The Seizing of a Piston

[hodakamax]

I'm sure everyone is probably tired of hearing Max's lectures on Too Lean but I hope everyone reads this one because it concerns one of most important subjects ever discussed on our Forum, the seizing of a piston. I think we have become complacent in our thinking because if we are a serious racer of today we are riding or driving a liquid-cooled 4-stroke with its own lubrication system and separate cooling system. If our racer of today becomes too lean it usually just runs worse. We re-jet it or re-program it and it runs better. It has been protected from overheating by liquids circulating through the head, cylinder and radiator along with a circulating oil system.

Not so on our vintage air-cooled 2-stroke of yesteryear. Lubrication is mixed with the fuel and cooling is provided by fins, ambient temperature air and fuel along with the atomization of fuel and its evaporative cooling. A large percentage if not most of the cooling comes through the carburetor. In a race engine at full throttle all of the fuel and lubrication is coming though one hole--The main jet. If it's too small overheating is the result with the resulting failure of the lubricating properties of oil causing more friction and more heat. Detonation may start because of heated parts igniting the mixture before the spark plug does. The vicious circle has begun, lubrication has failed, friction is increasing, temperatures rise to the melting point of aluminum and it's all downhill from there.

It's easy to get off the path on this one, we all have. Our first thoughts are lack of lubrication or mechanical failure. This is always a possibility with culprits being improper clearances, too much compression, ring end gap, timing and so on. We can throw in more lubricant and possibly save the day but then we are reducing the amount of fuel to the engine with a resulting loss of horsepower and even more lean fuel conditions. We can look at melted parts and try to figure out what caused the situation, we can look at the contaminated spark plug which has been through an inferno and sprayed with liquid aluminum and on and on but the answer always is; It got too hot.

I and many of old racers of the forum have walked that path of piston seizure and we have several of examples in our box of junk. Our conclusions after years of racing were all the same: Lean mixtures are the cause of most piston seizures.

Max

[bchappy]

That would be my case. It least "most". of them.

[hodakamax]

Bill, am I leaving anything out? This will probably go to the Resonator and I can always use your expert and revered opinion!

Thanks

Max

PS--I suppose that reflections of a tuned expansion chamber recharging the cylinder could also fit into the cooling of the piston and cylinder. Waddaya think?

[taber hodaka]

But if you tune with a super good oil and then drop back to a poor oil with the same jetting it can result in piston seizure.----------Clarence

[hodakamax]

Amen Clarence! No argument here.

Maxie

PS--I also can use your respected and revered opinions. You are one of the old racers mentioned in the post!

[hodakamax]

That would be my case. It least "most". of them.

I hope I fixed your concerns with a quick edit. When you replace fuel with oil, the mix becomes leaner ON FUEL. Try that.

Max

[Zyx]

But if you tune with a super good oil and then drop back to a poor oil with the same jetting it can result in piston seizure.----------Clarence

Yes, but not from jetting. The gas doesn't know the "quality" of the oil premix, only the quantity.

[bchappy]

WOW! Max, so many things can cause too much heat. The added oil, a different expansion chamber can change the recharging and increase or decrease heat. The fins packed in mud can increase heat. You have described it well, but again in my opinion the main jet being too small "for the conditions" is the cause of "most" piston seizures. It was for me.

[taber hodaka]

Arizona -- gas knows the quantity of oil??. you are wrong or I am misunderstanding you. Gas doesn't know anything. The person that doesn't finish the race may not know the quality of oil. but the rider that finishes time after time with many wins does know the quality of oil. ' We can't just keep adding more oil until we finish a race. Do you agree about the importance of jetting? -----------Clarence

[Bullfrog]

. . . or a too small pilot jet while cruising on the back roads . . . Still a lean condition (just not the main jet)

Ed
PS: to me, "fuel" is a mix of gasoline and oil. When you increase the oil in the mix, you reduce the gasoline in the mix . . . so if the jets stay the same, the engine will be leaner on gasoline - and that can cause a seizure. (but it is the same amount of "fuel") Ah, don'tchajustluv semantics?

