It happens that you drive here, you drive... ...and on you, without trial or investigation:

Is this picture familiar? Well, if only on someone else's example: the cost of dating is quite high ... I can definitely say that the problem today is highly relevant and certainly not a legacy of distant times. Quite the opposite: one has only to search the Web for owners of equally priceless exhibits, as there are a lot of examples:

Here is a similar example from my collection:

My question is: what is this, right in front of us? What will be the opinions?

Let's guess: "bad gas"...

I can’t resist a small digression: what exactly is being studied in this most detailed article, which is shoved into all forums. You know?!

What's this? The older brother of the piston of the T-34 tank? In a brochure for the 21st century, from the leading and most modern manufacturer of piston groups?! The creator of this piston in old age caught the dawn of the era of tube computers. The photo, probably, was picked up from photographic plates - it did not expect to live until the time when it hits the computer screen ... These are the same brochure designers who pee, which pistons squeeze by 30-40% of the mass and the rings of turbocharged small cars are flattened to 1.2 mm height?! The pistons themselves have already become as tall as the old skirts:

Didn't they find anything fresher for illustrations? Okay, let's eat what they give:

Yes, this entire brochure, without exception, is built on examples of ... diesel engines from commercial vehicles. The connection between modern forced gasoline small cars and multi-displacement diesel slow-moving vehicles, from the piston times of the Second World War, is very illusory. Everything is different: manufacturing technologies, revolutions, tolerances, gaps and even combustion phases. Why ordinary car owners and their problems are categorically Not needed manufacturers, I have explained many times and in several articles.

No one will ever finance commercially meaningless events, creating a fundamental base with investigations of causes and against themselves. How do they act in such cases? Of course, they confine themselves to the general words of the obvious captains. And what are they giving us as a reason?

We leaf through the "research" from colleagues in the workshop (evil tongues say that in the literal sense - globalization - look who made the N52 piston engines in different versions - one drawing for two manufacturers):

Tell me honestly, what category of readers is this naivety for?! Let's abstract from the specifics of the blog, just tell me how you read about "lack of water" and "mass air flow sensor", coupled with "loose V-ribbed belt", in the article about the causes of piston burnout ?! Just curious, nothing personal. Arranges?!

I am compelled to state again.

In short, in any unfamiliar situation, ask "Have you fallen into a hole?".

Yes, just:

What do we see?
- Damage, sir.
- Where do we put them?
- To detonation-s and subsequent glow ignition!

And what is in theory the cause of detonation (breakdown of the combustion front)? Yes, you guessed it: the mixture itself (its quality), its untimely ignition and accompanying conditions.

Further, we break the "obvious" reasons into subgroups and push everything into each that squeaks, but climbs. Well, for example: if the mixture is "incorrect", then who is to blame - the mixture formers. And we have them, as you know, from the intake manifold with its suctions, to the MAF and the oxygen sensor. What do we have because of the untimely ignition - yes, anything - from the timing phases, to, as they called it above ... "top dead center sensor". If you think I'm joking - re-read, there is a quote at the top. This is such a fun concept!

Again "Why did he die? - Lived!". And so in everything and always. Amazing expertise and determination of cause and effect relationships. If you want to know why the tire quickly wore out - blame the driving style and the roads - 100% profit.

Colleagues, it won't work here. Alas. I have to remind you once again that a modern engine is regulated to such an extent that it cannot sneeze without a check engine. I have already why it is very difficult to fasten 100500 causes of damage to the engine of the Stalinets tractor to the 2012 Opel Astra.

And when all of us (including me) repeat for the 101th time about "general overheating, poly-V-belt with a defective thermostat" and so on, it's better not to look the car owner in the eye ... It's better just about "bad gasoline" - it's easier and easier for everyone clearer. All in all, I don't know about you, but I'm definitely tired of it.

So those who have shame, at some point, will still believe the unfortunate that THERE WAS NOTHING, JUST went and "zatroilo". bugs DID NOT HAVE. overheating NOT was. Motor NOT SHAKE. "Gas to the floor" too DID NOT PRESS- just threw up in city mode (on the highway). Everything was so smooth and it was ... burned out.

If this is true, then all home-grown Ph.D.s, as well as Mahle and Kolbenschmidt, run into a concrete dead end - they will be forced to distrust the owner.

And we, lovers of technology and mysteries, will try to believe and figure it out.

Let's say. A clean car comes to you, of the mistakes - only a pass on a burnt-out cylinder. The mileage is ridiculous - tens of thousands, no one has ever climbed into the engine, etc. So what do you say to him in this case? AGAIN BECAUSE OF DETONATION (BEZIN)?!

You see what's the matter: on the remaining three cylinders, the "burned out" car drives quite cheerfully, accelerates and does NOT ring "gas to the floor". At the same gas station, it reached the service. I can right now, as it is fashionable, "hand over gasoline for examination", but in reality this will be done only by those who do not understand the meaning of this action (both examination and the concept of "detonation"). Its results for our investigation are already clear - I started with this.

If you also want to understand what it is and how you can “not notice it”, then try gasping the car on a reference mixture of heptane and isooctane 80/20 (easy to get, I tried), feeding the mixture from an external canister, well, or directly to yourself Splash AI-80 (this is not a laboratory standard, but close). Here is the detonation. IT'S IMPOSSIBLE TO NOT NOTICE. It is impossible to drive for a long time and "not notice" this. But even if you are so insensitive, the knock sensor will simply not allow the engine to spin up normally. The car will be terribly STUPID, twitching and ringing.

