finally pulled my dead engine apart and found...

Pissed 'n' broke.

A sad place to be.

holy cow!!!

What would cause something like that? A seized engine due to lack of oil?

Looks like another case of lack of oil.

So in this case, what is the best action. Find a working motor and buy it? or Repair the damage? I would assume the crank is damaged as well and maybe some transmission gears? Definitely the cylinders and possibly the head? Just curious what most people would do.

There have been some people who have in this case just sanded the crank and put it back together, only to have it promptly make a clicking noise and die again.

Cranks have to be turned to within 1 thousandths for roundness and an exact diameter for which you get the right bearings and fit em in. So, dont hand sand the crank and refit, it will die in the next 10 mins.

BTW I have one of these lying about too, but mine was abuse. AFAIK, that dude ran it full throttle (dunno if he was just in neutral or actually riding) for a long time, had oil streaming out of it @ the head etc and it seized.
Cool.
Buddha.

other damage as follows:







transmission seems fine. head is also fine and is fitted to my replacement engine.
thankfully it was me who was riding it so as soon as it occured it was dumped into neutral and coasted to a stop.

as for the best action? im not sure. i need to swap the gear lever rod from this damaged engine to my replacement and also identify the nature of grinding noise thats developed on the replacement too.
i suspect the rest of this engine will get junked although i have considered polishing up the casings for a bling GS ressurection

perfect for a CR or KX 500 2 stroke motor swap?

I think that if I ever find the time to get mine up and going and then if someday this happens I am going to go for it.
Maybe you should do yours first and then do a full write up with lots of pics and video.

Maybe I am a whacko but I think an otherwise normal looking street bike with a big ol expansion chamber and kick star would be cool as heck.

IIRC I think the later model 500's were running about 60ish HP and the motor should be much lighter than the gs stocker.