Nice work, good luck and keep posting. What if anything did you I do make the 500 setup burn?
Wrist pin, rod? Etc
Thanks

I’m sorry Go oddy I’m not understanding your question. Are you asking me what did I do to make the Engine blow up? If that is your question I don’t know the answer besides running it wide ass open trying to keep up with these high powered machines I was chasing

Sorry for the confusion....no not how you blew it but how you built it originally?

I'm sure as heck no expert, but you had to loose compression for a reason. Thinks look good in the pictures. Could you have a stuck ring not seating properly? Why would the plug look so crappy?

It looks like the top ring may have rotated past the locator pins? Take the bottom ring off the piston and push it into the cylinder. Measure ring-end-gap and post back.

Also measure your current piston-to-cylinder wall clearance. I'd say if the clearance is <8thou you might get away with a new piston and just a hone, but is doubtful. Think about your piston costs, hone costs, and consider going to 90mm. BTW on a CR500 sleeve you should be able to get all the way out to 91mm on Wiseco. that's a lot of bores/years.

Finally on your O-Rings. This one is easy.

The inner O-Ring you should use measure the diameter of the slot on the dome, and the thickness of the slot. You can refer to various sized O-Rings at http://www.mcmaster.com. You want to be very careful with your selection however, because with the heat I would highly suggest you get Viton O-Rings for chemical and temperature resistance. Look here:
https://www.mcmaster.com/viton-fluoroelastomer-o-rings

The outer O-Ring is going to be EASY. Either you can try to lay it out and measure the diameter, ordering O-Rings 3 times, which isn't a bad idea... OR, McMaster sells O-Ring cord stock where you can make your own O-Rings. Look here:
https://www.mcmaster.com/viton-fluoroelastomer-o-rings
All you need is the diameter, and then cut the O_Ring to length. I'd use Permatex Water Pump and Thermostat RTV at the joining end to attach the O-Ring back onto itself. Clean cut the ends with a razor blade. Hell; I'd use that stuff to dress the entire O-Ring honestly. Let it dry for a few days before coolant is added. This is how we do it with large 2-cylinder JetSki heads with the outer o-ring.

Can you line the piston backup the same way you took it out? Keying off the piston damaged section will tell you where to look and see if the ring got snagged. If you just replace the parts, it may happen again if there is a problem with the cyilider.

morning REDMAN,

My first thought from looking at pics is Ring flutter.
My second thought, Check your exhaust port chamfer and cord width
My third thought Plug, kinda normal as it goes away. I would say you lost the ring before your trip.
My fourth. look at your exhaust flange. This will confirm

Remember your were running it with a coolant issue a while back. It is a good idea when this happens you pull the piston and change the rings. What happens is the pressure loss between the ring land can and will cause ring flutter and fracture of the top ring or break the top of the piston. Look for evidence of combustion marks on the bottom of the top ring and its groove. Also measure the lands width on the side (90 degrees from exhaust center). You should notice a some sort of taper in the groove from ring twist. This will happen if ring flutter and loss of pressure took place. If you do find this you may need to change ring end gap on rebuild to help with pressure between lands. Measure the distance down the cylinder to the change in wear mark on the cylinder. This will give an idea of peak cylinder pressure and timing for your fuel set up. Then check the from that mark to exhaust port opening. Get me those numbers along with cord width. Take a hard look at the exhaust port roof chamfer. Look at the book and get an idea of how the taper is in relation to the ports width. Wider the width the more aggressive the taper in an elliptical port. The ring is at static presssure at the point from port open to port close. So with any ring twist in the land from flutter can lead to port snag.
Or heck it could have just went boom. no matter what look hard at the port and read up on presure balance between the ring for seal and anti flutter at (high) rpm.