Worse than that - short "tinklings" are suppressed by modern DMEs literally in a matter of actuations - this tenths of a second, consider that almost instantly. If the car DOES NOT ring in transitional modes, then in the mode of an ordinary urban toshnilov, it will not even ring.

Well, ALLOW, it rings and sticks, but you are crazy - you still want to drive, with a breeze and in a dull car!

Well, here's an indecent picture for you - close-up burnout - you can clearly see that the aluminum has melted and flowed out, as in a thousand similar cases.

Of course, you remember that aluminum alloys begin to melt at temperatures far, oh, so over 500 degrees Celsius! Five hundred degrees Celsius. With low-power nausea (if we are talking about a normal and accurate ride, without rough annealing), it is 300-350 degrees colder even at the bottom of the piston - the speed is low, the power released is relatively low, the exhaust gases, judging by the sensor, are barely under 500 Celsius reach...

But you are crazy, in spite of the knock sensor, you start street racing in a traffic jam, the car rings and sneezes, throws errors (misses - the motor wheezes and twitches), heat up the pistons to 500+, one of them (!) Can’t stand it and leaks, then you catch on, clear your memory of mistakes and come to the service to lie that you drove quite calmly, didn’t touch anyone, you only read about detonation and bad gasoline in books ... But now remember the damned gasoline scammers for a long time!

This is the kind of idiocy that "specialists" heal us (along with a clogged air filter, suction, air flow sensors, oxygen sensors, wrong ignition angle, timing phases, red-hot valves, candles with the wrong glow number, diesel fuel in gasoline, oil dilution and other nonsense)

Do you see what's the matter, gentlemen, engineers, what are you worth if the DME sensors working under your strict guidance and tuning cannot prevent such a problem ?! What questions to the owner then, who managed to rush around in a detonating and choking car, and after that "does not remember anything"?

But today I will upset you very much, I will specially take a large photo from the Web, similar to what I can do myself.

Look at where and how all the aluminum leaked out:

This is called TDC - top dead center - "melted" as if by a ruler on the lower boundary of the combustion chamber!

Let's once again consider the conditional "triangle" of such a "temperature gradient":

Let's compare with the piston from my collection, for a clear understanding of the fact that all such situations are like a blueprint:

Well, in this case, as in many others, here the rings are also located "as if on a ruler":

You have not forgotten that detonation is actually an explosion (and that the energy of an F-1 grenade explosion is no more than in an ordinary lighter). The speed of the front propagation is enormous, but the energy is stored in oil - almost for milliseconds!

Lightning has a huge voltage and a fantastic amperage, only a meter with kilowatt hours will wind up hardly 100 rubles in one flash. How many such blows need to be hammered in order to heat the piston to a melt? We'll talk about that below...

All the photos show melting (melting) and there is nothing like a short-term low-energy process, and (or) a series of processes ... there, most often, there is no obvious mechanical failure at all.

How many microportions of fuel are required, the explosion of which is accompanied by clearly visible mechanical shocks, in order to locally (in one narrow sector) heat the piston red-hot so that it flows out strictly at top dead center?

In general, as always, the owner did not notice ANYTHING, drove normally, there were no errors, there was no whole list of malfunctions. And the piston burned out.

It burned out, as it were, from detonation, but ... strictly at TDC, when there could be no "detonation" in the sense of "failure of normal combustion", and its energy simply would not be enough ... Detonation dealt with the piston extremely correctly - heated it locally to the temperature of the melt and burned through. Accuracy and accuracy in all such cases is amazing - a virtuoso series of continuous point explosions ... that no one noticed!

And do you know what the owner actually "kept silent" about when he did not lie to you that there were no mistakes ... he just drove calmly?

He most often “forgot” to say that he periodically and abundantly tops up oil in his engine (the manufacturer considers this to be the “norm”, so when it really became the norm at the 3-4th year of the engine’s life, he was mentally ready for this - what can I say, when it says so in the manual).

Here are some videos of used motors that were dismantled for overhaul:

There are quite a few videos like this on the web. They are called differently, but the essence is the same for everyone - thin "modern" rings are either thermally "hooked", or coked and blocked in the grooves (but the option when they are like that from the factory is certainly possible - all the time):

Take a close look at all examples of damaged pistons: rings there are severely tamped inside the grooves- their profile doesn't even show up! Why did it happen?!

These are silent witnesses whom no one (yet) has interrogated properly.

Now think about what happens when a piston dangling in all directions (including the longitudinal) reaches TDC, for example, with an "uncompacted shift":

He does this cyclically and almost as caricatured as in this picture - it’s lucky that the piston was depicted without sealing rings.

Yes, having studied several similar cases, I contend that when piston rings are flimsy, they easily coke, sag, and almost completely cease to perform their SEAL function, being squeezed into the groove. In this case, the chances of locally heating up and burning through the piston (or breaking the baffle with the same overheating) are extremely high! This is a cyclical process that takes place over a relatively long time. together with normal combustion near TDC- the process is completely controllable and monotonous, not manifesting itself in any way.

This is how the gaskets and seals of direct injection fuel injectors "burn out" - just give the mixture a little access and the ring of the intra-cylinder seal will burn out literally in hours - it will evaporate.

At the moment of the working stroke, the combustible mixture rushes exactly where it does not meet the former resistance - into the gaps that are not sealed with rings. It will not take much time for the "microcombustion chamber" created in this way and found by the mixture, all the energy of which goes to warming up, to burn another "fatal triangle" in the piston. The piston melts imperceptibly, literally during one relatively quiet trip, at the moment when the access to the critical portion of the mixture becomes stable and constant.

