oil migration

[dcooke007]

Hey Kels,
Yep, pictures are not as good as seeing the parts in person. The only place the piston shows any excess heat is in the area of scoring and the oil film flashed off the small oval area inside the piston. The oval area pictured is the inside of the seizure on the exhaust skirt. There is a coating of two stroke oil on the balance of the inside of the piston.

Oil ratio and possibly brand are starting to key into where I am thinking the root cause of the problem may exist. Will is using 32/1 ratio and Repsol oil. It may have some good uses but I am not sure this is one of them. Will wanted to run the same oil and ratio for the sake of simplicity with his other bikes. His other bikes are larger displacement and live just fine on this mix.

I had not thought about the exhaust stinger. It has the stock combat wombat exhaust with the stock early spark arrestor. I did check and it is not blocked or carboned up. It is however not the most free flowing. With the lack of excess heat in the rest of the piston I have to wonder if that is a concern.

Danny

[taber hodaka]

Danny what oil were you using and what ratio? For street riding I liked a chocolate brown but for racing I go for black but not wet. To me it looks too lean or low quality oil. ------Clarence

[Bullfrog]

I'll wait for your final results. (Um haven't heard any strong defense of the main jet selection which provided that light tan color. )

Ed

[hodakamax]

I think we sometimes over-analyze a somewhat obvious situation. After reading about the conditions (wide open, high RPMs for an extended period of time) and seeing the plug and piston pictures it was (as Bill Chapman always says), "Too lean for the conditions". I always summarize with "It got too hot". Not only does the mixture lubricate but it cools the engine. Wide open--all lubrication and cooling fuel is coming through the main jet which in this case is too small "for the conditions". Worse yet, when it gets too hot the lubricant then fails. It's all down hill from there as we say.

The plug shows too lean. The bike ran good during the season but was never ran past that limit. Everyone has heard Max's lecture before, but I see no mystery here.

OK, I'm old and set in my ways and when you ask for an opinion I always have one. If you are a Hodaka Club member (which you should be) you can read more about piston seizure in The Resonator, vol. 2, no. 17.

Maxie

PS--I guess I should mention that there's about a 5% chance that it's that other list which includes timing, bad fuel, wrong clearances, air leak etc. but I seriously doubt it.

[Kels]

Here is something that is going to spark some controversy regarding what information you can "source" from a plug color color reading using a modern oil.

The old days of "color" telling you much information lost a lot of validity when oils took an advance in technology.

In short.. plug color basically tells you the color your oil burns and not very much more. Basing your jetting on the color of the plug will usually lead you to improper jetting IF you are using a modern oil..

On Danny's engine, I would still bet on the restrictive exhaust outlet.

[dcooke007]

The question of whether the piston was over heated / to hot is the million dollar question and from what cause. From my observation of the piston and piston crown, the piston, as a whole, does not appear to be over heated. Except in the area where the scoring occurred and the small oval area inside the piston on the exhaust skirt side. It looks more like the oil film flashed off / failed, metal to metal contact, scoring and then engine seizure. Obviously the scored areas over heated....but it appears to have been friction related as evidenced by a lack of heat in the rest of the piston. The oil film was pretty much non existent on the exhaust side of the piston and cylinder. If the oil film flashed off, reducing engine temps or using an oil with better lubrication is part of the solution. I agree the main jet was a little lean for the conditions, but it looks like with a better / more oil the piston would have survived. And yes a larger main jet would have provided more oil and cooler engine temps. But, can we have our cake and eat it too. If we can make more power with higher operating temps and changing oil makes the engine live????? I keep coming back to the piston crown condition. Piston crown looks like it was happily humming along until the seizure occurred. I can just imagine the piston crown saying to the skirt, "what the heck are you doing"?

There is some other useful info on Maxima's web sight. Most of the two stroke oils they sell list the flash and fire point of their oil in degrees fahrenheit.
1. 927 - Flash point 420 Fire point 480
2. K2 - 240 280
3. Bio 2t 180 not listed
4 Super M 280 300
That is a pretty large range of temps and this is just one makers example. I could not find any of these specs on Repsol's oil. I have to wonder if an oil with low flash and fire points could provide proper lubrication for this type of use.

Any way, lots of things to consider and as this engine is developed hopefully some good info can be gleaned. Proof is in the pudding as you know. My plans are to use a different oil / ratio, minor re-jetting and testing.

I am sure these kind of discussions will continue and keep us old codgers awake at night.

