See my previous post here in this section on this item.

  Now!!!  There has been several that the piston hit the backplate at the bottom of the stroke.  That is only with the stuffer style backplate installed.  Some engines it barely touched and others it hit quite hard. (hard enough to cause damage).  Fox Mfg was contacted on this problem (I sent them an engine back with one that hit quite hard) and they recognized the problem.  All new units shipped from the factory will have corrections made to the pistons.  Any out in the field can be shipped back to the factory either in the engine or separately and Fox Mfg will make the fixes at no cost to the customer.  (other than the shipping I would imagine)

  Bigiron