2 stroke lubrication vs. jetting and fuel properties

[motometal]

thinking about this, let me know your thoughts please (am I right?)

the lower end of a two stroke is lubricated with the oil left behind when the fuel in the premix vaporizes. Pure oil is a better lubricant than oil diluted with fuel. So, wouldn't the following be true?

1. Leaner jetting supports better lubrication because a greater portion of the fuel charge is likely to fully vaporize.

2. Fuels that vaporize more readilly and completely support better lubrication for the same reason.

3. All else being equal, an engine operating at a higher temperature will tend to have more effective lubrication due to a greater portion of the fuel charge vaporizing.

???

 

[MikeS]

1 . Just not way lean since if you starve the fuel...you starve the volume of oil.

2. Yes

3. see 2.

 

[Radiator Ron]

If you lean it out too much you'll overheat the combustion chamber and damage the engine. You need proper air/fuel mixture to cool the combustion process, this is the only thing you need to worry about when jetting your carb. If you want more oil add it to the gas. The higher oil content the better lubrication you have the biggest hp gain in oil ratios is between 40:1& 32:1. Oil actually seals the rings, helps blowby, and increases power. Most bikes are at 32:1. 20:1 is better yet but it starts to foul plugs. Another thing is some smaller bikes that turn high rpms (ie 14000) sometimes have less oil specs (ie 40:1) due to too much oil on rod bearing will actually overheat it and cause bearing failure. Bottom line run what the manufacturers call for, if its jetted right you wont foul plugs, or wear things out prematurely.

 

[Jaybird]

Ron,
You'll find that HP increases can be found with even more oil than 20:1...and if you are jetted up for less oil, then I garantee you won't start fouling plugs going to more oil, Quite the opposite. I'd be intersted in knowing more about the "too much oil on the rod bearing" thing. Fill me in a little more.

Scott....
You have brought up a very intertesting thought.
Conventional 2 cycle oil does fall out of suspension from the fuel and the residual protects the mechanical parts by creating a film layer that protects from friction.
However, there are some technologies of late that utilize a chemical process that can protect the parts without totally relying on the film layer. This technology actually co-mingles with the oxide layer of the metal surfaces which creates a friction barrier, rather than relying soley on conventional film thickness for protection. Utilizing this method can allow you to depend less on proper fuel atomization to have good lubrication.

But yes, I think that whatever type of oil or additives you use, a more completely vaporized fuel is going to be more efficient in both combustion and lubrication.

 

[Radiator Ron]

Jaybird, I only used 20:1 as a reference, i understand theoretically more oil = hp. The biggest hp gain/loss is the 32:1/40:1 range though. Now back to carb, the first step in 2-stroke jetting is picking your oil ratio. I would say to stay at manuf recommendation, but run what you want, everone has thier own preference. For longetivity of engines and ease of jetting I prefer 32:1. Once you choose oil/fuel ratio stay with or it can effect carb jetting. Now that you have lets say jetted your fuel mixture, you have to get the proper fuel mixture/air ratio through the carb. X amount of your fuel mixture will flow through a lets say a 100 main jet. If you use 32:1 you will have more gas and less oil than 16:1 which would be less gas and more oil than 32:1. Therefore if a bike is properly jetted at 32:1 with a 100 main, and you switch to 16:1 you will lean the bike out, so you may need to increase main jet to lets say 105 to have bike properly jetted again. The end result from going 32:1 to 16:1 is you may need to increase main get to get proper air/fuel ratio to cool combustion, but you will have more oil in the engine. The carb atomizes the fuel mixture and is carried to the crankcase where engine heat vaporizes the mixture which allows the oil to fall out and do it's job of lubrication. So to answer motometal you need heat to vapoize fuel, but once you have enough heat to do that you dont need no more, raising the temp would only lead to possible overheating of the engine and poor performance. I dont want to write about the fuel faster vaporizing, but your right a faster vaporizing fuel could tend to lead to better lubrcation but i cant see where this would be an issue with any current fuel. Now all the oil we have put into this engine will go through the engine if we put too much oil in engine it will not be properly burned so we get the spoog everyone talks about, plus it will tend to lead to a fouled plug. So to burn the oil you would cut back on the main jet which would decrease our fuel mixture letting less oil and gas through carb. Less gas would elevate combustion temp, helping to burn oil and since theres less oil it can be burned better. Get that? Now if we use 16:1 instead of 32:1 this is what will happen. We have more oil in gas, this will take away from fuel to air ratio because the fuel mixture has to go through the main jet, so to get the proper fuel to air ratio to cool combustion we increase main jet, which allows more fuel and oil to enter engine. But wait now we have more oil that will need to be burned. The problem here is if we decrease the jet size to burn oil we could overheat the combustion chamber, and if we stay where we are we might not be able to burn oil and can foul plugs. Some bikes can run there fine at high rpm but it's the low rpm that gets you. thats where good carb tuning comes into play. Main jet is set for wot only. These bikes are made to run not idle, so at 16:1 wot your bike may fine, but now you go into woods you dont have heat to burn oil so bikes start to load up. you can try smaller pilot jets, or larger diameter needles help with this but there again you have to be able to burn oil or here comes the spooge and a fouled plug. So it may be better to tune and engine with 32:1 not so much for wot but for low rpms because you will need to burn less oil to keep from fouling plugs. Thats why the first thing people do is cut back on oil like 40:1 because you have less oil to burn and it seems to help thier situation. Where if they had jetted the bike properly by using main, needle, pilot, mixture it would've made the bike run better to begin with and still gave better lubrication & hp. Now jay bird and that rod thing alot of the very high rpm engines can create heat that can be aggrevated by excess oil. Some of the smaa engines turn 14000+ rpms almost twice as fast as a 250. Smaller engines use smaller parts spin faster so friction and oil temps can become sort of an issue, they are kind of on the edge in a sense more so than a 125 or 250. Too much oil can actually add to the friction the bearing has to overcome to rotate freely and also retain heat in the bearing. That said if you take all the factors a small engine has to endure adding friction to a bearing can spell disaster. Most high speed 2-strokes recommend 40 or 50:1 but yet turn much greater rpm tan a 250. Another aspect of this friction factor is you have a 125 and 250, you run both 32:1 and put the same hrs on both, the 125 would have greater internal wear because of higer rpm causing more friction. Bottom line manufacturers are'nt asking us to run a crazy ratio of 100:1 so we blow engines up. They recommend a ratio they believe will satisfy the engine in the operating range and limits it was designed for.