Danny

[hodakamax]

As for plug reading, it was secondary as a guide for jetting in our racing program ITD, (in the day). We started with a main jet (which is the one that over 95% of the fuel goes through in a race engine--near 100% on a short tracker) that was obviously too large and worked down past the 4-stroking stage. Accurate plug readings for a short tracker required a new plug and several racing minutes and shutting the engine down under race conditions while pulling in the clutch. Only then do you get an accurate reading. Otherwise you are just reading what happened all day rather under race conditions or trying to read a plug after seizure only tells what was happening at the last moments of destruction. The plug above shows lean conditions but is it because the engine is melting down? The plug is not the indicator, the melting piston is the clue that IT GOT TOO HOT!

Food for thought and one must remember that most piston seizures are caused by lean conditions causing overheating which then cooks the lubricants beyond their effectiveness. OUCH!

Max again.

PS--we've forgotten one other number to list and that would be the melting point of Aluminum at 1,221 degrees F.

[Kels]

Danny... the too tight of stinger possibility is directly related to the lack of oil on the exhaust side skirt..

When you have this condition, the heat builds on the face of the piston and the oil, if not sufficient, gets removed and this type of scoring occurs. In short, the heat cannot get out quick enough and the heat continues to build until you have a failure.. getting the heat out of the engine is critical to having an engine "live" on prolonged WOT pulls. I see this all the time with aftermarket silencers that are too restrictive...

The crown does not look over heated.. nor does the plug look excessively lean IMO..

Keep in mind, the crown wash or the plug color are NOT a "snap shot" of how the engine was running just before failure.. They are indicators of how the engine was running over a much longer period.. It is an average indicator at best.. Again.. pulling the plug is going to tell you VERY little about the tune of the engine .

[hodakamax]

We can always add one more idea that adds heat but the bottom line is that the main jet is regulating the temperature. Most of the cooling of the engine comes through the carb. The places we see melting are caused by friction of rubbing metals as the lubricants are no longer working because they have exceeded their temperature requirements. The exhaust side is where it starts because it is the hottest to begin with. When we jet "for the conditions" we are jetting for ALL of the conditions whether too small of stinger, weather or load requirements. If you're using crap oil you're going to have to jet it richer. Not only does it not lube as well (friction=heat) but it breaks down at lower temperatures. Everything that adds heat must be compensated for.

Max

Ps--Advice from not just Max but all vintage two-stroke tuners--It's THE NUMBER ONE RULE. Once I got that in my head I NEVER melted a race engine.

[dcooke007]

This is proving to get more interesting as we go. I appreciate and value every ones input. Lots of old codger brain cell work outs going on....and maybe not so old. As long as I can continue to remember what was discussed yesterday we are good to go. .

Kels,
I too have noticed a change in spark plug color over the years. No leaded gas, alcohol additives, who knows what other things have changed in the fuel we use. Not to mention modern two stroke oil formulations.

Your comments about the restricted arrestor are being taken seriously. The engine is not stock. Larger carb, converted to reed valve, modest porting and modestly greater compression. Very possible the air flow through the engine has increased past the point of arrestors capacity. I will see if some mods can be made.

Doug,
I did not intend to take over your post. Just seemed like this failure applied.

Danny

[hodakamax]

Oops, we have hijacked your post Doug, but for a good cause. I guess I'm part of the problem!

Maxie

PS--good discussion on oil migration, It made me think (and even change my mind somewhat).

[Kels]

Max...

Think about this--> You can not seize a piston unless the oil barrier breaks down.

So, in the end, ALL seizures are the result of the oil barrier breaking down.

The real area to investigate is WHY this oil barrier broke down?

As mentioned earlier, oil MUST fall out of suspension in order to do its job. It is the "basis" for the whole 2 stroke lubrication functionality.

I wrote a tech article years ago about oil.. It is pretty basic but covers some areas that pertain
http://www.2strokeheads.com/OIL-TECH.htm

You are correct that fuel is the #1 cooling agent present..(see article above).

The fuel is NOT doing much to cool the exhaust side of the piston. It helps from being in the underside of the piston and fuel that is the result of the pipe's stuffing pulse..

There exists MUCH more heat on the crown during combustion that ever is present at the exhausting phase.

[Kels]

Danny.. here is an article, I wrote years back,that addresses the back pressure .

http://www.2strokeheads.com/techcans.htm

Kels thinks this is the way it is..

