Moto Grand Prix
Join Date: Nov 2012
Location: Darkest Pulteneytown
Seizures which mark the piston at around gudgeon pin height are typical of engines that have been detonating, usually caused by bad mixture tuning and/or bad riding (low rpm slogging).
Many designs of piston have no "flat sides" at the gudgeon pin ends. An example is the in-house Triumph piston, used before they switched to Hepolite.