How to check the cylinder head for microcracks. Microcrack detection. Before disassembling the cylinder head

Deformations of key elements of the engine, such as the cylinder block and cylinder head, are serious malfunctions that, if not corrected in a timely manner, can lead to the need for an overhaul of the engine. Cracking in the engine block and cylinder head is one of the most difficult car breakdowns. Cracks can occur due to impact (for example, in an accident), due to high wear or manufacturing defects. In this article, we will consider how to determine that the engine block or cylinder head is cracked, and what can be done about it.

Table of contents:

Symptoms of a crack in the cylinder block and cylinder head

There are several signs, upon detection of which it is worth sounding the alarm and sending the engine for diagnostics. They can indicate both the formation of cracks in the engine and other malfunctions. Most often, cracks in the cylinder block and cylinder head are indicated by:

Regular. If, due to a crack, the system is no longer tight, this will lead to a leak of coolant and constant overheating of the engine. Also, such a problem may arise due to burnout or other defects;
Problems with the temperature control device (thermocouple). This is fraught with severe engine overheating and deformation;
The pressure in the expansion tank does not hold and air locks form;
Incorrect indicators. If the arrow of the temperature sensor changes chaotically, then up, then down, this may indicate sharp jumps in the temperature of the engine itself during operation;
Engine vibration. One of the most obvious signs of a cracked cylinder block. If the engine vibrates excessively or “troit”, especially when driving uphill, this could indicate the presence of microcracks in the engine block.

How to find cracks in a block of cylinders

Far from always, when it comes to a crack in a cylinder block, a serious defect visible to the eye is meant. Quite often these are microcracks, which can be determined by one of the following methods:

Pneumatic crimping;
The use of ultrasound scanning;
Application of specialized magnetically sensitive equipment;
Hydrocontrol.

Each of these methods allows you to establish whether there are microcracks in the cylinder block, and where they are located. Most often, in service centers in the absence of specialized equipment for diagnosing the cylinder block, they use the method of finding a crack using water or air.

The essence of this method is simple - water is pumped into the cylinder block, and if it seeps, then there is a crack in this place. When using air, air is pumped in, and the part itself is submerged under water, thereby, by the presence of bubbles on the surface of the water, it will be possible to understand whether there is a crack.

Note: Magnets can be used to pinpoint the crack location. They are installed along the edges of the alleged split of the cylinder block, after which the space between them is filled with conductive sawdust. If there is a crack, the magnetic field lines will break and sawdust will collect in the place where the microcrack is.

How to repair a crack in a block of cylinders

Depending on the extent of the damage, different methods of repairing the cylinder block can be used. It should be noted that in some cases it is more expedient to replace the unit, rather than repair it.

Welding method

The most common way to repair a crack in a block of cylinders. At the same time, welding a cylinder block is a rather difficult job, since it implies strict adherence to technological regulations. If welding mistakes are made, the seam will open as the engine is running and the problem will return.

During welding, the ends of the crack are initially drilled into the cylinder block. This must be done to avoid the possibility of crack propagation. Drilling and further grinding are carried out at an angle of 90 degrees.

Next, the welding process itself begins. To do this, the cylinder block must be heated to 650 degrees Celsius, after which a continuous seam is applied with the help of a filler cast iron-copper rod and flux. Further, the part is gradually cooled in a heating cabinet.

Important: Do not cool down the part sharply, otherwise it will lead to rupture of the seam.

It is worth noting that it is possible to weld the cylinder block without heating it. To do this, it is worth using electric welding and copper electrodes in a tin wrapper. At the end of the work, the superimposed seam must be degreased with acetone or special compounds. On top of the seam, then you need to apply a layer of epoxy paste with a spatula. Next, the part must be “dried” by leaving it at room temperature for 24 hours to allow the epoxy to dry completely. The final stage is grinding the processed seam.

By applying epoxy and fiberglass

A simple method that allows you to eliminate minor cracks on the surface of the cylinder block. The method involves the creation of an additional layer on the surface of the crack, made of epoxy paste and fiberglass.

To seal the crack in this way, you first need to degrease the surface well, so that the applied compounds "take root" better. Next, several layers of epoxy paste and several layers of fiberglass are alternately applied. The last layer should be epoxy.

SEAL-LOCK method

Quite a laborious modern way to eliminate cracks in the cylinder block. Its clear advantage is the ability to carry out work without welding and without dismantling the engine itself. The essence of the method is to fill the existing cracks with soft metal.

The work is done as follows:

Unlike the seam weld repair method, the SEAL-LOCK method provides a more reliable seam that is not susceptible to temperature changes.