[hodakamax]

Kels, you are dead on that probably all seizures are caused by the oil barrier breaking down. In this case the barrier has broken down because the oil will not lubricate above a certain temperature or worse yet been burned away. The exhaust side of the piston is just a hot place because there's a flame exiting. In modern engines we have coolants circulating in vital areas but in our vintage two-stroke we have to go with fins and the cooling effect of ambient external air and the effects of atomization of fuel, which is evaporation. I would assume that our reed-valve engines with the intake and transfer holes would benefit the exhaust side of the piston but the bottom line is that oil only lubricates to a given temperature. When this temperature is exceeded the oil barrier fails. As for oil falling out of suspension you would need an emulsion for suspension whereas our mix appears to be a solution. Granted oil does have very long molecules and could act like an emulsion but gasoline appears to only thin oil. The oil molecules are intact but further apart. The oil/fuel ratio is determined by the minimum lubricating requirements when fully mixed.

I don't think or know if we have any dispute but whatever the conditions are, the number one priority is keeping the oil temperature below its critical lubricating failure point. Raising that point (improved lubricants) can help but the answer is to adjust the cooling capacity to keep oil below those limits whatever the conditions. We could increase the fin size or use a fuel that has a higher evaporation rate or increase the main jet size or compensate with reducing timing advance or compression, whatever it takes. We can increase the amount of oil beyond what is needed but it only displaces fuel which in effect only makes the engine run leaner. Every problem we are talking about is caused by a failure of the oil to lubricate above a certain temperature.

This is a fun discussion and I'm only trying relay what I learned in years of two-stroke building and racing. Keep it cool!

Max

Kels, I did read your article--Good job!

[dcooke007]

Max,
Although we have strayed a bit, I think this discussion applies to Doug's thread. At this point it seems obvious that oil film failure has occurred. We might not agree on the cause or solution. Migration rates at high rpm's and temps still fits.

Yes, you can de-tune your engine to the weakest link but the point of racing is to beat the competition. Oh.. ah... yea.....finishing the race has to be a component of winning / finishing well. I just think, in this case, performance can be maintained at the current level by addressing the weak link and maybe improved. I just think we have a weaker than usual player that can be improved upon. That being oil quality / quantity and or exhaust restriction.

Kels,
One thought came to mind. If the exhaust is restricted for the given power level causing the oil film to burn off the exhaust side of the piston. Will the under side of the piston exhaust skirt maintain oil or burn off?

Danny

[Bullfrog]

I surely do not know the "coloring up" characteristics of Repsol oil, but certainly agree that the art of plug readings probably tends to provide more information on general operating conditions -- and based on my old fashioned experience - that plug shows general conditions of being run in a lean condition most of the time. That tentative conclusion could easily be wrong due to the changes in two stroke oils which have come about since the 1970's.

I'm quite willing to wait for Danny's final assessment of the situation cuz he's a thorough and knowledgeable guy. And Kels concerns about stinger/back pressure are excellent points. However, I'm still quietly hanging my hat on lean main jet (partly because I've not experienced engine problems with stock CW exhausts with "middle-of-the-road" pumped up engine mods).

I noticed the recent failure happened in the first race of the season - perhaps with the same jetting which was right on a hot and humid day in mid-September of 2015, but not right on a considerably cooler day in late March or early April of 2016? Why would I wonder about that? Um, been there. Done that.

Ed
PS: Will wait for more news.

[hodakamax]

Sorry Gang, I don't want to step on any of my good friends toes but I feel obligated to make my point. This engine has seized on two occasions from exactly the same thing. One more time---Too lean for the conditions. I'm really trying to help but if you don't take me seriously (I know, it really is hard to take me seriously) we are going to be discussing this for the third time. Kels has good information but the stinger is not what's causing it to seize. Its seizing because it gets too hot and could be cured by proper jetting. The stinger could be causing hot areas but it needs to be addressed as all heating problems to keep the oil from failing. We call it chasing hoodoos, there will always be ideas to lead you off track but we need to address the problem. I know I write too long and boring articles that may be hard to understand but this is really important if you are racing air cooled vintage two strokes. I wouldn't keep preaching if I didn't really, really like you guys.

Be easy on me for my lecture, OK?

Max

[MTrat]

Maybe a dumb question, but is the tank properly vented?

[Kels]

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. 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.


Sorry Gang, I don't want to step on any of my good friends toes but I feel obligated to make my point. This engine has seized on two occasions from exactly the same thing. One more time---Too lean for the conditions. I'm really trying to help but if you don't take me seriously (I know, it really is hard to take me seriously) we are going to be discussing this for the third time. Kels has good information but the stinger is not what's causing it to seize. Its seizing because it gets too hot and could be cured by proper jetting. The stinger could be causing hot areas but it needs to be addressed as all heating problems to keep the oil from failing. We call it chasing hoodoos, there will always be ideas to lead you off track but we need to address the problem. I know I write too long and boring articles that may be hard to understand but this is really important if you are racing air cooled vintage two strokes. I wouldn't keep preaching if I didn't really, really like you guys.