Do not repeat other people's mistakes - the cause of such "burnouts" is in no way connected with the phenomenon of detonation of the fuel mixture and glow ignition. All the "original sources" (and those who repeat after them) are mindlessly replicating antediluvian nonsense.

Let's consider the situation in more detail.

So, the initial conditions, as a set of specific situations: a person was driving along the highway, in the usual highway mode, NOTHING I didn’t notice anything unusual and suddenly ... rrrr-time: the car thickly spits oil into the pipe and the engine starts to “troit”, the “check” lights up. A person comes to the service, they get a piston there. The piston literally flowed out - melted like a candle.

The person asks: "Hey, what did I do wrong?!"

In response to him: "According to the most detailed explanations from the manufacturer of piston groups, which we are guided by, this is nothing more than detonation (later also glowing) combustion - overheating + self-oscillatory process with self-ignition from hot parts. "Gasoline is bad."

Okay, let's say.

Can you imagine the visibility unphased ignition in a modern engine, with a knock sensor? The mixture either simply detonates, or is ignited too early (literally - "pre-ignition"). In both cases, it is impossible not to notice this in the operation of the engine - expanding gases work towards the piston.

Therefore, when the owner is asked about the likely knock-shaking from the engine,

and he answered - "no, well, just trotted ..."

"Goof, I didn't notice," sums up the seasoned serviceman...

Now a somewhat later explanation about "what does detonation have to do with it." Let's go back to the original source:

The reasons mentioned here are well characterized by a faulty motorized stagecoach of the late 19th century, when, obviously, the lead angle was still regulated on the steering wheel. It’s hard to squeeze such terrible nonsense into a modern motor in 30 years so soon ... Yes, all this can be imagined anywhere ... except for modern engines. But also miss any of these signs?


Why is a long list of this nonsense pushed into the root causes of "burnout of the pistons"? It's simple: the main reasons for the occurrence of detonation combustion are described, which will lead to overheating of the motor and (errors with the choice of glow number for candles are added here!) The occurrence of local overheating - that's, like, they melt - they overheated.

They don’t even try to explain where the glow ignition came from “out of the blue”. At the same time, the word "detonation" is not formally mentioned even once (in this document). It's like "no hands, no legs, blind and deaf, but no one told you about a disabled person." Well, try to "set the ignition timing incorrectly", organize "choke", "blow" the engine on a chip and set fire to the "wrong grade of fuel". To "not notice". And only after that, so that the car that shuts up and shoots all over the street also overheats to a stable glow ignition.

Well, I’ll take a picture, which, indeed, is extremely similar to detonation, with all the attributed paraphernalia - it looks like a forging - the piston was “hollowed”, both along the bottom and along the edges - full of serifs and floats. External - clearly coming from the combustion chamber.

Now let's kindly use another picture, about which Ph.D. writes literally the following:

"Classic detonation", they tell us! Doesn't it bother you, lovers of the "detonation" classics, that they hit you on the head with a tire iron, and your shoelaces are untied ?! Why is the aviation piston broken and pounded as it should be, through the top, and the splits on this piston are similar to the explosion of a neutron bomb in Soviet jokes: the “detonation” did not notice the bottom of the piston itself, but only reached the lower jumpers ... This is some kind of special detonation ?!

And let me show you such pistons from my personal collection, take a look:

Once

Two...

You know what's embarrassing?

Bottom:

An ideal "oil-burning" bottom with a soft layer - long-lived "live" oil on it - carbon semolina. Estimate the layer depth by notches with the cylinder number and the piston pin plane indicator. The presence of such a bottom is an iron guarantee that the layer DO NOT TOUCH no metal shocks, no heat.

Are you sure that at least once (well, once, maybe, when it was, there is no doubt) it was hammered with early ignition of any kind ?! So much so that they managed to overheat (?) And hollow out the jumpers that are UNDER the bottom. Do you see any signs of local thermal overheating on it? Spots? Is it possible to artificially form such a homogeneous layer, then "anneal" part of it and knock on top so that there is no trace on the very bottom, and continuous destruction BELOW it? And neither the owner nor the knock sensor (the engine itself) noticed this (the "tapping" process)?

Then this body of water suffered from underwater nuclear tests an hour ago, don't you agree?!

Separately explain how such strong blows, not affecting the piston crown are transferred to the level 2-3 of the jumper?!

And now let's look at the fragments of the jumpers themselves. For beauty, I took a couple, with two different pistons, from different places:

Their fracture has a quasi-ideal, almost mirror-like surface. The reason is simple: it thermal expansion chip. The metal was heated for a long time in a compact zone, could not stand it and BURST. Part of the jumper simply stood out - thereby removing the resulting voltage.

And now let's look at the "cold destruction" - when the metal was really gouged by mechanical action:


Do you know what is here, what was missing there? CRUMPS. Cold seams are easily stained. From the impact, the silumin crumbles, it will not give a smooth glossy surface - it will give a gray, porous, rough one.

Hit the piston with a hammer:

For jumpers bursting from temperature, you simply apply a piece and an even seam is obtained immediately and without effort - there were no crumbs:

Of course, this is not evidence - so-so, first-order doubts.

But now we will make servicemen and candidates of science sweat:

Look: aluminum leaked out as if from a fixed piston, and even stuck perfectly to TDC. What sort of obturator works there that, with dozens of useful strokes per second (!) retained such an outstanding, most accurate imprint?!

And here's another, and everything is the same - the pistons melt strictly at TDC:

Few? Let's continue - TDC:

Would the piston gouge out of phase (knock disruption, glow ignition) in the opposite direction, would it have dirtyed it below AT LEAST ONCE? At least one parallel drawing was below!