Regardless of which metal alloy is used in the manufacture of the block, over time, during operation, a crack can form in the engine block.

Visually it is possible to identify deep breaks, but microcracks cannot be identified "by eye".

Likely symptoms and causes

The following are signs by which you can indirectly determine a crack in a block or head. Although, the described symptoms may indicate other malfunctions.

Overheating of the engine, antifreeze completely flows out of the system. If there is no question about the tightness of the cooling system itself, in this case it is necessary to check how well the cylinder head bolts are tightened. Important: Be careful, they may break when pulling the bolts.
Incorrect operation of the temperature control device (thermocouple), due to overheating, the cylinder head is deformed.
Faulty expansion tank plug, in which the valve does not hold pressure, air locks are formed.
In warm weather, the engine temperature fluctuates. The arrow of the temperature sensor makes sharp jumps in the direction of increasing or decreasing temperatures.
Vibration of the engine or "triplet" is especially noticeable when going uphill. As practice shows, this is one of the most common symptoms of the formation of microcracks. Important: to confirm the presence of microcracks on the cylinder block or to make sure that there is a crack in the cylinder head, unscrew the spark plug. If the candle is wet, try the liquid on your tongue. The sweet taste means that it is antifreeze that gets into the oil through a micro crack. Add coolant and start the engine without closing the hood and expansion tank cap. If the liquid starts to boil immediately, this is a sure sign of a crack in the cylinder head.
Cracks are likely to occur near the guide bushing or intake valve bushing. In this case, the head will have to be changed.
Gases go away. To determine the leak, you can put on a rubber medical glove on the expansion tank, or the neck of the radiator, and secure with a rubber band. If the glove inflates, then there is a problem.

It is better to use imported and silicate-free G-11 antifreeze for aluminum blocks. For cast iron cylinder blocks, it is better to use standard red antifreeze. It is designed for a temperature of -80 +135.

Note: cracks may appear on the upper plane of the cylinder block due to poor flushing and purging of the block before assembly. This leaves dirt and fluid in the threaded bolt holes.

Determination methods

To finally make sure that microcracks are formed, there are several ways to identify defects.

The magnets are installed on the body of the device or the cylinder head. Metal shavings are poured on top. It begins to move to the places where the magnets are installed, hammering into cracks.
On the cylinder head surface thoroughly washed with acetone or kerosene, apply a special liquid paint and wait 10 minutes. After that, wipe off the remaining paint with a clean rag. Defects after this method are detected immediately.
Liquid can be used to check the integrity. To do this, it is necessary to tightly close all openings and pour water into the channel. Using a pump, we pump air into the channel at a pressure of 0.7 MPa. We leave the block in this state for several hours. Leaving water will indicate that there are defects in the block head. In the same way, the integrity is checked by immersing the unit in a container of water. In this case, bubbles will show where the cracks are.

Locations of defects, for the elimination of which it is not worth undertaking.

on valve seats;
on the cylinder mirrors;
on the plane of contact between the block and the head.

How to repair damaged areas

Sealing with electric welding

Drill the cracks with a drill so that they do not go further and do not begin to grow during operation. Grind.

We heat the block up to 600-650 degrees. For sealing, we use a filler rod made of a cast-iron-copper alloy with a diameter of 5 mm and a flux. Protect the seam from oxidation with borax.

An even layer with a protrusion of no more than 2 mm should remain on the surface in the engine block. After that, we cool the unit in a heating cabinet.

Arc welding

In this case, heating of the block is not required. Electronic wire is used as filler material. Argon is used as a welding medium. Do not overheat over 60 degrees.

Sealing cylinder head cracks

We heat the head to a temperature of 200 degrees. We use an acetylene torch for this. The sealing is done using direct current. The diameter of the electrode is selected depending on the width and thickness of the wall.

We select a piece of metal the size of a crack. We wrap the copper alloy electrodes with a tin can and weld the patch. Sand and finish with epoxy paste.

Application of epoxy paste

Cut the fracture by grinding and drill the ends of the cracks with a drill, no more than 85 mm in diameter. Insert copper plugs into the holes. We traverse the outlines of the cracks with a notch to create an artificial roughness.

We degrease the surface using acetone, heat it with an infrared lamp to a temperature of 80 degrees. Apply epoxy paste to the fault in the following sequence:

1 layer 1 mm,
second 2-3 mm,
the third is 3-4 mm.

Withstand for 24 hours at a temperature of 20 degrees, then it is necessary to dry the place of repair in a drying chamber, at a temperature of 90 degrees, for one hour.

