All crankshaft bearings have a cage around them.Could be they had a little rust on them and then when started they tore the cage up.If the rear bearing started to get any slop in it that might be why theres scoring on the piston,pieces of metal.These usally dont just fail all the time.Do you mean you have a 2 magnet flywheel or 3 magnet flywheel.There shouldnt be 2 flywheels on one motor.Do you mean a clutch.I thought someone said here on RCU that the 3 mags are kinda like a retard or advance system.Maybe it just gives a hotter spark.