The Seizing of a Piston

[dcooke007]

Ass-ometer = seat of the pants determination if engine is running better with a little humor thrown in.

Danny

[hodakamax]

My questions are yielding answers that I hadn't even considered. I guess that's what I like about the Forum, I've learned or at least been made aware of two things today, detonation could be caused by oil and adding more oil to the mix could actually cause a gain in power through better lubrication at least up to a point. It's always good to ask questions in hope of finding more knowledge. Thanks for jogging my brain with your reports, keep them coming and on with the discussion!

Max

Ps--Funny Danny, humor is really the best part of the Forum but Max is always getting in trouble! I guess we can have both fun and learning.

[MTRob]

Hi guys and gals, Haven't added anything in a while. In the last 3 years I rebuilt one 64 Ace 90 and my 125 Wombat. About 4 months ago I asked about why I was fouling plugs all the time, these motors were completely rebuilt, but I was was fouling plugs. Everybody told me (timing,point,condenser)
After all the years of racing I changed the fuel oil mixture from what Hodaka said. Now they both run great and I can start on second kick. It just took me awhile to get the gas/oil mixture right for where I live. So it does make a different on how they run and always have.
MTRob

[Zyx]

The oil from oil injection systems does not go through the carburetor jets . . . hence it has no effect on carb jetting.

Ed

Sorry, but it sure does.mehether the oil is mixed first or mixed last, it is part of the intake charge, takes up space, and contributes to jetting concerns. That it doesn't go through the carb jets makes no difference, it still has to be accounted for.

[BrianZ]

I would have to agree with Ed. I think that the effect oil injection has on jetting would be extremely minimal (if any). When gas and oil are mixed and metered through the carburetor jets the effect is that an increase in oil results in a leaner mixture. Adding oil via oil injection (at the manifold) would simply displace a small portion of "previously atomized and mixed" air and fuel.

Brian

[Bullfrog]

Arizona:

It seems clear that when sending a 40:1 pre-mix formula through the carb jets, 2.5% of the fuel is oil ( at 26:1, 3.85% of the fuel going through the jets is oil). Not having that volume of oil displacing gasoline at the jet is a noticeable difference when jetting with oil injection.

To be sure, in both systems there is oil flowing through the engine . . . and some of that oil burns . . . which has an effect -- so both systems must be "tuned" to work properly with those oil effects. But only one of those systems must compensate for oil displacing gasoline at the jet.

Ed

[hodakamax]

Our dissenter has argued that there are no visual signs of leanness in the center of the piston. I'm through arguing as I said but perhaps we should at least address this point. Maybe his interpretations are coming from his experience in liquid cooled 4-stroke engines. When our air cooled 2-stroke becomes too lean the heat breaks down the lubricant and increased friction begins between the cylinder and the piston/ring assembly which is where the seizure occurs. During the seizure, the piston is still being cooled from the cool mix from below and the center of the crown is probably the coolest or at least somewhat protected.
In a liquid cooled 4-stroke lean conditions heat the center of the piston. Lubrication hasn't failed and the bore is protected by the circulating coolant and the piston and rings are still receiving oil. The failure is at the hottest place which is the center of the piston which is shown in a visual inspection.
Our air cooled 2-stroke doesn't have all these luxuries and fails in the hottest place which is between the cylinder and the piston/ring.

Max

[Bullfrog]

Are we talking about the universe of vintage two stroke seizures . . . or a particular Combat Wombat seizure? Photos have been referenced a couple of times. I don't see any photos in this thread.

Ed
PS: I don't think that I can accept the concept of the center of the piston crown being the coolest part of the piston in our air cooled two smokes. There is precious little reason for the fuel air mix inside the piston above the wrist pin to flow/move/carry away heat -- it is sort of a stagnant volume -- unless we are talking about a Combat Wombat piston with Victory Port (or a reeded engine).

