Trusting the Sniff Test...

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How long did it run before the damage occurred? I would have expected to see a lot more piston damage. I see the damage to the cylinder port - that is the intake port, right? Looks like something was sucked into the intake.
View attachment 769670

Had run the saw for 1/2 hour, maybe. It quit and when I tried to start it I felt it catch and then would not budge. In hindsight, I wished I had taken the carb and exhaust off first. Muscled the head off which explains the damage to the intake port.
 
As others have said that saw doesnt appear to be straight gassed at all. Looks like you broke a ring and that's what caused your problems.
Also RTV is not gasoline resistant and is not the thing to use on anything that comes in contact with gasoline like a base gasket.
 
In the future if you're not sure, dump the unknown fuel into the lawn mower can and make up a fresh batch of 2-stroke mix.

"waste" a few ounces of 2-stroke oil --- OR --- rebuild the top end on a chainsaw

Wasting a few ounces of oil is both easier and cheaper than doing an engine rebuild.
 
Not passing the sniff test for sure. I think something else happened.

I suspect that the locating pin broke or backed itself out, allowing the lower ring to rotate. Once it rotated enough, it grabbed the port... and the rest is history.

It is possible that the ring overheated and broke due to insufficient/no lubrication, but I would expect to see more wear on the piston and cylinder wall if that happened. The lack of wear makes me believe that the above hypothesis may be more likely.
 

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