oil migration

[DGardner]

Here's some good info on oil migration.

[DGardner]

sorry it's hard to read but find it on line and read it.....I think it will shock you on how fast or slow oil can migrate through a engine.

[dcooke007]

This is the link to the oil migration chart. Makes interesting reading.
Danny
http://www.maximausa.com/pdf/Oil%20Migr ... 0Sheet.pdf

[ossa95d]

It is very interesting reading and seems to support discussions we have had in the past.

[hodakamax]

Hmmm, maybe, migrating from where? Any place receiving fuel is receiving lubrication. I'm always skeptical on advertising claims. Lotsa questions on this report. I'm not a total skeptic but I'll need a lot more info to buy into this one. Just being the devils advocate!

Max

[dcooke007]

Max,
I am working on an engine now that seized and I think may lend some credibility to this info. Pictures and my thoughts to come later.

Danny

[hodakamax]

Still thinking on this one. Fuel mix is probably a solution rather than a suspended emulsion. Oil dissolves or is thinned by lighter fuels. How much fuel evaporates into a vapor is the question. Some is probably the answer. How much, not determined. Fuel is atomized in the carb (with its oil in solution.) It's hard to imagine that oil is separated somehow after the atomization of the fuel mixture. It appears (to me) that fuel/oil mix is sprayed throughout the engine with very little evaporation of the lighter volatiles. I don't see a separation of the oil/fuel mix in such a short period of time. Everything should be lubricated by the fuel/oil mix. Lack of lubrication is a function of jetting and fuel/oil mixture. If it's lacking lubrication at high RPMs it needs a bigger main or more oil. I don't see separated oil migrating around the engine. Why would the oil stop and start migrating, one would think it would still be in the flow. Just thinking out loud.

Max

PS--Hey, just trying to keep everyone thinking.

[dcooke007]

Hey Max,
I think oil is heavier than fuel and also does not atomize as fuel does. My thoughts are oil will drop out of the mix at lower rpms in the crank case area. To me, at higher rpm's and related increased pumping action the engine moves more oil through the engine. At extreme racing rpm's I think there may not be enough time to replenish and maintain the required oil film at high ratio mixes. This may be a moot point to the average trail rider but could be a serious concern to the guy that runs the engine flat out for an extended period of time like my friend Will / Tired Combat Wombat. I had read a report where radioactive isotopes were added to two stroke oil and with the aid of a geiger counter oil migration was measured. It seemed to confirm what the Maxima chart indicates.

Danny

[Bullfrog]

Like Max, I have a bit of trouble truly understanding what the document says. Example: What is "Oil Migration Elapsed Time Thru Entire Engine"? I have several guesses regarding exactly what that means . . . but they are all guesses. And, what is "Oil Migration Dwell Times"? Again, I have several guesses as to exactly what that is.

However, the recommendation seems pretty clear. Maxima feels that if you spend higher and higher percentages of time operating at full throttle, you should have more oil in your fuel mix. Hard to argue with that.

And it appears that Max agrees - " Everything should be lubricated by the fuel/oil mix. Lack of lubrication is a function of jetting and fuel/oil mixture. If it's lacking lubrication at high RPMs it needs a bigger main or more oil."

The particular state-of-tune of the 125cc engines I rode in the 1970's and that I ride now - enduro style power bands . . . AND my particular riding style (decidedly NOT full throttle all the time, both then and now ) has allowed extremely good engine reliability with 40:1 and 32:1 pre-mix ratios.

Ed

[hodakamax]

This is fun! I really like these kinds of discussions on the Forum. It's rather like a puzzle with clues. I think our problem on this one is that we don't have enough information on how the test was conducted or what they were measuring where and what for..(If that makes sense). We've discussed this one before on the Forum and it seems we had more information last time.

Back to the subject. At low RPM riding and idling you are not doing much work and generating little heat. At high RPMs you are producing more power AND heat. The lubricating part of the mixture may failing due to heat and require more oil to the mix to lube properly. Maybe--at least a factor.

Maybe migrating is being confused with how wet the lubricated part is. I don't see the oil coming out of the mix to lubricate the part. I see a spray of mix wetting parts. Am I boring you?

