2003 XR 400. New piston. Putting it back together, I have everything aligned, crank and sprocket. I can put the cam in with the lobes up or down. Manual does not say one way or the other. So, sure, I'm on TDC. But it seems to me that my spark will be right one way and 180 out the other. Can someone explain to me how the cam should go, and how I make sure my spark isn't 180 out? Thanks very much!