After drying, clean the bonded area and level with sanding.

A microcrack in the cylinder is probably the biggest headache for both the owner of the car and the craftsman he turns to. The thing is that you cannot see it visually, and the symptoms are that the gasket under the head begins to burn out. Several times I came across such engines. But there is also a microcrack in the head. The symptom of microcracks in the cylinder and the head is the same as the beginning burnout of the gasket under the head.

I'll tell you first about a microcrack in the head, and below about a microcrack in the cylinder.

A guy drove up in a VAZ-2106 and said the car was boiling all the time, waited a little until the engine stopped boiling, opened the radiator cap and added coolant to the radiator, started the engine at idle. I began to look into the radiator, I see how bubbles come out of the radiator, (but if liquid was added to the radiator, then usually several bubbles immediately pop up, but they quickly stop), in front-wheel drive cars, the tank begins to inflate into which coolant is poured and bubbles also appear. If the gasket under the head is burned out badly, then the liquid goes into the cylinder, the liquid seeps through the piston into the engine block and enters the oil, a sign that the oil becomes the color of a white emulsion and increases in volume.

I immediately determined that the gasket was starting to burn out, I removed the head and the gasket was new (completely fresh) and there was no hint of burnout, I asked if they had already changed the gasket, said two days ago I bought the head from my hands, replaced it and has been boiling ever since. I ask, but before that it was boiling on the old head, he says, it wasn’t boiling, but it was Troilus due to valve burnout, I decided to buy this head, all the more it was not expensive, so that it wouldn’t suffer with it. I say you have two options, buy another head, or take the old one, I'll fix it, he decided to repair the old one (the head was really badly worn out, all the valves and valve guides had to be changed). I put the repaired head and the boiling stopped. But what's funny is that after a while another guy drove up to me in a VAZ-2107 and also complained that the engine was boiling, opened the hood and recognized the head because of which the six was boiling (there was a spot with red paint on it, that's why I remembered it). I asked him for a long time changed the head, he says, the other day. I told him the story of this head. Visually, I did not find microcracks in this head, and I did not understand where it was.

Photo. Microcrack in the head

Most often, a microcrack in the head happens as shown in the photo, and most often in my practice it happens in the second or third cylinder. The photo shows the location of the microcrack in red. It is easier to find a microcrack, so clean the carbon deposits with a knife in the place where the crack is shown, and it appears.

Photo. Head from Niva with two microcracks at once

And once a head with two microcracks was caught at once, it is in the photo and the cracks are shown by arrows, I found them immediately, it was only necessary to remove the carbon with a knife with a knife. The sign of these microcracks in this Niva was this, the second and third cylinders of the Troilus, at low speeds, the antifreeze left and flew out through the muffler, there were also bubbles in the radiator, but the antifreeze did not go into the oil. Maybe because this engine has a very good piston group, but if there was a bad piston, then antifreeze would penetrate into the block. This remained a mystery why the antifreeze did not penetrate into the oil through the pistons, I think very little of it entered the cylinders, basically the pressure forced the air into the head and sucked the drops into the cylinders.

Microcrack in the cylinder

Signs such as a microcrack in the head, I will not repeat myself, but I will immediately be taken aback by the method of repairing such a cylinder. It is good if you can visually find such a crack, it may be a chip in the cylinder, but more often you will not see it, but it manifests itself when the engine is running and heats up to operating temperature. I ran into a microcrack when the engine was running for a long time, and suddenly a microcrack appeared, but where it is is unknown.

Photo. A crack in the cylinder is indicated by an arrow.

In the photo you see a VAZ 2106 engine block with a crack in the cylinder. And all because this block is designed for 79mm pistons, it was bored out for 82mm pistons. and seemingly badly run in, which led to this crack, the signs were such, there were constant bubbles in the expansion tank.

I came across several cars with a VAZ 2106 block boring for 82mm pistons. and, in principle, worked fine. But I do not advise doing this, since the cylinder liner becomes very thin, and there is a great possibility of such a crack formation.

Photo. A head with three cracks, note that this head was milled on a machine, but such milling is unacceptable, since very deep irregularities remain, they are immediately pressed by the metal part of the gasket, which contributes to the rapid burnout of the gasket. The head must be absolutely smooth when milling.

I had to sleeve this block and put 79mm pistons. the engine worked like new.

I always warn the owner of the car after I remove the head and do not find burnout in the gasket and cracks in the head or block, which can be for two reasons, and I give him the choice of where to start first, replace the head or we will sleeve the block.

