Seized engine forensics..

Finally disasembled Juniors's engine (fz600/radian0) Because it seized last summer. Now it's 'Riding weather' and the Kid wants his Bike running.
Cylinder removal irevealed perfect condition Bores.. Ring end gaps only slightly beyond specs..ring lands, ditto... with NO evidence of any kind of Sieze damage.. Very confusing. Some carbonised oil on valves & piston tops So heat was definitely present. Cyl head seems to have passed 'too much' oil, likely worn out guides although they measured acceptably during the previous teardown. New (non OEM seals were installed).. Obviously those were Crap.
Will be reinstalling Cyls pistons and head from a 'known good engine'. Will also insert new valve seals (Yamaha this time.. Pricey though).
Hopefully all will be well.
Junior is worried that the damned thing will seize yet again.
Hopefully not ..and frankly I.. Do Not.. understand ..why.. this one did and I've been 'fooling' with engines for more than 3 decades.
BUT theres always something new?
Anyone have experience with Heat issues with these things?

 

Could be the cam bearings that are siezing up, and not the pistons at all?

Rich had that problem while rebuilding his X - I'm sure he'll chime in soon.

 

Interesting thought... thanx. there was 'some' galling evidenced in cam bearings but very minor and possibly pre-existing ?.
As further Info: after the seizure event we had the thing running and it made Lotsa Smoke.. a steady column of oil smoke out the ex.
Made me think there were either no rings or no guides left.
Obviously the rings are still there.. Have not yet opened up the valves tho.

 

Heat usually results in a hole in the piston head or badly scraped cylinder bores. How does the bottom end feel? Any major slack on the connectors where an insert may have spun on the crank? I would also check the wrist pins. Heat could have simply bent one and that is holding the engine. Or it may be as simple as a piece of chain guide jamming the crank.

 

No there is NO evidence to point at and say AhhHa..would be happy/relieved to find damage.
ALL that has been looked at (cept head which currently remains untouched) is looking like a V healthy engine.. stranger and stranger.