[hodakamax]

Ed, I said (or meant) that the coolest part of the piston DURING the seizure, (I did edit that) was the crown because the outside of the piston is starting to melt, caused by friction between the cylinder and piston/ring. During normal operation the crown would be the hottest but within the heat limitations of the metal. Transfer holes through the piston and cylinder certainly do help the situation as illustrated in Danny's CW by the major damage being on the exhaust side of the piston.

The pictures are on Danny's post; Tired Combat Wombat.

Ed, you're right again and I hope this better explains what I was trying to say.

Maxie

PS--The air/fuel mix is not totally stagnant below the piston due to turbulence and is being constantly replaced providing at least some cooling of the crown but certainly not as much as a reed valve set-up with transfers through the piston. Also, even if the cool mix is it is somewhat stagnant below the piston crown, thermodynamics still send high energy to low energy environments. Good point Ed.
.

[Kels]

Hello guys...

1st post on this forum.. While I do not want to get into what our studies have found with the oil and and fuel.. I would like to comment on the seized engine..

IMO, the cause of this failure is detonation.. You can clearly see the the detonation on the crown edge..
The question is.. Why did it detonate?

Again, IMO, the reason behind this detonation is directly related to the coated piston crown and head.

If the coating is a TRUE heat barrier (many claim to be but are not) then this can cause some issues with keeping both the good heat (the heat energy that makes power) AND the BAD Heat (the heat that needs to be dissipated) .

1st rule of thermodynamics..and I will summerize and simplify... Energy can not be created or destroyed, it can only be converted/transformed.. When you effectively (and I say this loosely) keep the heat from leaving the cylinder via cooling fins, then you STILL have this heat in the cylinder.. remember, it can not be destroyed... Now, you have added heat and it is building with every stroke. You MUST adjust for that... If you do not failure will occur..
With the poor cooling capabilities of an air cooled engine, this becomes even more of an issue (vs liquid cooled system)... This bad heat will continue to build until you have a failure..

[hodakamax]

Kels, your report is interesting. (Welcome by the way!) It takes Max quite a while to think things through so I'll ponder your prognosis. I have never used any of these coatings as they were after my research days. My early opinion was that they were good because they reduced friction on the cylinder and piston. I didn't see any reason to coat the top because I personally never had any crown damage in my racing experience.(except for parts such as rings, passing through the combustion chamber!) This is certainly a good topic to be discussed but Max has zero experience.

I agree that detonation was going on but I think it was caused by the glowing ring setting off the air/fuel mix before the spark plug did.(and at bad times, mocking too much spark advance.) The detonation was after leanness heating had caused the lubricant to fail, causing cylinder/piston/ring friction heating that resulted in a melting of the the piston.

In my opinion, as you say, I give the odds on this one at over 95% chance that this engine was too lean "for the conditions". This is not an uncommon failure.

Thanks for your opinion for sure! I hope the gang discusses this one on coatings and heat transfer.

Max

[dcooke007]

Thanks for your opinion for sure! I hope the gang discusses this one on coatings and heat transfer.

Max

You just cant help yourself...can you.

Danny

[hodakamax]

At least the Forum is on a roll again!

Maxie

PS--My fingers hurt from typing, I've never typed this much in my whole life! (It's a good thing I know nothing about coatings and heat transfer.)

[Kels]

Kels, your report is interesting.
I agree that detonation was going on but I think it was caused by the glowing ring setting off the air/fuel mix before the spark plug did.(and at bad times, mocking too much spark advance.) The detonation was after leanness heating had caused the lubricant to fail, causing cylinder/piston/ring friction heating that resulted in a melting of the the piston.

In my opinion, as you say, I give the odds on this one at over 95% chance that this engine was too lean "for the conditions". This is not an uncommon failure.

Thanks for your opinion for sure! I hope the gang discusses this one on coatings and heat transfer.

Max

Max... ask yourself.. why was the ring glowing? Why was the HEAT too high? Why did the oil barrier fail?