Be easy on me for my lecture, OK?

Max

Max.. Honestly and with all due respect... With the above "red" quote, from you, it is difficult to really take much of what you say to heart.. You make it sounds like you are the only one who has tuned a 2 stroke engine.

BUT.. I do agree with you.. This engine Will fail a 3rd time but the culprit is yet to to found and while richening up the main jet MAY allow the engine to live longer and finish an event... That does NOT make it the culprit..

There is a difference between addressing the "symptom" and addressing the "source".. you seem to want to address the 1st while I prefer the latter... The quote in BLUE above speaks to this.. How can you possibly know 100%?

For example.. I can jet ANY 2 stroke engine super rich and with this rich jetting comes the ability to do things like add a lot of timing advance, raise the compression, restrict the pipe etc. etc.. etc.. This does NOT mean that the rich jetting is correct for the engine.. It means that it allows to to get away with a "tune" that may have been dangerous without this rich jetting--> symptom vs source again...

The better solution is to determine what is causing the added heat and address that area of the "tune" . You can't just attribute all "hot" conditions to lack of fuel... Well... Kels can't anyway

This piston shows no excessive crown heat and no sign of detonation or overly advanced timing. The failure shows a very hot exhaust skirt that has wiped the oil barrier.. Lean jetting would usually indicate some elevated crown temps and I see no signs of this. Also there is no aluminum transfer on the plug..

Anyway.. this engine has the heat directed at the exhaust side skirt specifically and , contrary to your belief, this is NOT the hottest part of the piston..

So, again, richer main jet MAY allow this engine to finish a race, but is NOT the source of the heat IMO..

[hodakamax]

Kels, one step at a time. First what you posted in red was thinking out loud. If you read all I wrote you would see that after studying it I did agree that oil was indeed migrating and even admitted I was wrong and that I'd learned something. Second, I don't know 100% but I would bet with 95% odds that this is true. This is the most common cause of piston seizure (actually about 90% of the time) and it has happened twice--I'm just going with the odds. Three--we are obviously not going to change the timing or compression with jetting change, we are only trying to keep it from melting down. Four--All hot conditions are not caused by a lack of fuel but its certainly a big one. Lean engines can hole pistons and worse. Four--everyone keeps telling me that the piston shows no sign of heat except its melted. Really? Five, even though the crown is the hottest part of the piston it was the skirt that melted. the reason was it had no lubrication, the oil had failed. The crown has no lubrication problem and only fails at 1,221 degrees F. a far distance from the temperature that oil fails. and last (finally), The source of the heat is everything combined, perhaps the stinger, combustion and friction but you must weigh out the idea that you can't let the lubricant get too hot and the easiest way is to manage the jetting.

I'm not trying to discredit you or your theory and your reasoning is sound. Your last statement needs clarified and implies that leanness is not the source of heat or am I reading this wrong. Leanness can produce the 1,221 degree F. heat that melts through the crown.

I knew I would step on toes on this one but I'm getting the feeling that no one is taking me seriously and that I have no experience. I have hundreds of hours racing and engine building experience. Our bikes dominated the area racing scene for years (with zero seizures.) I detest bragging and talking about one's self but it's not like I was born yesterday. I'm trying to relate what we learned to the Gang and Forum. Enough said, I'm not putting anyone down only sharing experiences. I apologize if I've offended anyone.

Sincerely,

Max

[Kels]

Max, again.. you directly stated that the stinger is not what is causing the issue.. So this tells everyone reading that you have it figured out and you are right and everybody else is wrong.. If that is not the definition of "discredit" than I am not sure what is?

Full Definition of discredit
transitive verb
1
: to refuse to accept as true or accurate : disbelieve <discredit a rumor>
2
: to cause disbelief in the accuracy or authority of <a discredited theory>

As for your history with engines and racing.. That is great.. BUT please keep in mind... there are many others on this forum ,and others, that share that similar experience (and maybe even more).

Speaking in absolutes.. is fine if you can back it up..

Speaking in absolutes when your "absolute" can not be proven ,at that particular time, is another thing altogether...