The main thing is that the borer who bores the cylinders and cuts the block is a professional in his field. A good borer can bore well even an obvious crack in the cylinder. Therefore, immediately warn the borer that there is a microcrack in some cylinder (I do not know the subtleties of how the cylinders are liner), but several such engine blocks have been running after the liner for several years and everything is fine.

Usually, the owner of the car chooses to start with plugging the block, and if it does not help, then of course you will have to change the head.

I know one ninety-ninth, which drives with such a microcrack, the driver simply twists the plug on the expansion tank slightly so that it does not blow up, and it does not boil.

What is the reason for the formation of permanent air jams in the VAZ injector engine?

It happens like this, the engine is started, it works fine, but after a while coolant begins to flow from under the plug of the expansion tank. You might think that the reason is a microcrack in the gasket, head, or cylinder of the engine, but there are no bubbles in the expansion tank during warming up. Usually the plug of the expansion tank is to blame for this, the valve does not hold the pressure in it, if it is replaced with a new one, everything stops.

Interestingly, I saw cars that drove even without plugs in the expansion tank, but did not boil, while others begin to boil and form air plugs due to a bad valve in the expansion tank cap. This is a mystery to me.

Crack in the block of cylinders VAZ 21083. Video

Gorobinsky S.V.

The cylinder head gasket is responsible for the tightness of the connection. The specified gasket allows to realize the sealing of the combustion chamber and the channels of the cooling jacket, through which the coolant moves. The gasket can be made of thin metal. The second available option is reinforced paronite, which additionally has a metal edging in those places where holes for the combustion chamber are made in the gasket.

Burnout or breakdown of the cylinder head gasket is a serious and fairly common malfunction. The obvious answer to the question of whether it is possible to drive with a punctured cylinder head gasket is the need for urgent repairs. It should be added that with a slight loss of tightness, it is possible to move on its own in a car, but it is advisable to eliminate such a defect urgently. In the event that the cylinder head gasket is severely punctured and signs of breakdown are clearly visible, operation is prohibited.

Read in this article

The reasons for the breakdown and how to check the cylinder head gasket

The consequences for the engine can be disastrous even with a short drive in a car with this problem. If the breakdown of the cylinder head gasket is ignored, even after a small mileage, a major overhaul becomes necessary.

The specified breakdown can occur in both a gasoline and a diesel engine, in a unit with or in a variant. Breakdown of the gasket requires correct and timely diagnosis. An increase in fuel consumption, difficult engine start-up and unstable operation, a decrease in the power of the internal combustion engine, a drop in the level of coolant in the expansion tank, and low compression in the cylinders can indicate a problem at an early stage.

The most common causes of breakdown or burnout of the cylinder head gasket are:

overheating of the engine;
incorrect installation when replacing the gasket;
the consequences of the power tuning of the internal combustion engine;
inappropriate tightening torque of the cylinder head bolts;
driving on low quality gasoline, which is accompanied;

Engine overheating is the main cause of cylinder head gasket breakdown. Overheating of the motor occurs for various reasons, ranging from a malfunction and ending with such phenomena as engine detonation or. Both metal (asbestos) gaskets and paronite in such conditions usually do not withstand the rising temperature during overheating and burn out. After such a burnout, the strength of the gasket becomes less and it is blown out.

It is noteworthy that among the indirect signs of a burned-out cylinder head gasket, in a number of cases, an increase in engine temperature was noted, that is, overheating. A breakdown of the combustion chamber edging on the gasket leads to the fact that hot gases break through into the engine cooling system and overheat the antifreeze. It turns out that overheating of the motor often breaks the gasket, and then the breakdown of the gasket provokes an increase in the engine temperature.

In the list of consequences of overheating of the power unit, the curvature of the cylinder head, or rather its plane, is also noted. In everyday life, there is a definition of "the cylinder head led". Most often, it keeps the block head from overheating if the material of its manufacture is an aluminum alloy. Note that cast iron heads are more resistant to high temperatures, although cracks may occur in some cases. If the head has moved, then such a curvature is eliminated by grinding. As a preventive measure (unnecessarily), grinding the cylinder head is not recommended.