All good for the brain.

For now,

Maxie

[ossa95d]

Danny,
I read the same report about adding radioactive isotopes to the oil to measure the amount of oil at the exhaust exit. My recollection was that at idle nearly all of the oil remained in the engine and the oil accumulated as pooling in the lower end and a film in other points, and at sustained maximum throttle and rpm's nearly all of the incoming oil was accounted for at the exhaust. This would explain why when you open the throttle after a long period of idling there is a lot of smoke from the accumulated oil being cleared out. There are many oil injection systems that add no oil at idle because tests have shown that the residual oil film is sufficient for lubrication at idle to sustain the engine for up to 30 minutes with virtually no migration from the system. It appears that at maximum rpm the oil migrates out nearly as quickly as it is introduced. I was not involved in this testing but it seems plausible.

[DGardner]

I think if you look at the gravity of gasoline and oil it will show you how the two would separate as it inters the crank case. This is just a guess but I would say the gravity of gasoline is around 73-76 and the gravity on the oil would be around 35-40. So the gasoline weight is less than the oil. If you look at a distillation of a gasoline you will see that the end point is around 350 deg. So at 350 Deg. all of the gasoline is vaporized into a gas. If you do the same to the oil the end point would be around 750 Deg. The gasoline and oil inter the carb and get atomized and mixed with air, then inter the crank case that is around 200-250 deg. the gasoline is now a gas (vapor) and mixed with the air. The oil that has a lot lower gravity (heavy) and higher end point will separate from the gas air mix. Now the gas air mix can do it's job of making power in the combustion camber and the oil can do it's job of lubing the engine. I hope you can see what I'm trying to say.

So set your oil gasoline mix for what kind of riding you will be doing, trail riding 32/1 is a great mix to use. If you are riding on the road and hold the throttle wide open with a high rpm you would be better off with 20-24/1. Now that you have set your oil/gasoline mix you can jet your bike for the gas/air mix with the jets in your carb.

The other thing that you need to look at is what kind of oil you use. What was the oil made for, water cooled or air cooled. If you look at some of the specs on modern oil you will see that it is made of a lighter weight oil and the flash point is a lot lower than a oil that was made for a air cooled engine. If you use some of the newer oils in a air cooled engine that is ran at a very high temp for longer times the oil will flash off into a vapor and you have now lost all your lube. You will see this happen on the exhaust side of your piston first.

[hodakamax]

At least at the upper RPMs the mixture is never going to reach 350 degrees except in the later stages of compression. Atomization and evaporation have a huge cooling effect. At idle maybe the volatiles are cooking off leaving oil lingering but at least one other factor would come into play which is saturation of the air with fuel much like rain when the humidity reaches 100%. All the gasoline couldn't become a gas because of this effect. Also, if that much liquid is turned into a gas pressures would increase substantially in the crankcase which I'm not seeing. Another complication is the pressures fluctuating from intake vacuum to crankcase compression prior to transfer which changes the temperature at which a liquid becomes a gas drastically. In near vacuum gasoline could boil at room temperature or at high pressures never become a gas. Complicated huh.

These are not necessarily facts but only observations and thinking out loud. It would be interesting to measure the temperatures of the mix as it enters the cylinder at different loads and RPMs. I would think it would be cold at higher RPMs and in the form of liquid droplets rather than a gas. The compression in the crankcase could heat the mix as the piston comes down to compress it. Hmm, lotsa factors at work here.

Max

PS--Of course discussion is fun but rarely proves anything--We need a real test with real engines and no bias.

[dcooke007]

Hey Max,
Very interesting stuff and I can report my old 120 horse 4 cylinder 2 stroke boat motor has demonstrated frost on the reed manifolds after long wide open runs. I attribute the frost/metal cooling to atomization / evaporation of the fuel mix. Being an older 1989 vintage pre-mix is used in this engine.