"So this piston" collected "aluminum", - on the left it burned out, therefore it was "not tidied up". - The quality of "cleaning" is the highest! A specially fitted scraper would not have been able to assemble it, let alone a leaky piston dangling with a gap in the cylinder. But you know what's upsetting? On the wall of the cylinder there is a hon, about 5-6 acres deep. It would be impossible to pick out aluminum powder from it with a piston rough in profile, it would be enough just to lean / grind it there, which is why, even after removing the powder by intense sanding, the walls can still be "tinted" in gray.

Let's try again:

We fix:




Brought to condition:

A couple of tens of minutes have passed:


Ready:

The only possible mechanism for the formation of such a clear imprint of leaked aluminum strictly at TDC is as follows: the piston is “annealed” along the edge for a long time in the normal combustion mode, strictly at the point specified by the engine control system. On the cold wall of the cylinder, it "draws" with the help of a synchronized pressure surge from the expansion of gases (a plane perpendicular to the propagation of the flame). This occurs in conditions of extremely timely ignition - these are many thousands and even tens of thousands of cycles (revolutions * time / working stroke). At some point, another pressure peak separates a large piece of heated melt from the piston, and this ALWAYS happens clearly near TDC.

1. What is this article about?
On the real causes of piston melting and breaking of piston bridges in modern(sic!) engines.

2. Why do pistons melt in this case?
From the penetration of a combustible mixture below the top zone - into the compression zone, where the flames are passed by buried (very weakened, incorrectly calculated) piston rings.

3. Yes, what difference does it make to me, what is the real reason ?!
The difference is simple: first they fill you with "oil with all tolerances, which is specially designed for your engine", then they allow you to change it at 15, 20 and even 25 thousand km (sometimes 30-35 happened!), even further - they announce that normal oil consumption - up to 7 liters per 10,000 km (seven liters, Carl!). And for sports cars - and all 15! When your car really starts to eat oil in liters, in the end, with a high probability, either the piston burns out (or the jumper / partition breaks off). And here they tell you: bad gasoline is to blame - detonation and glow ignition! Bingo - no one is to blame, except for the tankers and you (you yourself found this gasoline!). No warranty repair and a hint of one. You still can’t prove anything (neither to the dealer, nor to the gas station), but at least you won’t be under the illusion that this is “an unfortunate accident from our bad gasoline.” In other words, who is warned is armed.

4. Well, the burnout is clear, but the detonation clearly breaks off the jumper - there are no traces of melting, no traces of flame access!
When the motor actively eats oil, the rings are tightly clogged with ash, which envelops the ring all-round (including the depth of the piston groove). This blocks the cooling of the piston - its connection with the cylinder wall. In addition, the departure arm increases - the load itself on the jumper in the relay. Since the open ring is constantly and rigidly "shifted" in the groove by a reciprocating motion, sooner or later, such a load simply breaks off the overheated jumper ...

5. Obviously, the pressure on the jumper through the ring breaks off the jumper at the moment of detonation ...
That no one noticed, yeah The heated (not to mention overheated) piston-cylinder gap is literally microscopic, and this is a very curious physical theory: if a bomb is blown up above the roof, the fireplace on the first floor under the chimney will blow to pieces, and the roof will remain intact?! And the beats of the drum kit outside the studio door "crawl" through the keyhole - you can hear it as well as without the door?! I have seen hundreds of "detonation pistons" in practice, with runs well over 200 tkm: there is no living place on the piston from detonation, and at least henna for jumpers, if the engine consumes oil moderately, of course. The photo shows a DRY piston of a serviceable motor, although it is completely pitted with detonation:

6. Who is at risk?
This includes owners of modern small-sized turbo engines with volumes of 1.2-1.8, from manufacturers such as VAG, GM, and so on: everyone who clearly falls into the European school of engine building. I'm not talking about Asians yet. The higher the specific degree of forcing, the greater the chance of all of the above. By the age of 3-5, (the car is already out of warranty), the engine begins to actively consume oil. The picture is aggravated by possible factory piston errors, poor choice of oil, rolls in oil (over 10,000 km). I think that the average point of no return is about 5 years of ownership. Example: the first 3 years of the conditional "norm", 4 and 5 - the beginning of problems with abundant oil topping up. And, finally, the final season starts from the critical consumption of "1 liter per 1000 km". About half a year or a year of such a ride and a burnout / broken jumper ... There are other scenarios, but these are particulars.

A specific example, of which there are quite a few, is a whole epidemic (google "piston burned out"):
https://www.drive2.ru/l/288230376152314746/ - classic, which should be included in the textbook in the future.

7. How can I personally protect myself?
Decoke the engine in time, and (or) use it from the very beginning of operation, as well as change the oil no later than (!) 400 hours (better before, about which). If the piston is of modern size and the engine is highly boosted (these are engines with a volume of up to 2 liters and the smaller, the worse), then the rings will anyway, one way or another, someday sit down from the temperature. But you have every chance to extend their life by 2-3 times, even if it’s completely against the physical parameters of the piston and you can’t trample ...

P.S. A drop of positive: such motors relatively cheap to repair, if only because they have few cylinders.

Each piston in your vehicle's engine has two separate compression rings on the piston head and an oil scraper ring assembly on the piston skirt. The rings roll in the annular grooves inside the piston. Compression rings contain pressure from expanding gases inside the combustion chamber, helping to utilize the energy generated while preventing blow-by gases from entering the crankcase. The oil scraper scrapes excess oil from the cylinder walls ahead of the compression rings to prevent oil from entering the combustion chamber. Failure of any of these rings will result in loss of performance if there are other problems and symptoms.

