Where does that ridiculous notion come from?
addendum: You're confusing pre-ignition with detonation.
OK then, I like your backbone. Somebody not afraid to speak out. You're wrong but I admire your gall.
Where does that ridiculous notion come from?
addendum: You're confusing pre-ignition with detonation.
This didn't happen for no reason out of the blue as has already been said.
This is going to happen again unless the cause is found.
There were several hints that something was wrong before it wouldn't run anymore.
You’re right, figuring out what happened is a good idea… fixing something with out fixing the cause is senseless.
Let’s take the issue of ethanol…
Just ignore statements like “ethanol is not the cause of this lol. I run ethanol in my saw daily, so do most other people. probably straight gassed.
Most other people? Well not ‘round here. Besides, that’s like saying “Drinking and driving won’t get you arrested, I’ve been drinking and driving for over 30 years. Probably flipped the cop off.”
What about detonation?
Well the damage from detonation in a two-cycle engine running 12k+ RPM is a lot different than what you’ll see in a four-cycle running 7k Rpm. Detonation is the spontaneous “explosion” of the fuel after the spark plug fires… initiated from heat and pressure. First, the spark plug of a high-performance two-cycle (like a chainsaw) is normally centered over the piston, and the controlled burn happens relatively fast… remember it’s turning over 12k. Detonation is most likely to initiate on the exhaust side, were heat is the highest. The damage from detonation happens three-fold… at the point of “explosion”, at the point where the two flame fronts collide, and at the point where the shock wave rebounds against something. Because of the fast combustion rate in a high-performance two-cycle engine, the flame front from detonation may only travel one millimeter or less before it collides with the combustion flame front. All of the damage is localized at the edge of the piston, where it “blows away” that edge or corner… and shortly after that it gets to the ring… and shortly after that… (and that’s surely what I see in your picture).
Octane?
A lot of guys are gonna’ argue with me, but 87 octane fuel is horrible for any high-performance engine… including chainsaws. And something most guys don’t understand is that the addition of mix oil lowers the octane of the fuel even more (yeah, that’s right; oil has a lower octane rating than gas). “Octane” is a measure of the fuel’s resistance to “detonation”… once ignited (such as by a spark plug) it burns at pretty darn close to the same rate regardless of octane rating. Yeah, I know a lot of guys run 87 octane fuel… but that’s just like the “drinking and driving” thing above… they just ain’t been unlucky yet. And remember, the octane rating is minimum... meaning it may be higher, but never lower (supposedly). You may go for months, or years, actually buying 88, or 89 octane at the "advertized" 87 level, but suddenly you get 87... and then you lean on the saw...
So if you put it all together…
Low octane fuel, more likely to detonate.
Ethanol-blended fuel causing an engine to run hotter (even if tuned).
More heat, more likely to initiate detonation.
And then what happens when you get fuel with more than the “advertized” 10% ethanol?
At least by running a 91-92 octane fuel you give yourself a bit of margin for error… but at 87 octane you’re already on the edge.
Was ethanol the root cause? Who knows for sure… but I’d bet it was a huge contributing factor at the least.
He should also be running 32:1 when milling. Milling generates a lot more heat in a saw...
Damage looks a bit much for over-lean mixture.
I'm leaning toward straight-gassing. And forcing the cut until it gives up in a cloud of smoke.
Tuned too lean
low octane fuel
Plug too high heat range
To much alcohol in fuel
Lean condition caused by vac leak
Or any combination of the above.
Using more oil in the mix will rob power from the engine, causing it to work harder.
Actually, the opposite has been proven true, due to better ring sealing. Ask around and see how many experienced millers are running 50:1.
Staight gassing would cause damage all the around the piston and cylinder. Steve
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