Regardless of all the physics going on in the engine there are 2 strokes that have recirculating systems to scavenge excess oil from the crankcase. My old 2 stroke boat engine is one of them. I also have a 1974 750 Kawasaki H2 and it is equipped with three check valve assemblies that are designed to recirculate excess 2 stroke oil from the crankcase. To be honest the H2 is oil injected. I am sure there are other examples and this to me is a really good example that 2 stroke oil can drop out of solution at lower rpm's.

My internet connection is not very good at my present location. I have some pictures I want to up load but can't at the moment. Unfortunately Will seized his engine on the first race of the season and it appears it is an oil related issue. I think it will demonstrate some of the things we are discussing at the moment. Be it oil quality or quantity.

I know this can become a passionate discussion but we can all have our opinions and still be friends.

Danny

[hodakamax]

Hey Danny and Gang, obviously some oil retention is happening, I'm just trying to think out loud. I don't think it's as simple as we are trying to make it. I don't think any of us are disagreeing, only trying to find out what the heck is really happening. All fun, got company coming, may have a new theory in the morning!

Later,

Maxie

[hodakamax]

Ok, you're going to like this in that Max has changed his mind on this subject but not totally. Here's my new idea on what's happening. Air is rushing through the venturi being drawn in by the pump function of the engine. Fuel is coming in and being atomized creating MUCH more surface area for fuel to evaporate. Also the flow is being subjected to a low pressure area caused by the intake vacuum which increases the evaporation rate. Evaporation is happening at a high rate and we can tell by the extreme drop in temperature which is a function of evaporation. Volatiles evaporate first leaving excess oil. Some of the fuel has turned into a gaseous form but is limited by the air becoming saturated by fuel. In an idling situation oil droplets probably do start to build in the crankcase. All of the fuel has not evaporated due to the saturated air. The fuel has not turned into a gas from heat but from an increase in surface area and low pressures.
The saturation point is also a function of pressure. A near vacuum of intake causes the fuel to evaporate at a higher rate but as the crankcase starts to pressurize from the descending piston the rate of evaporation drastically decreases and may even begin to precipitate back out. At low RPMs oil probably does accumulate in the crankcase. As RPMs increase air flow begins to push residual oil from the crankcase. At high RPMs a high speed flow doesn't allow oil to accumulate and it may well migrate from the crankcase but everything is still well lubricated by the droplets with an increase in oil proportions in the droplets (if you've mixed the proper amount of oil).

I guess I'm always thinking of high speed performance where this would not be a factor. At high RPMs we would jet and mix oil for the requirements of a race engine. Residual oil would only become a problem in a race engine that was operated at lower RPMs (in that it could foul plugs).
So kinda summarizing, residual oil would only be an effect of a low speed engine really not affecting proper lubrication. This means that we don't have to wait for oil to migrate, we have the proper chosen mix.

Defending my opinion when it's wrong would be silly and I did learn something as we all should every day.

Max

PS--I guess that I should also mention that when the engine is shut down most of the volatiles evaporate leaving the oil to settle into the crankcase.

[ossa95d]

Max (not to be confused with Maxima) continues to raise the question of whether oil migration is an important concern for engine lubrication. Maxima (not to be confused with Max) seems to suggest that it is but a lot more information would be required to understand the full implications. It would be interesting to see how they arrived at their migration numbers. I think we all agree that the common ground in all of this is that small displacement high rpm race engines need more oil in the premix than a large displacement low rpm engine. The Maxima chart looks like a reasonable guide for oil premix ratios. Good discussion!

[DGardner]

What got me interested in all this gas oil mix and what kind of oil will work best in a air cooled engine was this goal that I have of riding a iron butt (1000 in 24 hours) on a 72 wombat. Last year was nothing but problems with the bike, running 927 maxima with the older dykes ring the ring would stick in the ring landing on the piston, running a modern synthetic with the same piston I stuck the piston and all this was done with a 24/1 gas oil mix. When I pulled the motor down each time I found that with the 927 there was a lot of oil in the crank case and on the liner and piston, with the synthetic oil it was dry as a bone. Now how can that be? What I think is that the newer synthetic oil was made for a water cooled engine and is made of a lighter base stock. This would lower the flash point on the oil to where if the engine got to hot the oil just flashed off and you would stick the piston. I work in a oil refinery and would like to send some two stroke oil to our lab and have them run a distillation and flash on them just to see what the difference is in some of the newer oils to a oil that is made for a air cooled engine. This year I've been running a oil that was made for a air cooled, high rpm, high heat engine, it is made with a synthetic, petroleum, castor mix with only 10% of it being castor. I will give some feedback on how good it is later in the year.