 

[Jaybird]

You'll have to do better than that to convince me that more oil on the bearing suface creates more friction that the part can overcome.

If we were talking about a sealed bearing using grease for the lubricant, then I would agree that a bearing casing with more than 60% fill can begin to create forces that work against optimum performance, but not on a oil coated, open bearing.

Re-read what you said about the jetting and ratios and see if you haven't gone around a confusing circle. Try to state things assuming that we are jetted properly in ALL circuits for the riding we do.

 

[kdxtodd]

Jaybird, Ive been using that new technology oil you speak of, blue marble. By using the oil are you saying that I would pay less atention to jetting because of the way it lubricates?

 

[Radiator Ron]

jaybird heres a little take from sensormag.com they deal with monitoring bearings in gas turbine engines. Gas turbines usually use ball and roller bearings, in a dry sump. " Each bearing in an engine receives oil from a metered or calibrated orifice. This is important because too much oil would cause the bearings to skid, resulting in high friction heat, and in a relatively short period of time , bearing spalling." Now like i said gas turbines use a dry sump so theres no puddle of oil in sump, and they use the most sophisticated syn oils. If this still is'nt good go to www.lubes-n-filters.com then to newsletter archives, then to bearing basics. they will also tell you and open bearing with too much oil will overheat. By the way that's an amsoil site so they should know what there talking about right. I searched these this afternoon first time at these sites, guess ymc was right in stating small high rpm engines can overheat bearings with too high oil/fuel mix. Thats all i will state on excess oil its the fact.

 

[Jaybird]

Todd,
I'm not very familiar with the Blue Marble product. I can only assume that they are using a similar technology to our products. What our new product does is actually co-mingel with the molecular oxide layer of the metals surfaces, which creates a load carrying barrier that is superior to the conventional film layer that conventional oils depend upon. Our product is actually an additive that can be used with any petroleum oil, both in the cumbustion process and gear protection.
Using this type of product will not let you pay less attention to your jetting. Proper carburation is essential to performance tuning. What this technology will do is allow you to use less oil, while enjoying a better load carrying property.

Ron,
I hate to sound argumentative.....wait... no I don't. :)
Read your materials a bit closer and you will see that what I stated before will be confirmed in the documents you cited. You will also begin to see where your flaw is.

You will never see too much oil in an open bearing situation. What you are reffering to happens in closed bearing and bath situations.

It is refreshing to see others start to understand a little bit about tribology though. Or at least take an interest.

On reflection....Ron, when the fuel in a fuel/oil mix does not completely vaporise prior to cumbustion, the wet fuel can actually wash off the oil from the bearings....perhaps this is what has you confused.

 

[motometal]

"On reflection....Ron, when the fuel in a fuel/oil mix does not completely vaporise prior to cumbustion, the wet fuel can actually wash off the oil from the bearings....perhaps this is what has you confused."

this is the type of thing i'm trying to start discussion on.

Ron, I applaud your efforts on the long post but please hit the return key a few times in there and make some paragraphs! Otherwise, my feeble brain can't handle that many words in a row without a break!

 

[Jaybird]

Some fuels are desinged for use with intake tracts that are quite a bit longer than what a bike will have. They tend to not vaporize completely after leaving our carbs, however the same fuel will be well suited for a quad holley with a highrise edelbrok intake.
I just wish I understood enough about distillation curves to be able to know what fuel is proper for what. :)

 

[motometal]

the Sunoco i'm currently using is probably in this category, but withing limits that's not all bad. The plus side is that the components of the fuel that are not vaporizing until the late stages will help keep things cool.