Broken compression rings

The result of broken compression rings will immediately reveal itself in the form of loss of power, rough idle and possibly malfunction of the damaged cylinder. Insufficient flue gas containment will cause blow-by gases to enter the engine crankcase and be forced out through the crankcase ventilation system. The crankcase ventilation valve is most likely located on the valve cover. Disconnect the exhaust tube from the crankcase ventilation valve, and if you notice a strong smell or smoke coming out of the valve, then there is a good chance that the compression rings are broken.

In addition to the obvious problems in engine performance, other problems can develop over time. For example, a diesel engine running on high sulfur marine or agricultural fuels can be severely damaged due to loss of compression. Partially burned fuel hits the rings, and the sulfur in the fuel mixes with the water present in the oil, resulting in a chemical reaction that turns into sulfuric acid, which damages the internal components of the engine.

In gasoline engines, the fuel acts as a solvent, thinning the oil and helping protect internal parts. Check compression with a tester. Typically, compression should be around 11-12 bar with no more than 15% difference between cylinders. If the compression on one of the cylinders is less than these values, then most likely the ring is broken on it.

Broken oil ring

A broken oil scraper ring assembly can be recognized by the quality of the exhaust gases, which turn blue in color and have a distinct oil smell. Exhaust gases are emitted in the form of puffs of blue smoke during the cycle of operation of a damaged cylinder, and exhaust of a normal type is emitted in the cycle of operation of serviceable cylinders. These jerky clubs allow for easy visual diagnosis. Other symptoms include oil loss in the absence of leaks, as well as oil deposits on the spark plug of an inoperative cylinder.

Mechanical damage

In addition to the damage caused by blow-by gases, improper lubrication and free hydrocarbons contained in the oil, there are obvious mechanical damages. The edges of the rings can push against the cylinder walls, preventing other rings from making good contact with the cylinder walls, and exacerbate symptoms. The annular groove in the piston can be damaged, and since the cylinder walls and rings are harder than an aluminum piston, the piston itself can be damaged or partially destroyed, resulting in more serious damage.

Since any particles settle on the bottom of the engine crankcase, causing possible more damage, broken rings should be replaced immediately. You can remove the cylinder block cover to inspect damaged cylinder walls, or use a mechanical chamber passed through the spark plug hole. This will be the least invasive procedure.

Causes of broken rings

Since the rings were properly sized and installed during engine assembly, any damage to the rings was likely caused by other mechanical problems. When the engine overheats, the piston expands, reducing the gap between the piston and the cylinder. This reduced clearance can lead to metal transfer from the piston to the cylinder, or so-called galling.

Carried aluminum can collect on the cylinder wall and cause leakage or breakage of the top compression ring. Oil scraper rings can break if there is an increased gap between the piston and the cylinder, causing too much piston popping. The piston skirt (and in fact the cylinder machines themselves) can be damaged, and this, in turn, can destroy the oil scraper ring assembly.

Piston- one of the main elements of the internal combustion engine. It converts the energy of the burnt gases into mechanical energy. The working conditions of the piston are extremely unfavorable. It is subject to mechanical loads from gas pressure and inertial forces, high thermal loads during periods of direct contact with hot gases during fuel combustion and expansion of combustion products. Additionally, the piston heats up from friction against the cylinder walls.

The pistons of internal combustion engines must have sufficient strength, rigidity with a small mass (to reduce inertia forces), high thermal conductivity and wear resistance. In modern engines, pistons made of aluminum alloys are most widely used. Such materials meet the requirements for pistons in most of their parameters. But one of the disadvantages of aluminum alloys is their low thermal stability (an increase in temperature to 300 ° C leads to a decrease in the mechanical strength of aluminum by 50-55%)

From the figures below, it can be seen that the heating temperature of the piston surface is unevenly distributed both in the cross section (Fig. 1) and in the circumferential (Fig. 2).

Rice #1 Rice #2

The temperature level at individual points of the piston approaches critical values. And it is not surprising that in the event of a malfunction in the engine, such conditions may occur under which, at certain points of the piston, the metal is not able to withstand high temperatures, and we are faced with a phenomenon called “Piston Burnout”. Sometimes "failures" are man-made. For example, boosting the engine in terms of power can result in burnout of the pistons as a side result.

From the foregoing, the conclusion suggests itself - the engine has overheated - get a burnout of the piston, but practice does not confirm this. Here the explanation can be simple: it takes time for the piston to burn out, but during this time the engine manages to fail for other reasons - piston head scuffing, rings sticking. That is, it is possible to fix the phenomenon of “piston burnout” in the engine in its pure form when this defect develops mainly without accompanying defects (usually scuffing). This happens when the engine overheats locally. When, at certain moments of engine operation, temperatures can rise excessively without a significant change in the overall thermal stress of the engine. These are failures in the processes occurring in the combustion chambers of engines.

The combustion process involves fuel and oxygen in the air. Consider each of the components of the combustion process.

Fuel. Fuel can directly affect engine overheating - low-quality low-octane fuel leads to engine detonation and indirectly, through fuel equipment - poor-quality fuel atomization as a result of fuel supply equipment malfunctions, the use of non-standard nozzles.

