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How does the piston-cylinder surface get lubricated ?

I jetted my street-legal 220 rich for running at high speed for extended period of time because I thought that running cooler is less wear and tear on the engine. But then, I read somewhere that running rich will actually causes extra wear on the cylinder wall because (1) engine temperature is too low to burn up all the fuel in the air-fuel mixture and (2) the unburnt fuel washes off the oil on the piston and cylinder wall. Is this apply to 2-strokes?

Am I doing more harm than good by running the bike rich like the piece says? Or is it urbend legend?

Rich as in fuel/air, or rich as in more oil in the mix?

Anyway, a two stroke is pretty unique in how it lubricates the top and bottom end. On the pistons upstroke, the reeds are pulled open and fuel air mix is pulled into the bottom end, on the downstroke this air fuel mix is forced into the top end via the transfer ports, where it is then ignited and the process gets repeated. So the cylinder is lubricated from the top and bottom by the same mixture. I find it unlikely that a rich fuel mixture in a 2 stroke is going to wash lubrication from the cylinder, but I would like to read said article all the same.

R u talking fuel to air(jetting) rich or oil to fuel rich 32-1?
The oil in the fuel lubes everything except the tranny.
I wouldn't jet really rich due to power loss and fuel consumption. Get a nice dark plug color use good synthetic oil and run it. Just use all or nothing throttle input at high speeds to vary engine rpms. Think of a chain saw. Runs wide open all day long. Just on or off the throttle like a switch. . Bra app. Just my thoughts.


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Yeah, I mean rich in fuel. Because the piece was talking about 4-stroke street bikes.

He said he jetted it rich so it sounds like he's talking about fuel/air rich. Only problems with rich jetting is power-loss, more spooge and other deposits from the unburnt mixture but no engine damage that I'm aware of. I jet all my 2 strokes slightly rich as I'm not running around a track all day with people to rebuild my engine when I finish

Know what an air/oil separator is? Used to get oil out of compressed air when you need good clean, dry air.

A two stroke engine works almost just like an air/oil separator. When the intake charge is drawn in through the reeds, the oil falls out of suspension in the air & falls into the bottom of the crankcase, where it is used to lube the bottom end. Ever pull the top end off, look down in the crank & actually see a puddle of oil in the bottom? The crank slings this oil around to lube the cylinder walls

jwhking1315 wrote:Know what an air/oil separator is? Used to get oil out of compressed air when you need good clean, dry air.

A two stroke engine works almost just like an air/oil separator. When the intake charge is drawn in through the reeds, the oil falls out of suspension in the air & falls into the bottom of the crankcase, where it is used to lube the bottom end. Ever pull the top end off, look down in the crank & actually see a puddle of oil in the bottom? The crank slings this oil around to lube the cylinder walls

Man. That's juicy. If so, it seems like everything I have ever been taught about 2-stroke mixture, etc is all for naught. I'm not discounting that of course -- My forefathers were legit tards.

But doesn't that just mean I can squirt lottsa lube on the crank and all is well? That goes against almost anything I have read/tried.

If that were true after two tanks of fuel you'd have around 16 ounces of oil in you're bottom end the oil stays mixed the act of the mixture moving through the bottom and top end is what lubricates you're rotating assembly.

I would think that the pool of oil in the bottom end is more of a result of evaporation of the gas then separation of the oil.

Exactly right. The bulk of oil is not separated from the fuel, but some of it is, and that residual oil is necessary for proper lubrication.

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When you think about it. Two stroke engines are more complex than 4 strokes. But the former has less parts.

The oil in the bottom end is whipped up in a mist while the bike is running. It gets "refreshed" constantly, as some does go out the exhaust due to the fact that it is whipped up in a mist

Julien D wrote:Exactly right. The bulk of oil is not separated from the fuel, but some of it is, and that residual oil is necessary for proper lubrication.

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I missed this post, but yes, a much better explanation than I've been trying to get out

2 stroke engines are more complex to understand but very simple in operation