 

[KX02]

motometal, the carburetor vaporizes the gas AND oil. That's what carburetors do. A properly jetted and carbureted engine does not "leave oil behind". It rides along with the gas, also lubes the cylinder walls, rings, top end bearing, power valve and lastly, the muffler packing LOL!

 

[Jaybird]

If all the oil remained in a gaseous state, how would it lubricate anything?
I'm fairly certain that some of the oil has to condensate and return to a liquid state.
Or perhaps it never fully vaporized?

I'd love to hear Rich or another tuner chime in here.

 

[KX02]

The oil doesn't turn into a gas. The fuel and oil get's finely distributed into the air passing through the carb. As this mixture passes through the engine and meets all the metal surfaces some of the mixture sticks to the surfaces and falls out of suspension.

 

[motometal]

I don't think the oil completely vaporizes. I think it's in droplet form as it's carried through the engine, at least until it reaches a higher temperature. The lower pressure created by the engine could encourage the oil to vaporize at a lower temperature (all else being equal), but this isn't a static condition.

Look at the distillation curve for your favorite fuel, then compare that to the curve for your favorite premix oil.

Consider water squirting through the carburetor. With the carb and the water at room temperature, I think at least some of the water would remain in a droplet form as it was sucked into the intake tract. Now replace that water with oil, which vaporizes at a much higher temperature.

 

[nephron]

By the way that's an amsoil site so they should know what there talking about right.

...same flakey door-to-door company that recommends that 100:1 ratio you mentioned. Remember that they heavily rely on the 3 ball wear test to push their dope, and if your reference to the rollerball/case bearings and oil content is correct, then Amsoil's oil would overheat those motors like a dragster in traffic. :eek:

By the way, from what i understand, the only thing that determines film thickness on a rod bearing, eg, is bearing clearance. Hence the need for proper bearing clearance.

 

[Jaybird]

He is correct though, they SHOULD know what they are talking about. (grin)

KX, so atomized rather than vaporized, aye?

 

[kdxtodd]

From what ive read about blue marble, its supposed to change the metal structure to more of a ceramic type suface through a chemical reaction. They say they have a patent on it but your oil additive my do it differently, don't know. Although I do use way less oil, about 60-70:1 and have more power, almost no carbon build up, and get better fuel economy.

 

[nephron]

For obvious reasons, oils are more difficult to "boil" or "vaporize" than fuel. Think about the process of separating fuel components from crude before hydrocracking (and whatever other methods they're using now)...hey, surprise, surprise...the initial process is distillation.

Take that fact, and think about microdroplet of premix. As ya get traveling closer and closer to the combustion process, things are getting hotter. The 10% points of these race fuels now are around 110-150 Fahrenheit, and the fuel's obviously going to vaporize RAPIDLY leaving a higher and higher fraction of that droplet as oil. This leads me to believe that both theories are true: There's probably some droplet lubrication at startup and the cooler areas, while the majority of lubrication seemingly has to occur by leaving the oil behind.

For reference, brake fluid boiling points (an important issue) are 300 to 500. Think what premix is. I'd bet there's NO oil vaporization occuring until combustion (the small amount that makes it that far).

Of course, I wouldn't be surprised to find out I'm totally full of s**t. :laugh:

 

[motometal]

I think you are right, Nephron.

remember folks, premix is a mixture of oil and fuel. Actually, and oil and fuel themselves are mixtures of other components as well. The oil within the premix should still vaporize at the same temp that it would by itself.

Think of cooking a nice batch of speghetti, and adding some red wine as you are cooking the sauce at 200 F. Try it some time, once the wine gets hot the fumes from the alcohol will just about knock you out. The alcohol vaporizes and floats away, while the rest of the components in the wine stay behind. The wine is a mixture of alcohol, water, and other components.

From a chemistry standpoint, I think i'm on the right track here. Question though; if we have a mixture of anti freeze and water, why don't the individual water molecules freeze at 32 F?

 

[nephron]

Each ethylene glycol molecule is more intimately associated with water molecules (don't know the stoichiometry), is my guess since that same concept is true with NaCl.

 

[ML536]

Wouldn't either the ethylene glycol or the NaCl interfere with hydrogen bonding? And wouldn't that cause the water to freeze at a lower temperature?

 

[motometal]

as I walked away from the computer after posting that, I asked my wife and she said what Nephron said.

I still think the oil and fuel in premix maintain at least some of their original properties.

that hydrogen bonding thing sounds interesting but it's over my head. please explain more.

 

[Jaybird]

I think the soluability of the additive is where the secret is in both anti-freeze mix and oil/fuel mix.
I'm fuzzy on the oil/fuel part still...but on water that has a solute added, (like eth. glycol or NaCl for that matter) it both raises the vapor pressure allowing it to remain in liquid form( or making it harder to go to vapor), and decreases the amount of H2O molecules allowing it to have a reduced freezing point.

I suspect that the oil/fuel mixture is much less soluable than water/glyc. which is probably the way we want it so the fuel will vaporize easily leaving a considerable amount of oil behind.

I may be way off here....