Detonation occurs in engines with external mixture formation (gasoline). In this process, the entire volume of the fuel mixture simultaneously enters into the reaction (during normal combustion, the flame front propagates from the spark plug). The pressure and temperature rise sharply. At the same time, the value of these parameters significantly exceeds the normal operating values. In view of the transience of the process, the surfaces in contact with hot gases are overheated (heat does not have time to be removed). High pressure in the combustion chamber contributes to the intensification of gas breakthrough through seals (piston rings) and leaks (in valves). In combination with high temperature, the escaping gases simply wash out the metal with the formation of characteristic wear marks (Photo.1)

Photo #1 The destruction of the Mazda piston as a result of detonation. A trace of the metal being washed out by the flow of the erupting gas is clearly visible.

Malfunctions of the fuel equipment can lead to a disruption in the course of the combustion process, as a result of which the combustion of the fuel is extended in time. Such phenomena can be observed on engines with internal mixture formation (diesel engines). Poor atomization of fuel, fuel getting on the piston (for those processes where this is not provided) leads to overheating of the piston bottom, melting, burning (Photo. 2).

Air- the second component of the combustion process.

The lack of oxygen in the air leads to a change in the combustion process. The combustion process is stretched over time (this applies to engines with internal mixture formation). Further, the process develops similarly to the process with low-quality fuel atomization. The reasons for the lack of air are untimely maintenance of air filters (especially when working in conditions of increased dustiness), malfunctions of the boost unit (turbocharger, supercharger) if one is installed on the engine.

Photo #2 HOWO car piston. Melting of the piston bottom.

A large amount of dust was found in the engine, non-standard sprayers were used.

Piston burnout usually occurs in areas of maximum temperatures (edges of the combustion chamber, exhaust valve area). Figure 2 shows the characteristic temperature distribution over the surface of the piston bottom. Burnout is less likely to occur on the first and last pistons of the engine, since their thermal state is not as stressed as that of pistons located in the middle of the engine.

Summary - Many factors affect the operation of the piston and it is impossible to give an unequivocal answer whether a particular piston will burn out or some other defect will occur. You can estimate the probability of an event occurring. And in order to prevent the onset of such an unpleasant event as burnout of the piston, it is necessary to follow the rules recorded in the OM. After all, piston burnout is a purely operational defect.

Why did the piston burn out?

Why did the piston burn out?

ALEXANDER KHRULEV, Candidate of Technical Sciences

By themselves, defects in the mechanical part of the engine, as you know, do not appear. Practice shows: there are always reasons for damage and failure of certain parts. It is not easy to understand them, especially when the components of the piston group are damaged.

The piston group is a traditional source of trouble for the driver operating the car and the mechanic repairing it. Overheating of the engine, negligence in repairs - and please - increased oil consumption, blue smoke, knocking.

When "opening" such a motor, scuffs on pistons, rings and cylinders are inevitably found. The conclusion is disappointing - expensive repairs are required. And the question arises: what was the fault of the engine, that it was brought to such a state?

It's not the engine's fault, of course. It is simply necessary to foresee what these or those interventions in its work lead to. After all, the piston group of a modern engine is “thin matter” in every sense. The combination of the minimum dimensions of parts with micron tolerances and the enormous forces of gas pressure and inertia acting on them contributes to the appearance and development of defects, ultimately leading to engine failure.

In many cases, simply replacing damaged parts is not the best engine repair technique. The reason for the appearance of the defect remained, and if so, then its repetition is inevitable.

To prevent this from happening, a competent minder, like a grandmaster, needs to think several moves ahead, calculating the possible consequences of his actions. But this is not enough - it is necessary to find out why the defect occurred. And here, without knowledge of the design, operating conditions of parts and processes occurring in the engine, as they say, there is nothing to do. Therefore, before analyzing the causes of specific defects and breakdowns, it would be nice to know ...

How does a piston work?

The piston of a modern engine is a seemingly simple detail, but it is extremely responsible and complex at the same time. Its design embodies the experience of many generations of developers.

And to some extent, the piston forms the appearance of the entire engine. In one of the previous publications, we even expressed such an idea, paraphrasing a well-known aphorism: “Show me a piston, and I will tell you what kind of engine you have.”

So, with the help of a piston in the engine, several problems are solved. The first and main thing is to perceive the pressure of the gases in the cylinder and transfer the resulting pressure force through the piston pin to the connecting rod. This force is then converted by the crankshaft into engine torque.

It is impossible to solve the problem of converting gas pressure into torque without reliable sealing of the moving piston in the cylinder. Otherwise, a breakthrough of gases into the engine crankcase and oil from the crankcase into the combustion chamber are inevitable.

To do this, a sealing belt with grooves is organized on the piston, in which compression and oil scraper rings of a special profile are installed. In addition, special holes are made in the piston to discharge oil.

But this is not enough. During operation, the bottom of the piston (fire zone), in direct contact with hot gases, heats up, and this heat must be removed. In most engines, the cooling problem is solved using the same piston rings - heat is transferred through them from the bottom to the cylinder wall and then to the coolant. However, in some of the most loaded designs, additional oil cooling of the pistons is done, supplying oil from below to the bottom using special nozzles. Sometimes internal cooling is also used - the nozzle supplies oil to the internal annular cavity of the piston.

For reliable sealing of cavities from the penetration of gases and oils, the piston must be held in the cylinder so that its vertical axis coincides with the axis of the cylinder. All sorts of distortions and "shifts" that cause the "hanging" of the piston in the cylinder, adversely affect the sealing and heat transfer properties of the rings, increase the noise of the engine.

The piston skirt is designed to hold the piston in this position. The requirements for the skirt are very contradictory, namely: it is necessary to provide a minimum, but guaranteed, clearance between the piston and the cylinder both in a cold and in a fully warmed up engine.

The task of designing a skirt is complicated by the fact that the temperature coefficients of expansion of the materials of the cylinder and piston are different. Not only are they made of different metals, their heating temperatures vary many times over.

