Normal
Perhaps keep an eye on ebay for a cheap replacement head. That erosion will let combustion gases to where they are not supposed to go. like this http://www.ebay.com/itm/02130-Yamaha-YZ250-YZ-250-1991-Engine-Motor-Cylinder-Head-/170922033391?pt=Motorcycles_Parts_Accessories&hash=item27cbbf40ef&vxp=mtr
Perhaps keep an eye on ebay for a cheap replacement head. That erosion will let combustion gases to where they are not supposed to go.
like this http://www.ebay.com/itm/02130-Yamaha-YZ250-YZ-250-1991-Engine-Motor-Cylinder-Head-/170922033391?pt=Motorcycles_Parts_Accessories&hash=item27cbbf40ef&vxp=mtr