[taber hodaka]

I am convinced and I am going to start taking my cod liver oil soes I don't have a seizure. And I do appreciate romantics. Ed did you eber stick a engine like the rest of us?? Also Ed your statements are right on and nicely stated. ---------------Clarence

[Zyx]

Arizona -- gas knows the quantity of oil??. you are wrong or I am misunderstanding you. Gas doesn't know anything. The person that doesn't finish the race may not know the quality of oil. but the rider that finishes time after time with many wins does know the quality of oil. ' We can't just keep adding more oil until we finish a race. Do you agree about the importance of jetting? -----------Clarence

Of course jetting is important. That's a rhetorical question. But having jetted a bike using, for example, a 32:1 ratio of the best quality premix, you don't have to rejet when changing to the worst quality of the same kind of oil. Quality infers such things as oil film strength, or the type of base stock used. Using poor quality oil can jeopardize an engine, but the question was jetting. Jetting doesn't change just because you used HP2 today instead of Yamalube or Repsol, or whatever, as long as they are to be used at the same ratio. Carb pulls in gas that is 32 parts gas and 1 part oil. How then does the engine, the carb, the gas, or whatever know what quality the oil is just from the mix ratio? If you drastically change the ratio, you may need to rejet even with the same oil, but jetting has been grossly overstated in recent discussions as if it were some magic bullet, without which our bikes will fry. There is not just one single combination of jets that will work for a given situation, and I doubt any of us has regularly seen perfect jetting in our own or others' bikes. Actually, a broad range of jetting works for a given bike and set of conditions, some combinations better than others, but the engine is actually quite tolerant.

Give you an example in theory: you have a perfectly jetted bike for your favorite place to ride. On one day it is 90 degrees and 16% humidity, and the bike runs perfectly. The next day it is 70 degrees and 30% humidity. Question: do you need to rejet? Technically, yes; practically, no. I have run the same engine in my Hodaka from 1973 to 2015 in Illinios, Kentucky, Alaska, and Arizona, in summer, fall, winter, and spring conditions, and never once rejetted. I couldn't. I didn't have different jets to switch to. Did it run? Yes, for forty years. Did it run perfectly? Probably never did run perfectly and I wouldn't know if it did or didn't because I don't have a dyno. But it ran quite well always, outran an awful lot of other guys, never fouled a plug, never seized. How was that possible when recent discussion says that conditions for today if different from yesterday can cause seizure because the main jet was too lean? Nonsense.

There clearly is a such a thing as too lean or too rich, but between those two extremes lies a broad plain of useful power. And frankly, no matter what you may have attributed piston seizures to over the years, it has rarely been jetting that caused the problems because jetting, once within the range, rarely leads to failure regardless of conditions. Your power may be up or down today compared to some standard of perfection, but the engine is tolerant of a lot of changes in temperatures and humidity, altitudes, and fuel quality once reasonably jetted. I would posit that perfection in jetting is like the Holy Grail. Doesn't exist, but less than perfect jetting has been blamed for a multitude of problems that truly lay elsewhere but went undiagnosed.

[hodakamax]

Thanks for your input AZ. My article is a generalization and simplified only to make a very important point that air cooled 2-strokes are mostly cooled by intake air and fuel mix. My example deals only with a race engine at full throttle and racing conditions. Temperature is the enemy in this case because of the temperature limits of the lubricant. We must keep the engine cool for it to survive.

I thank everybody for their input on this one! I think Bill helped sum it up nicely. And Clarence for your silly humor about cod liver oil that gave me the first laugh of the day!

Maxie

PS---The article has been submitted along with my comments on Bill and Clarence along with Danny's photography. Check it out when the new Resonator arrives! (which means that some of you out there need to join us at the Hodaka Club!)