Wouldn't an engine with MORE cylinder heat, basically a cylinder and/or piston that is too hot internally, (let's say,at this point, that this is due to the barrier coatings)-->require more fuel??

I think we may be at the Chicken vs. the Egg stage???

[hodakamax]

The oil barrier failed because of the heat generated by too lean "for the conditions". The oil was burning and and failing to lubricate causing even more heat. The ring was heated by friction with the cylinder and began to glow causing detonation. What we need to figure out is wether the insulating coating was storing heat in the piston, helping or hurting the situation. I haven't a clue at this stage! I claimed ignorance on coatings and heat transfer and tried to pass it on to the gang.----HELP! I do see what you are saying, I just don't know.

Max

PS--If what you say is true, it would need more fuel to cool it which means that it is too lean "for the conditions", one of them being the coating in your case. Hmm--just what I've been saying all along!---Egg, I think, maybe.

And Danny, you are right again, What was I thinking?

[taber hodaka]

Someone is setting a record of post here, And I have used the dictionary looking for words I can't spell or even find in the dictionary. All I care about is how well it runs next time. We will all be following the results of this bike and rider. We are all jealous of the builder ,tuner and rider. We all want to tune it or just add more oil. Nobody just want's to just argue about it do we?----------Clarence

[hodakamax]

Clarence, I was saved by "Spell Check" many times on this one! I've followed Danny's posts from the beginning on this project and I too can't wait for this thing to fly. I'm sure it will be successful! (and I'm done arguing. I think.)

Max yet again.

[dcooke007]

Just like you guys I cant wait to get the bike going again. Will seems to be a good and aggressive rider. I am working hard to be a good builder and tuner. The bike has potential just needs more development.

Danny

[hodakamax]

Kels, Back to the coatings and heat transfer. It's fun to argue and discuss such matters but research is the way to go. A simple test with two engines with coated and uncoated parts under the same conditions could quickly resolve this problem. Surely the manufactures of these products have testing results on their claims. I wonder if any unbiased tests have been done anywhere that show if they really work or are detrimental.

Max

Max did not do well in the thermodynamics class.

[dcooke007]

Seems to me with the heat transfer thing and coatings some basics should apply. The ability of our engines to perform work relates to converting chemical energy into heat energy. Heat and pressure generated by burning fuel and air mixture acting on the piston converts heat and pressure to perform mechanical work. So in my thinking I am not sure there is such a thing as good heat and bad heat as has been stated. The more heat and pressure generated the more force to perform work...or so it seems. The problem is when you exceed the limits of the engine materials, oil and fuel. If the term bad heat indicates when those limits are exceeded so be it...I can live with that. In my mind generating the most heat and pressure in the combustion chamber is the goal for maximum performance within the stated limits of materials, oil and fuel. If that can be accomplished across the entire rpm range all the better. Tim the Tool Man theory maybe?

The purpose of ceramic coatings applied to the crown of the piston should be to insulate the piston from excessive heat. By limiting heat transfer to the piston more energy in the form of heat is available to perform work. Also, with less heat transferred to the piston clearances should be more stable and less likely to reduce due to temperature, oil film temperature loads are reduced and should overall be a better operating environment for the piston and ring. The moly skirt coating should reduce friction and provide a margin of safety should there be a momentary failure of the oil film. If these functions of the coatings are accomplished and long lasting I can only see them as being something I would want.

The purpose of ceramic coatings on the combustion chamber of the cylinder head are to maintain more heat in the combustion chamber to perform more work. In an air cooled engine this may be where ceramic coatings could be a concern. In engines with marginal cooling like the Hodaka 250's it could make a bad situation worse. In other air cooled engines with better cooling there may be some room for performance increases with out generating excess damaging heat.

One thought I have is the tuning in a coated engine may be different from the same engine with out coatings. Coatings on the piston I cant see a down side to as long as the coating performs its advertised function and the engine is tuned accordingly. Ceramic heat barrier coatings in the combustion chamber of air cooled engines raises some concern. Will's combat wombat engine will be evaluated for coating performance at the end of this season.

