Sounds like the head or barrel or both have warped. We have had that in the past on some race motors...
Best to see if they are flat is to rub them on a flat surface with some sanding paper, you can use fine, something like 400, move the head/barrel in a figure 8 movement a couple of times while rotating the part 90 degrees each time you complete a figure 8 movement.
If the surface if flat then you will see sanding marks everywhere and if not the sanded parts will highlight the high spots indicating that its not flat anymore.
Last edited by Alzazorq on Fri Mar 25, 2011 10:34 am; edited 1 time in total