maybe i didn't push the vavle seal all the way down on the guide so i tore it back down and checked it only to find it was fine. i cleaned all the oil out of the chamber and reassembled it to have the same thing happen again runs ok for a few mins then starts burning oil. all the oil passages have the correct seals in them and when i reassembled it i used a new head gasket. so my question is if all the seals are new and the valve seals are ok where is the oil comming from? the only other thing i can thing of is that possibly when the exhaust vavle got bent that it also bent the vavle guide and its leaking around the guide? the piston rings are all in spec and spaced properly and the motor had good compression. any ideas?