Running as fast as I can and ducking for cover.

Danny

[dcooke007]

Ok, something really funny.

Two sisters, one blonde and one brunette, inherit the family ranch. Unfortunately, after just a few years, they are in financial trouble. In order to keep the bank from repossessing the ranch, they need to purchase a bull from the stockyard in a far town so that they can breed their own stock.

They only have $600 left. Upon leaving, the brunette tells her sister, "When I get there, if I decide to buy the bull, I'll contact you to drive out after me and haul it home."

The brunette arrives at the stockyard, inspects the bull, and decides she wants to buy it. The man tells her that he will sell it for $599, no less. After paying him, she drives to the nearest town to send her sister a telegram to tell her the news. She walks into the telegraph office and says, "I want to send a telegram to my sister telling her that I've bought a bull for our ranch. I need her to hitch the trailer to our pickup truck and drive out here so we can haul it home."

The telegraph operator explains that he'll be glad to help her, then adds, "It's just 99 cents a word." Well, after paying for the bull, the brunette only has $1 left. She realizes that she'll only be able to send her sister one word.

After a few minutes of thinking, she nods and says, "I want you to send her one word: comfortable."

The operator shakes his head. 'How is she ever going to know that you want her to hitch the trailer to your pickup truck and drive out here to haul that bull back to your ranch if you send her just the word "comfortable?"

The brunette explains, "My sister's blonde. The word's big. She'll read it very slowly ... com-for-da-bull."

Danny

[hodakamax]

Danny, This all sounds reasonable too me.(not the bull thing but the coating thing) Good presentation and thanks for saving me!

Maxie

PS--I think I'm hiding for a few days.

[hodakamax]

Just a few more notes on detonation. Pre-ignition and detonation are two different things technically speaking today. In my racing career beginning in the 1960s, Pre-ignition and detonation were one and the same at least as the early racers were concerned. I noticed in our discussion no one called me on this one but it was the language of the day. This is just to clear things up before Max gets into trouble again!

Max

[Kels]

Seems to me with the heat transfer thing and coatings some basics should apply. The ability of our engines to perform work relates to converting chemical energy into heat energy. Heat and pressure generated by burning fuel and air mixture acting on the piston converts heat and pressure to perform mechanical work. So in my thinking I am not sure there is such a thing as good heat and bad heat as has been stated. The more heat and pressure generated the more force to perform work...or so it seems. The problem is when you exceed the limits of the engine materials, oil and fuel. If the term bad heat indicates when those limits are exceeded so be it...I can live with that. In my mind generating the most heat and pressure in the combustion chamber is the goal for maximum performance within the stated limits of materials, oil and fuel. If that can be accomplished across the entire rpm range all the better. Tim the Tool Man theory maybe?

The purpose of ceramic coatings applied to the crown of the piston should be to insulate the piston from excessive heat. By limiting heat transfer to the piston more energy in the form of heat is available to perform work. Also, with less heat transferred to the piston clearances should be more stable and less likely to reduce due to temperature, oil film temperature loads are reduced and should overall be a better operating environment for the piston and ring. The moly skirt coating should reduce friction and provide a margin of safety should there be a momentary failure of the oil film. If these functions of the coatings are accomplished and long lasting I can only see them as being something I would want.

The purpose of ceramic coatings on the combustion chamber of the cylinder head are to maintain more heat in the combustion chamber to perform more work. In an air cooled engine this may be where ceramic coatings could be a concern. In engines with marginal cooling like the Hodaka 250's it could make a bad situation worse. In other air cooled engines with better cooling there may be some room for performance increases with out generating excess damaging heat.

One thought I have is the tuning in a coated engine may be different from the same engine with out coatings. Coatings on the piston I cant see a down side to as long as the coating performs its advertised function and the engine is tuned accordingly. Ceramic heat barrier coatings in the combustion chamber of air cooled engines raises some concern. Will's combat wombat engine will be evaluated for coating performance at the end of this season.

