I have to disagree with the last part of your order of events. The combustion gas blow by, as evidenced by the discoloration on the piston, could not occur in the very short period of time (a few seconds, if that) that the crankshaft continued to turn over after the needle bearing failed, and the top of the piston hit the cylinder head (which should have also damaged the valves). This engine would have died almost instantly.
That degree of combustion gas blow by takes a significant amount of running time to build up. I'll say it again... this combustion gas blow by is the result of piston rings that were not well seated during the initial run-in of the engine when it was new.
I'm still curious as to how you are certain that the needle bearing cage was cracked from day one? (sorry, but I have to keep asking this question)
look i stooped the bike because i felt the knock from piston that hit the cylinder head.
evidence for that is the smashed surface near the KYJ and IN on the other side.
you didn't looked at all the pictures in the link, i posting another picture from different angle(which i take from the whole album from post 1).
let say you right about the rings the how can you explain the clean drained oil from previous services?
why the decoration occurred only on 2 sides under the piston and not on the whole diameter of the piston?
i am certain because it shredded the brass cage ,but the needles wasn't worn the bearing contact surface is not worn, nothing only shredded cage which did all the mess.
when the engine is working the cage don't carry any loads. how could the cage be shredded without any significant wear on other bearing components?
now some messurments
PISTON PIN O.D 17.00 mm which is on standard reference of 17.00-16.994, the service limit 16.98
PISTON SKIRT 75.94, service limit 75.89
CYLINDER I.D 76.08 , service limit 76.04
crank shaft to journal bearing O.D 34.000 , service limit 33.975
it looks like the engine would last the weak points is: the piston which coating degrading considerably fast.
and the shims of the valves which all 4 gone offset by 0.05mm