2 cycle lubrication

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A small amount of gasoline in the oil of a four cycle engine is a bad thing, but some 2 cycle engines use mostly gasoline with a small amount of oil to provide adequate lubrication. I realize they are different systems but how do they get away with this? And of course no filtering other than in 2 cycles’ gas tank.
 
Different materials and bearing types. Most modern 2 strokes use roller bearings.
 
Two stroke oil is a little different. It resists burning or it would gum up the rings and exhaust system very fast. When you see the blue/purple smoke from a two stroke, that's tiny droplets of oil in the air. The fuel/oil mixture is passed through the crankcase where it lubricates the crank and rod bearings which are roller or needle type. This kind of bearing can get by with far less oil. Some oil will settle in the crankcase where it is scavenged and returned to the intake port.
 
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Originally Posted By: WobblyElvis
When you see the blue/purple smoke from a two stroke, that's tiny droplets of oil in the air.


My old Yamaha DT175 would literally spray oil all over your back while you were riding it.
 
Also fresh oil is constantly being sucked through the engine and flushed out of the exhaust. There is no dirty oil circulating. The air filter is super important though.
 
There is also not much going through in a modern 2 stroke - my scooter has a cat. I'm currently on 1600km on a litre of oil, I calculated nearly 2000km to a litre, so still an unkown own at this stage.
 
That's pretty amazing. That shows you how old my last two stroke was.
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Doesn't this make the flashpoint of the 2T oil very important depending on the use of the engine? i.e. high revving race engines need higher flashpoints and low revving OPE low flashpoints?
 
Its much worse now with alcohol in the fuel; acids and Ethanol make polyethylene precursors, can this happen in the engine? I say maybe given my filters plugging up the past decade.
 
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Originally Posted By: ARCOgraphite
Its much worse now with alcohol in the fuel; acids and Ethanol make polyethylene precursors, can this happen in the engine? I say maybe given my filters plugging up the past decade.

What? You say you think you're making a polymer and that's clogging up your filter?

If so, out of all the goofy things people attribute to EtOH in fuel that has to be the best one yet.
 
"A small amount of gasoline in the oil of a four cycle engine is a bad thing"

Is it really? By the time the engine is up to temperature, any gasoline in the fuel will have evaporated.

You'd be surprised how many OPE engine have had or will get gasoline into the crankcase without any signs of related issues other than false oil reading due to increased volume the fuel adds while the engine is cold.
 
Originally Posted By: Burt
A small amount of gasoline in the oil of a four cycle engine is a bad thing, but some 2 cycle engines use mostly gasoline with a small amount of oil to provide adequate lubrication. I realize they are different systems but how do they get away with this? And of course no filtering other than in 2 cycles’ gas tank.


LOL it doesn't hurt anything! Back years ago when we ran racing Karts they used the flathead briggs and stratton engines (5hp variant) and with a 34mm Tillotson carb and running pure methanol, I'd get on average 4-6 oz of methanol in the crankcase after each track session on my limited modified engines! Keep in mind these little things only held 14 oz of oil and turned 8500rpms!!! They lasted quite awhile before needing a rebuild too. A little gas in the oil surely won't hurt a thing!
 
I'm surprised you'd have that much fuel in the crankcase once the oil is up to temperature. From my experience and what I've read, the gas in the oil usually cooks off when the engine is run for a while. Especially in an air cooled engine.

I agree, though that a bit of fuel in the oil is of very little consequence.
 
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