To prevent the heated piston from jamming, modern engines take measures to compensate for its thermal expansion.

First, in the cross section, the piston skirt is shaped like an ellipse, the major axis of which is perpendicular to the axis of the pin, and in the longitudinal section, it is a cone, tapering towards the bottom of the piston. This shape allows the skirt of the heated piston to conform to the cylinder wall, preventing jamming.

Secondly, in some cases, steel plates are poured into the piston skirt. When heated, they expand more slowly and limit the expansion of the entire skirt.

The use of light aluminum alloys for the manufacture of pistons is not a whim of designers. At high speeds, typical for modern engines, it is very important to ensure a low mass of moving parts. Under such conditions, a heavy piston will require a powerful connecting rod, a “mighty” crankshaft and an overly heavy block with thick walls. Therefore, there is no alternative to aluminum yet, and you have to go to all sorts of tricks with the shape of the piston.

There may be other "tricks" in the piston design. One of them is a reverse cone at the bottom of the skirt, designed to reduce noise due to the “relaying” of the piston in dead spots. To improve the lubrication of the skirt, a special microprofile on the working surface helps - microgrooves with a pitch of 0.0.5 mm, and a special anti-friction coating helps to reduce friction. The profile of the sealing and fire belts is also defined - here is the highest temperature, and the gap between the piston and the cylinder in this place should not be large (there is an increased likelihood of gas breakthrough, the risk of overheating and breakage of the rings) or small (there is a high risk of jamming). Often, the resistance of the fire belt is increased by anodizing.

All that we have said is far from a complete list of requirements for a piston. The reliability of its operation also depends on the parts associated with it: piston rings (dimensions, shape, material, elasticity, coating), piston pin (clearance in the piston bore, method of fixation), cylinder surface condition (deviations from cylindricity, microprofile). But it is already becoming clear that any, even not too significant, deviation in the operating conditions of the piston group quickly leads to defects, breakdowns and engine failure. In order to repair the engine in the future with high quality, it is necessary not only to know how the piston is arranged and works, but also to be able to determine by the nature of the damage to the parts why, for example, a scuff has occurred or ...

Why did the piston burn out?

An analysis of various piston damages shows that all causes of defects and breakdowns are divided into four groups: cooling failure, lack of lubrication, excessively high thermal and force effects from gases in the combustion chamber, and mechanical problems.

At the same time, many causes of piston defects are interrelated, as are the functions performed by its various elements. For example, defects in the sealing belt cause overheating of the piston, damage to the fire and guide belts, and scuffing on the guide belt leads to a violation of the sealing and heat transfer properties of the piston rings.

Ultimately, this can cause burnout of the fire belt.

We also note that with almost all malfunctions of the piston group, increased oil consumption occurs. With severe damage, thick, bluish exhaust smoke, a drop in power and difficult starting due to low compression are observed. In some cases, the knock of a damaged piston is heard, especially on a cold engine (for more details on piston knock, see Nos. 8.9/2000).

Sometimes the nature of the defect in the piston group can be determined even without disassembling the engine according to the above external signs. But more often than not, such an “indiscriminate” diagnosis is inaccurate, since different causes often give almost the same result. Therefore, the possible causes of defects require a detailed analysis.

Violation of piston cooling is perhaps the most common cause of defects. This usually occurs when the engine cooling system malfunctions (chain: “radiator - fan - fan switch on sensor - water pump”) or due to damage to the cylinder head gasket. In any case, as soon as the cylinder wall ceases to be washed from the outside by liquid, its temperature, and with it the temperature of the piston, begin to rise. The piston expands faster than the cylinder, moreover, unevenly, and eventually the clearance in certain places of the skirt (usually near the pin hole) becomes equal to zero. Seizure begins - the seizure and mutual transfer of materials of the piston and cylinder mirror, and with further engine operation, the piston jams.

After cooling, the shape of the piston rarely returns to normal: the skirt is deformed, i.e. compressed along the major axis of the ellipse. Further operation of such a piston is accompanied by knocking and increased oil consumption.

In some cases, the piston burr extends into the sealing belt, rolling the rings into the piston grooves. Then the cylinder, as a rule, turns off from work (compression is too low), and it is generally difficult to talk about oil consumption, since it will simply fly out of the exhaust pipe.

Insufficient piston lubrication is most often characteristic of starting conditions, especially at low temperatures. Under such conditions, the fuel entering the cylinder washes away the oil from the cylinder walls, and scoring occurs, which are usually located in the middle part of the skirt, on its loaded side.

Double-sided scuffing of the skirt usually occurs during prolonged operation in the oil starvation mode associated with malfunctions of the engine lubrication system, when the amount of oil falling on the cylinder walls decreases sharply.

The lack of lubrication of the piston pin is the reason for its jamming in the holes of the piston bosses. This phenomenon is typical only for designs with a pin pressed into the upper head of the connecting rod. This is facilitated by a small gap in the connection between the pin and the piston, so the "sticking" of the fingers is more often observed in relatively new engines.

Excessively high thermal force effect on the piston from hot gases in the combustion chamber is a common cause of defects and breakdowns. Thus, detonation leads to the destruction of the bridges between the rings, and glow ignition leads to burnouts (for more details, see Nos. 4, 5/2000).

In diesel engines, an excessively large fuel injection advance angle causes a very rapid increase in pressure in the cylinders (“rigidity” of work), which can also cause breakage of the jumpers. The same result is possible when using various fluids that make it easier to start a diesel engine.