Running as fast as I can and ducking for cover.

Danny

Danny..

Good post... and this type of reasoning is sound.. But you still have physics in play here and in an IDEAL world all this heat would be converted to usable energy and provide more push on the crank train.. But we all know that we do not live in an IDEAL world.. This is where it gets real..

Without writing a novel... you NEED to have this heat dissipated or it will continue to build and build until you have super-heated the internal components (rod, bearings, etc) and you effectively make the intake charge less dense/effective due to the heat of it..

Again... remember this heat has to go somewhere do not assume that it is ALL converted to energy and safely exited out the exhaust pipe.. That is the IDEAL but not the reality..

When you LIMIT this dissipation of heat it gets absorbed by other components!

Coated head chambers will simply TRANSFER that heat to other areas of the engine. same with the coated piston top...
It is about the time relationship...think of grabbing something HOT with your hand... you can grab it for a very short period and then you have to release because the heat has built up beyond a point you can tolerate. Same with an engine.. It can tolerate this heat for a certain period of time... then it becomes intolerable and then this is when damage will occur.. Hence the need to RID the engine of this heat.

Piston crown coating.. Same thing.. what is not absorbed thru the crown then dissipated via the rings and the rest of the piston.. will be present ELSEWHERE on the piston and it will continue to build and build..

Skirt coatings?? kind of a gimmick item IMO... once the oil barrier fails, no coating will save your engine..maybe for a split second it will survive longer.. but failure is imminent.

Think of this: You can not have a normal engine piston seizure unless the oil barrier fails!

Anyway.. Coatings can work but studies, experiments, papers etc.. have shown that they promote detonation and very different jetting is required to successfully run true heat barriers on 2 stroke engines.. Not so much with a 4 stroke because they have more TIME to cool things down..But on a 2 stroke... time is what you do not have .. Heat is great right up until it is not so great!

[Zyx]

Don't really have much else to say here, but two things: "energy can neither be created nor destroyed, only transferred or converted."

I don't think so. The maxim is that "matter" can be neither created nor destroyed. Not so sure about energy. Energy can be created through work applied. Take kinetic energy for example. A ping pong ball sitting on the edge of a table has potential energy but no kinetic energy. Rolled off the edge, that energy is converted to kinetic, and so the potential is realized. But what happens when you pick the ball back up and put it on the table again? It has the same potential energy as before, even though that energy that it had to start with was converted and lost. Whether energy put back into something has been created outright or transferred from elsewhere is moot. But I don't recall the maxim as applying to energy. Maybe I am wrong.

I have no idea if the same holds true for heat, but if it doesn't hold true for potential/kinetic energy, it isn't a maxim, maybe only a useful theory. Heat being only one kind of energy, I am not sure how to draft a proof on the question. If energy can't be destroyed, then arguably energy is an infinite thing, not a finite thing, and frankly I think the universe has a finite amount of energy within it, so if consumed, it's gone. Kind of like perpetually motion.

Second thing: detonation isn't caused by hot spots. That would be pre-ignition. Detonation is a flash burn started by a spark plug at the right time, flame spreading at a given rate, and then something upsets the balance, usually in the squish band, and the flame front goes from sedate to exponentially fast. That flash bang is detonation and it beats the starch out of engines. The something that sets it off is usually low octane, moderate engine speed, too high compression for the gas in use, and lots of throttle. As engine speed rises to near redline, detonation recedes. Detonation one thing, pre-ignition another. And there is no such thing as pre-detonation, which term has not been used here, yet, but has been used in a lot of other places on the net. Just wanted to nip it just in case.

Oh, and all seizures are caused by breakdown of the oil film on the piston/cylinder wall. What causes the breakdown is variable, but unless the oil breaks down, nothing seizes. That's' three things. Sorry.

Y'all can go back to the running discussion.