First off, I would like to thank everyone for all the input and help. You all made me want to look closer and I noticed this, the finish inside the crankcase has been flaking. I have attached additional photos for more ideas. I have definitely rulled out the straight gas. I have had this thing apart for a few days and there is still liquid oil from the fuel mix visible. I dont think there would be had it burned up on straight gas. See the pics below.
coyote, in your original post you said the damage looked like some detonation photos you found (Madsen’s?). For some reason you tossed it out to the board for opinion… and as expected you get near every conceivable opinion.
Bad gas… too much water in it
Straight gas
Ethanol
Heat seize
Not enough oil in the mix
Detonation
Pre-ignition
Lean seize
Piston corrosion from sitting with water on it
Casting flaw
Wrong spark plug
Fuel octane too low
I think you can pretty much rule out straight gassing and not enough oil as the cause, your pictures show plenty of oil residue on the crank, rod and inner piston around the wrist pin.
A wrong spark plug should be easy enough… it either has the correct plug screwed in or it don’t.
Pre-ignition is doubtful, should be more damage, like something broken.
Piston corrosion from sitting with water on it? Hmmmmm, that’s an interesting notion, one I wouldn’t have thought of, but I don’t see any other evidence (such as rust) in your pictures… still, it’s an interesting notion.
Both lean seize and heat seize are possibilities… except that that eroded-away/blasted-away area on the piston corner indicates something else got the problem started.
Some believe that eroded area looks like a casting flaw, to me it looks like it’s been blasted away by detonation (and the associated heat). Detonation is normally initiated because of too much heat and pressure for the octane level of the fuel… not necessarily abnormal heat, but once detonation starts the engine temps rise rapidly. The detonation began blasting away at the piston and increasing temperatures, once the damage reached the ring it froze. And once the ring froze… So yeah, bad gas or low octane or ethanol or a combination of any of the three could have initiated the detonation… but without testing the fuel for octane level, ethanol content and water you’ll never know for sure.
Somewhere in this thread you indicated a belief that the guy was running ethanol-blended 87 octane fuel… and the internal engine damage (in my opinion) looks like detonation was at work. Maybe a richer carb setting would’ve saved the saw, maybe… we’ll never know. I will say that ethanol has been long known to attack metal and engine coatings (like in your picture of the crankcase)… but again, that ain’t necessarily proof, just more evidence.
Fix the saw, maybe teach the guy to tune it just a hitch on the rich side, and strongly suggest he run a higher octane fuel… preferably ethanol-free if he can get it.