[ossa95d]

Not all 2-stroke oils are created equal. Oils that were developed for a high rpm air cooled engine had the API-TC rating listed on the bottle. Most 2-stroke oils available today meet a TC-WII or TC-W3 rating. The "W" in these ratings stands for water cooled and they are formulated very differently from an oil that is designed for an air cooled engine as the requirements of the two different engines are very different. Many modern oils probably would meet the API-TC rating but the manufacturers may not want to go through the very stringent and expensive requirements to meet the standard. I always look for an oil that lists API-TC on the bottle such as Maxima Premium II. Caster based or blended oils like Maxima 927 work well with air cooled 2-strokes but are much more dirty than a synthetic. I'm sure there are many more, but I would stay away from outboard motor oil for an air cooled high performance engine.

[dcooke007]

Ok, back home now and below are pictures from Will's bike. Spark plug photos will be in next post.

Will's engine has seized twice since built and raced.
1. Piston crown on the left is the first seizure and occurred last year. Seizure occurred during extended high rpm operation while cross country racing.
2. After first seizure, piston on the right was installed and a different head was installed to reduce cranking compression. Bike was raced successfully several times last year with the second piston and seized the first race this year. This seizure also occurred during extended high rpm operation...but at a vintage motocross race.

If you are going to have a piston seize this was the best way to have one for diagnostic purposes. Although the seizure occurred over a short period of time, Will reports engine operation ceased almost immediately. He coasted off to the side and was towed back to the pits. After a minute or so the engine would rotate when slowly kicked over. Will did not attempt to restart the engine. When the bike arrived at my house I removed the spark plug and did the thumb over spark plug hole compression test....passed thumb test and the ring was not stuck. Piston skirt is moly coated and crown coated also.

Exhaust side view of second seized piston.

Intake side view of second seized piston. Scoring is on the opposite side of the exhaust scoring.

Under side view of second seized piston.

When I say high rpm operation...that means Will had the throttle pegged and the engine was wound out as fast as it would go...and for a longer period of time than most would be comfortable with. In races with more moderate requirements the engine performed with out failure.

Of course the cylinder had matching piston material attached to the bore. Fortunately the cylinder was plated by Powerseal and a little diluted muratic acid removed the piston material. There was one small nick in the plating but nothing that requires attention.

Also, there was a good coating of two stroke oil on the rod and small end bearing. The intake side of the piston and cylinder had a reasonable amount of two stroke oil but the exhaust side of both was lacking.

At this point I am going to let you guys examine the photos and comment.

Danny

[dcooke007]

Not easy to photo but in the last pic you can make out the soot ring at the base of the insulator.
Danny

[Bullfrog]

Insulator color is too light for my taste. And I developed a taste for darker brown coloring on the insulator as a result of a real dislike for seizures. So my $.02 is -- slightly lean on main jet.

Ed

[dcooke007]

Ed,
I too would like to see a little more color on the insulator. However, the crown of the piston has good color on it and no damage. I think there is a little more going on here.

Danny

[Kels]

Without seeing more of the piston.. I would say that you have too tight of an exhaust stinger.. or a silencer that is restricted.

Also shows a little sign of an slight over-heat...

I would also run 20:1 on the oil... What oil ratio were you running?

The oil migration topic is interesting.. there are SAE papers to support what Maxima showed..

[taber hodaka]

Good oil bad oil. If there were castor based oils that work well with air cooled 2 stroke engines I have never used one I had my fill of them back in the 60's. I have never tuned a motorcycle by changing the oil mix ratio. I have had to increase jetting when using a poorer grade of oil. The study would be more interesting if it had been run with a variety of oils. The old oils I used in the 70s and still use today has a flash point of 380 F. Use what the winners are using?? Some oils mix much better with gas than others. --------------Clarence