[taber hodaka]

Shorty no ones thoughts or beliefs are nonsense. I agree with most of your second paragraph. We have not been discussing mud putters but race engines that are running 150% higher rpm than stock 9000+. The vast majority of us have never seen a dino. Things that change our engines are porting, different heads and compression, exhaust, different size carbs, fuel and oil, to name a few. We are not talking about a stock motorcycle reasonably jetted, most stock motorcycles are very much on the rich side. I the late 60's a piston and ring was about $10.00 today $150.00 When you have modified your racer, traveled many many miles to race. Finishing becomes very important, as you can evaluate all of your modifications and tuning becomes the most critical. You cannot hit the track and see how it runs, you must tune it "covered in most hodaka manuals". Hope we all somewhat agree now. respectfully what name do like to be referred by? and hope to meet you at Hodaka Days-------------Clarence
P.S. Dry humor drought year.

[racerclam]

THis is getting fun ! Just a fact to consider as Shorty said the film strength is a factor in oil and I want to mention again that not all synthetics are equal. Synthetic hydrocarbon is the cheapest base stock to build oil with and that would include most oils on the market , Di Ester base was the step up and was what Amsoli used to be years ago. The the top of the line is Polyol Ester such as Red LIne uses. Alos not the all petroleum oils begin breaking down at only 280 degrees and your cylinder walls are definatly hotter than that , and that is why petrolium premix requires mor oil in hope that there will be some oil still hanging around to help out . I have whitnessed lab tests at the Red line plant to see this stuff , If you have a good oil and experience a seizure your problem is tuneing , if you tear down an engine that seized and its still wet inside the oil did its job.

Rich

[Zyx]

Clarence,

The "nonsense" comment is aimed at the notion that because the piston in the CW seized, it necessarily must be jetting that caused it, and I believe that several persons have stated as much. I am not keeping track of who said it. My thought is that while running too lean can cause seizure, so can many other things, so it isn't necessarily lean running that caused this or any other seizure. And, running lean enough to seize a piston makes the engine run so poorly that there would be no question about what caused it.

Diagnosing cause requires reference to facts. Anecdotes and experiences are not situational facts. We use experiences to sort through the facts and find similarities to prior circumstance. While some here may have seen dozens of seizures or have a basket full of scored pistons, assuming that necessarily these were caused by lean conditions sounds like a jumped conclusion. Lean running starts to express itself inside the engine by creating a hot spot in the center of the piston crown, which will show as a light color and generally ashy look, with the underside of the crown showing burned up oil residue that is flaking off from excess heat. Left unattended, such hot spots lead to preignition and metal erosion in that area. Scuffed pistons and seizure are secondary and tertiary results when caused by lean conditions.

The CW as an example shows none of the attributes of lean running. The plug color is normal to rich, the crown is not eroded in the center, the underside is a light toast color, and the video sound track does not reveal any symptoms of lean mix, which I believe was Danny's conclusion as well. If none of the symptoms suggest lean, why conclude it seized because it was lean? What I heard was that it had to be lean because it seized, and back in the day, lots of bikes seized because they were lean, therefore... That is circular logic without basis.

So no matter who may hold the notion, I have to say it is nonsense to conclude a piston seized because it ran lean unless there is empirical findings to support the conclusion.

As for premix ratio changes demanding rejetting, I would point out that there are any number of oil injection two strokes in the world whose mix ratio spans all the way from zero or 100+ to one, to 20 or 30 to one depending on throttle position. But of course, these machines don't get rejetted based on throttle position, so I have to conclude that a broad range of oil mix can be tolerated without changing jetting, even though I agree that changes in mix ratio should require addressing jetting. It isn't strictly necessary to change jets, but it may be good practice if you are running on the edge.

This is why I suggested that too much emphasis has been placed on jetting as a cause for whatever failure you may experience. If you just built a one-off and are searching for the right blend of parts, lean running could be a risk. But for a machine that runs well and has been doing so for a while, failure is rarely due to jetting issues.

[Bullfrog]

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

Ed

[hodakamax]

It seems the old racers of the past are writing this book, not reading it.

