Here is a bit of history leading up to the possible problem. A buddy rode my 02 kx 250 (without permission) and caused a 4 point seizure by not letting it warm up(he denide riding it said it probably happened just sitting in his locked garage... yeah cause that happens all the time). Anyways i pulled the cylinder head off and the piston was broken. I went to extreme action sports(kawi shop where i live) and ordered top end rebuild kit and asked them to hone my cylinder. They did but the skuff marks were still there so away it had to be sent to have the cylinder re crome plated. 20 days go by and finally it returns but the heat has everthing removed off it. I'm decent with a wrench but putting the power valves back together was a challenge if i had taken them out it would have been a different story but if i don't see it come appart it isn't that easy. Now i'm pretty sure i put them together right but not 100%. Anyways i finished putting the top end back together and have broken the piston in but now i hear a knock from the engine. It is pretty constant but blends in more the louder the engine runs. A freind and i listened to the engine with a stethiscope and we've determined that the noise comes at the top of each stroke(when the piston is closests to the spark plug). Now i'm not sure if it is a normal noise(me just tripping out) me skrewing up putting the piston in(not likely), he power valves making the noise, or another thing i hypothisized was possibly play in the connecting rod caused by the prior seizure making the sound. $600 later i might just be tripping out but better safe than sorry so any input would be greatly appreciated. A special thanks to my good "buddy" for costing me $600 to get it back to the shape it was in before he rode it not buying me the aftermarket pipe and silencer that i had planned to.