The bottom and fire belt can be damaged if the temperature in the diesel combustion chamber is too high, caused by a malfunction of the injector nozzles. A similar picture also occurs when the piston cooling is disturbed - for example, when the nozzles supplying oil to the piston, which has an annular internal cooling cavity, coke. Seizure that occurs on the top of the piston can also spread to the skirt, trapping the piston rings.

Mechanical problems, perhaps, give the largest variety of piston group defects and their causes. For example, abrasive wear of parts is possible both “from above”, due to dust entering through a torn air filter, and “from below”, when abrasive particles circulate in the oil. In the first case, the cylinders in their upper part and the compression piston rings are the most worn, and in the second case, the oil scraper rings and the piston skirt. By the way, abrasive particles in the oil can appear not so much from untimely maintenance of the engine, but as a result of the rapid wear of any parts (for example, camshafts, pushers, etc.).

Rarely, piston erosion occurs at the “floating” pin hole when the retaining ring pops out. The most likely reasons for this phenomenon are the non-parallelism of the lower and upper heads of the connecting rod, which leads to significant axial loads on the pin and the “knocking out” of the retaining ring from the groove, as well as the use of old (lost elasticity) retaining rings when repairing. The cylinder in such cases turns out to be damaged by a finger so much that it can no longer be repaired by traditional methods (boring and honing).

Sometimes foreign objects can get into the cylinder. This most often occurs with careless work during engine maintenance or repair. A nut or bolt, caught between the piston and the head of the block, is capable of many things, including simply “failing” the piston bottom.

The story about defects and breakdowns of pistons can be continued for a very long time. But what has already been said is enough to draw some conclusions. At least you can already tell...

How to avoid burnout?

The rules are very simple and follow from the features of the piston group and the causes of defects. However, many drivers and mechanics forget about them, as they say, with all the ensuing consequences.

Although this is obvious, it is still necessary during operation: to keep the power supply, lubrication and cooling systems of the engine in good condition, to service them in time, not to overload a cold engine, to avoid the use of low-quality fuel, oil and inappropriate filters and spark plugs. And if something is wrong with the engine, do not bring it "to the handle", when the repair will no longer cost "little blood".

When repairing, it is necessary to add and strictly follow a few more rules. The main thing, in our opinion, is that one should not strive to ensure minimum piston clearances in the cylinders and in the locks of the rings. The epidemic of "small gap disease", which once struck many mechanics, is still not over. Moreover, practice has shown that attempts to "tighter" install the piston in the cylinder in the hope of reducing engine noise and increasing its resource almost always end in the opposite: piston scuffing, knocking, oil consumption and repeated repairs. The rule “better clearance is 0.03 mm more than 0.01 mm less” always works for any engine.

The rest of the rules are traditional: high-quality spare parts, proper processing of worn parts, thorough washing and careful assembly with mandatory control at all stages.

	Seizures on the skirt can result from insufficient clearance or overheating. In the latter case, they are located closer to the finger hole.
	Insufficient lubrication caused one-sided scuffing of the skirt (a). With further work in this mode, the tear extends to both sides of the skirt (b).
	Seizure of the finger in the hole of the piston bosses occurred immediately after starting the engine. The reason is a small gap in the connection and insufficient lubrication.
	The occurrence of rings in the grooves and scoring as a result of too high a temperature in the combustion chamber (a). With insufficient cooling of the bottom, the seizure extends to the entire upper part of the piston (b)
	Poor oil filtration caused abrasive wear on the skirt, cylinders and piston rings.
	A warped connecting rod usually results in an asymmetrical contact patch between the skirt and the cylinder due to misalignment of the piston.

The zone of the bottom and the top zone is completely destroyed. The hot zone burned out to the reinforcing insert. The molten piston material has moved along the piston skirt and caused damage and scuffing there as well. The reinforcing insert of the first compression ring is partially preserved only on the left side of the piston.

The rest of the reinforcing insert detached from the piston during operation and caused other damage in the combustion chamber. Parts of the piston flew off with such force that they fell through the intake valve into the intake manifold and thus also into the adjacent cylinder and caused damage there (impact marks).

to fig. 2: in the direction of injection by one or more jets of nozzles, erosive burnouts appeared on the piston bottom and on the edge of the heat zone. The piston skirt and piston ring area are free of burrs.

Damage assessment

Damage of this kind occurs especially in direct injection diesel engines. This applies to pre-chamber diesel engines only if one of the pre-chambers is damaged and, as a result, the pre-chamber engine turns into a direct injection engine.

If the injector of the corresponding cylinder does not maintain injection pressure after the end of the injection process and the pressure drops, vibrations in the high pressure fuel line can once again raise the injector needle, so that after the end of the injection process, fuel is injected again into the combustion chamber (mechanical injectors).

If the oxygen in the combustion chamber is exhausted, then individual drops of fuel flow through the entire combustion chamber and fall on the bottom of the piston moving down closer to the edge. They quickly burn out there with a lack of oxygen, and quite a lot of heat is generated. At the same time, the material in these places softens. The dynamic forces and erosion of the fast-flowing combustion gases pull out individual particles from the surface or remove the head completely, resulting in damage.

Possible causes of damage

1. Leaky nozzles or hard moving or stuck nozzle needles.
2. broken or weakened injector springs.
3. defective pressure reducing valves in the high pressure fuel pump injection quantity and injection timing not adjusted according to the engine manufacturer's instructions.
4. in prechamber engines: a defect in the prechamber, but only in combination with one of the above reasons.
5. ignition delay due to insufficient compression as a result of too much clearance, incorrect valve timing or leaking valves
6. too long delay due to non-flammable diesel fuel (too low cetane number)