[hodakamax]

I'm done arguing on this. What we are arguing about IS The Holy Grail of 2-stroke tuning. Not a doubt in my mind. This does though bring up some interesting questions about 2-stroke oil mixtures and heat tolerances and when is adding oil to the mix is "too much." If more is better, why aren't we just running straight oil? It seems a silly question but some of the factors would be that it had no octane or too low of flash point and not much chemical energy or all of the above. If it has no octane could too much cause detonation? At what temperatures does oil combust? Bill ran mixtures of 40:1 and even less when oils were not up to the standards of today with no seizures. Displacing fuel with oil seems like a bad idea because fuel is where the energy is. Oil is probably detrimental to performance yet necessary for lubrication. No answers from me, only questions at this point but it might be fun to discuss and a way to move on.

Maxie

PS---I hope I haven't opened Pandora's Box one more time.--

[Bullfrog]

Experience from post seizure diagnosis has proven to me that lean conditions are indeed at the root of most vintage two-stroke motorcycle seizures -- but that does not necessarily mean that most are caused by improper carb jetting. Many faults can result in a lean condition, including but not limited to:
- loose cylinder stud/head nuts (head gasket or base gasket leaks)
- running the engine hard with the air cleaner element removed (when previously properly jetted with air cleaner in place)
- faulty crankcase sealing
- faulty crankshaft seals
- leaky intake manifold joints
- grunge in fuel which partially blocks the pilot jet or main jet
- improperly adjusted float level
- partially plugged in-line fuel filter
- any fault which allows air into the crankcase area or combustion area which does not arrive there by traveling through the carb
- etc., etc.

The "window width" of generally safe jetting settings for the engine gets narrower and narrower as the performance of the engine is increased through modification and (especially) as the size of the carb bore starts to significantly exceed about half the bore diameter.
Ed
PS: Of course I've seized engines . . . got one in the garage right now. Haven't diagnosed it yet . . . and time to work on it before Hodaka Days is getting short. It wasn't caused by jet selection - been running the same jetting with adjustments for altitude/heat/humidity for years. Most likely from one of the items on the list above . . . or a mechanical failure (broken ring? etc.)

[hodakamax]

Ed, Another one in the early days was no mix, only gas. I really did see that a few times in the business. Usually someone had loaned the bike to a friend who topped it off with fuel before they brought it back!

Maxie

PS--I think that was the closing of the "window width".

[Bullfrog]

Ah, but that was clearly not related to jetting or lean condition.

Ed

[dcooke007]

Max,
Most of the automotive performance folks work very hard to keep excess oil out of the combustion chamber to prevent detonation. I have to wonder if excess 2 stroke oil might contribute to detonation also. I am also sure the more oil in the fuel mix, after a certain point, performance is being lost. Like most things in life, I think to much of a good thing can be bad and a good balance is required. Same thing with our engines, the right quantities of fuel, air and oil make power and live long lives. The hard part is discovering that balance in our engines. I would love to have access to a dyno but not going to happen. At this point to discover that balance I have to use my senses, break a part here and there and most important have a good ass-ometer.

Preaching to the choir.

Danny

[hodakamax]

OK Ed, you got me, Maybe I can get out of it by saying too lean on oil. No?


And Danny, thanks for your input on oil and detonation. I was just throwing out questions.---Maybe we're on to something! assometer is it! and Hey, the 35-70 was a lens I owned and on the camera most of the time--a good one!

Maxie

[Bullfrog]

There was a dyno test reported in a magazine a few short decades ago which searched for the "balance point" between 1) more oil for improved lubrication VS 2) more gasoline for more power. The result of that dyno test (with that engine and that oil) was that 26:1 was the proper balance point. Sorry, I don't have a copy of the article. (I think the article mentioned the concept that more oil is not an automatic "less power" thing . . . because what we are after is power delivered to the countershaft sprocket . . . and reduced internal losses due to friction reduction thru improved lubrication reduces heat buildup and improves "delivered" power.)

Ed