The fact that you did NOT think oil migrated when there were several SAE papers to PROVE that it does.. speak volumes IMO... Especially , since it is the entire basis behind how a loop scavenged 2 stroke engine gets lubrication and functions.

Maybe consider having a bit more of an open mind?

None of us know everything..

[dcooke007]

Ed,
The second engine seizure was on a cold day and also a cold day when he seized the engine the first time. Both instances a cold day / lean mix immediately came to mind also. On the first seizure detonation from excess compression with the fuel used was the major cause of failure along with lean mixture. Second seizure??? I know you are just monitoring but I do have one question and this is where first hand experience is beneficial. The exhaust on Will's combat wombat is the early style flame thrower type. Is this the same exhaust you used with the stock un modified spark arrestor? Thanks.

No one is stepping on my toes....barefoot at the moment. I am considering all inputs and appreciate them. Even MTrat's suggestion about vented fuel tank. To me things have to be logical. The first seizure occurred, changes were made and the second seizure occurs but is different in that there is no detonation or excess heat on the crown of the piston. I view this as a development process.....some progress was made. Sometimes everything falls into place with a modified engine and sometimes not so. I don't want to seize another piston ...but we might. That's racing.

As with most things sometimes you have to fix the customer...that would be Will. I set his bike up last year richer than it should be knowing he is not one to address jetting changes due to temp, altitude etc.. I had also wondered about the oil he was using. Not throwing stones at Will or making excuses...just saying. We all have our own learning curve.

I will start putting the engine back together in a few days and then address tuning, back pressure and oil with my calibrated butt-ometer.... among other sophisticated highly secret testing equipment.

Danny

[tvrc18]

Did you pressure check the engine? I would pressure test and go from there. Oil brand is a hot topic but I have never seized a motor with race fuel and Yamalube R at 32 to 1. Surely you are running ethanol free fuel and a good quality oil but I would think about a oil change if jetting seems OK. I always run VP fuel because it is consistent and you know what you have. The pilot could be lean just enough to cause problems getting on and off the throttle like a mx track dictates.
Terry

[matt glascock]

I'm not familiar with Maxima products, nor can I tell when the original document was published. Also I can't see that the article describe the specifics of the oil being evaluated. Is it possible the author is describing the characteristics of castor oil? In gasoline, racing castor exists as an emulsion rather than a true solution and I would assume that its migration characteristics through a 2-stroke engine would be different than, say, Yamalube R.

[Bullfrog]

Max - may I suggest a more patient approach? Everyone on this chat group knows that you and I think the machine was lean on main jet. But I'd certainly have to say that I don't KNOW that . . . I think it, but I don't know it. Over time, the answer will be out. It isn't necessary that anyone immediately acknowledge the "rightness" of our cause . . . after all, we could be wrong! We've suggested where we think Danny should focus, but there ARE other possibilities . . . and Kels' thought is a front runner (see below).

There are SO many questions regarding this engine and its operation:

- What size carb? The stock 28 is large enough on a 125 cc engine to be a bit sensitive to atmospheric changes. If the carb is larger, it IS more sensitive to atmospherics.
- The rider is not an experienced 2-stroke guy - and doesn't do carb tuning to match conditions of the day. (and may not have a good "feel" for what an engine should be asked to do in the heat of competition)
- I'm under the impression that compression may be slightly higher than stock (I could be wrong about that) - but that could be a contributing factor.
- I'm unsure about the porting - exhaust port height, enlarged transfer passages? Just how pumped up is this engine? My impression is that it is a "middle-of-the-road" tweak (ie, stock exhaust port height). IF that is correct, then I wouldn't expect the stock exhaust system to cause heat problems. But (again) I could be wrong about that. (Note that my experience does not include overly long periods of riding at full throttle, wound out till it will wind no more. Adding that operational demand to my repertoire could "find" the exhaust system difficulty Kels is talking about with a stock CW pipe.)

So, I'm going to sit back and wait to see what answer surfaces, I encourage you to do the same.

Danny is a good thinker. He will zero in on what he thinks needs fixing (and he can touch and closely examine the parts - which we can't do). If he nails the solution, all is well. If not, he will have eliminated one more thing which is not the problem . . . and can proceed from there.

Ed
PS: Danny, I ran both types of CW pipe back in the day without problems with premium pump gas and 40:1 pre-mix - but I just cringe at the thought of full throttle at absolute maximum revs for more than a hundred or 200 yards or so (I probably couldn't make myself do that for more than the 1st hundred!) Doing that is just cruel to my little 125cc friend. It is time for taller gearing if I'm doing that on the track.