40:1 instead 32:1

[asand1]

Originally Posted By: The_Eric
You could get away with leaning the oil mix on some of the old 2 strokes that were originally made to run on SAE 30 engine oil, but on any modern or semi modern engine, I'd stick with their recommended ratio- or at least really close.


This is backwards. Old 30wt two strokes had bushed conrods rather than needle bearings, and bare aluminum cylinders rather than nickle plated. They absolutely needed 32 or even 16:1 (oil rich). a modern 2 stroke with needle/ball bearings and chrome cylinder will run up to 50:1 (oil lean). I would mix at 40:1 personally.

Oil rich and A/F are two different things. I don't think it makes as much difference as people think.

 

[wag123]

Originally Posted By: Shannow

So every 32 pints of fuel, I have to drain a pint of oil out of the muffler ?
I've never experienced that.

Did you ever see the blue smoke coming out of a 2-cycle engine's exhaust? Do you know what that blue smoke is? It is hot unburnt oil vapor. Take a piece of clean white paper and hold it in front of the exhaust pipe/outlet for a few seconds. What you will see on the paper will answer your question about where the oil is going.
Modern high ratio 2-cycle engine oil is not all oil. It also contains a variety of additives to accomplish a number of specific goals. Some 2-cycle oils contain as much as 50% additive content. Much of the additive content DOES burn off during the combustion process, as it is designed to do. But, the oil itself STAYS oil, as IT is designed to do. The oil itself is simply not volatile enough to actually ignite in a low compression engine. You would need a higher-than-diesel compression ratio to ignite it.

 

[wag123]

Originally Posted By: doitmyself
Is this an "oil thing" or an equipment design thing?

Both.

 

[Shannow]

Originally Posted By: wag123
The oil itself is simply not volatile enough to actually ignite in a low compression engine. You would need a higher-than-diesel compression ratio to ignite it.


Rubbish...if it is in a combustion chamber with a flame going on it WILL burn along with the fuel charge.

 

[Mike72]

The oil itself is simply not volatile enough to actually ignite in a low compression engine. You would need a higher-than-diesel compression ratio to ignite it.


Rubbish...if it is in a combustion chamber with a flame going on it WILL burn along with the fuel charge.


You're both right. By itself the oil will not burn in the combustion chamber or a two stroke unless it gets heated by really high compression.

And: The oil in the combustion chamber of a two stroke is not alone and will burn with the gasoline.

 

[Mike72]

Originally Posted By: asand1
Originally Posted By: The_Eric
You could get away with leaning the oil mix on some of the old 2 strokes that were originally made to run on SAE 30 engine oil, but on any modern or semi modern engine, I'd stick with their recommended ratio- or at least really close.


This is backwards. Old 30wt two strokes had bushed conrods rather than needle bearings, and bare aluminum cylinders rather than nickle plated. They absolutely needed 32 or even 16:1 (oil rich). a modern 2 stroke with needle/ball bearings and chrome cylinder will run up to 50:1 (oil lean). I would mix at 40:1 personally.

Oil rich and A/F are two different things. I don't think it makes as much difference as people think.



Older (16:1 30wt engine oil) two strokes with bushings do require more oil for adequate lubrication, exactly how much oil they required using modern (32:1 and up) two stroke oil is hard to pin down. Modern two stroke oil does contain different amounts of solvents and additives that are not really oil. Personally I think you could use a higher oil ratio on the older (bushed) two strokes if you use modern oil, but I think it's anyone's guess as to how high you could go without risking engine damage. Modern two stroke engines use needle bearings and needle bearings require very little oil which is one of the reasons for the higher ratios used today.

 

[IndyIan]

Originally Posted By: Shannow
Originally Posted By: wag123
The oil itself is simply not volatile enough to actually ignite in a low compression engine. You would need a higher-than-diesel compression ratio to ignite it.


Rubbish...if it is in a combustion chamber with a flame going on it WILL burn along with the fuel charge.

Well, you can get cool enough combustion that not all of the 2 stroke oil is burned. When I was 15 I bought a used dirt bike from a dealer and was told to to run it 20:1... So I did, and there was some oil spattering on the back fender out of the exhaust. It was air cooled and I had to burn the carbon out of the expansion chamber every year or two, but then I also ran hundreds and hundreds of hours without re-ringing it either. Not the greatest idea, but I didn't know any better at the time.