Signs of a punched cylinder head gasket

If the cylinder head gasket is burned out or it is punctured, then the list of the main symptoms of such a malfunction is marked:

gas breakthrough or drips at the junction of the head with the cylinder block;
the appearance of an emulsion in the engine lubrication system;
the engine starts to smoke with white smoke;
oil and / or exhaust gases getting into the engine cooling system;

In the event that the exhaust gases erupt in the place where the head of the block meets the cylinder block, then this is a clear sign of a punctured cylinder head gasket. This phenomenon is also accompanied by a significant increase in noise during engine operation. A noticeable release of exhaust gases to the outside through a punched gasket is not common, and it is easy to diagnose. In the event of a rupture of the outer shell of the gasket on the outer surfaces of the motor at the junction of the head and the block, drips of coolant or engine oil may also appear. Among the signs that require a more thorough examination are:

It is more difficult to diagnose a breakdown or lumbago of the cylinder head gasket if the defect is localized between the cylinders. If the cylinder head gasket is burnt out, the symptoms in this case may not appear outside, and the problem itself is accompanied only by indirect signs: fuel consumption increases, the engine is unstable and troit, and a drop in power is noted.

It should be added that in the event of a burnout of the head gasket between the combustion chambers, the exhaust gases and the fuel-air mixture in adjacent cylinders may mix. More often, a malfunction manifests itself in the form of an unstable operation of a cold motor, which returns to normal after warming up. The indicated malfunctions in the operation of the internal combustion engine can be caused by various malfunctions. As for checking the gasket, for an accurate diagnosis, it is necessary to measure the compression of the engine. If there is a similar drop in compression in adjacent cylinders, then a defect in the cylinder head gasket is quite likely.

How to change the cylinder head gasket correctly

To begin with, removing the cylinder head on some engines is a complex and time-consuming procedure that requires draining technical fluids, dismantling individual units and assemblies. When replacing the cylinder head gasket, you must make sure that the head has the most flat contact plane with the cylinder block.

No dirt, deep scratches or other defects are allowed on adjacent surfaces. If the block head was ground, then it is necessary to separately take into account the thickness of the removed layer from the adjacent surface.

It is imperative to observe the recommended sequence and force when tightening the cylinder head bolts. To obtain accurate data, the engine manufacturer and the manufacturers of cylinder head gaskets provide a diagram of how to tighten the fasteners. The recommended tightening torque (torque) is also indicated. We add that when replacing the cylinder head gasket, it is also recommended to replace the mounting bolts. After unscrewing and subsequent tightening with proper effort, the old studs do not withstand the load, as a result of which the bolt breaks.

In the event that the cylinder head stud breaks off, but the gasket is not burned out, then the broken part must be unscrewed. After that, the bolt must be replaced with a new one. To remove a broken bolt, you can use a simple method that involves welding a metal tube to the remainder of the bolt by welding. The specified tube should have a smaller diameter compared to the bolt. The tube is applied to the broken hairpin and scalded from the inside. You can also weld a nut onto the top of the tube, after which you can easily unscrew the broken hairpin without much difficulty.

Do I need to stretch the cylinder head after replacing the gasket

As mentioned above, in the process of replacing the gasket, increased attention is paid to the fastening bolts, as well as the correct tightening. The head must be tightened only with the recommended torque in a clearly defined pattern (sequence). Overtightening or insufficient tightening is not permitted.

Overtightened cylinder head bolts can cause the mounting bolt head to come off. Loss of downforce will mean that the head of the block does not fit tightly enough, there is a loss of tightness and the gasket is punched again.

As for broaching the cylinder head after replacing the gasket, it is advisable to carry out this procedure after several tens of kilometers. During this time, the driver is obliged to closely monitor the engine and its operation. The engine with a new gasket must work stably in all modes, the exhaust must be clean, the operating temperature of the engine must not exceed the permissible value.

The head must be stretched out in the event that streaks are noticed in the area of \ u200b \ u200bthe joint with the cylinder block. To do this, you need to use a torque wrench and tighten with the torque recommended by the car manufacturer to pull the head on a specific engine.

Metal or paronite cylinder head gasket: which is better

Many motorists are wondering which cylinder head gasket is better, metal or paronite. According to experts and auto mechanics, a metal cylinder head gasket can withstand heavy loads compared to a reinforced paronite gasket. This is especially true of turbocharged engines and, on which the paronite cylinder head gaskets are quickly blown out after installation.

If the engine is naturally aspirated, it is in stock configuration and its tuning is not planned, then a metal-paronite gasket becomes a quite suitable option. Moreover, the indisputable advantage of such a gasket is the ability to slightly smooth out minor nuances and irregularities of the adjacent surface.

It should also be added that between the groups of holes in the gaskets, the walls are very thin. For this reason, the service life of metal or paronite gaskets is primarily affected by the correctness and accuracy during installation, and only then the material of manufacture. The result of an incorrect installation is that the gasket quickly burns out, after replacing the cylinder head gasket, the car does not start or the knock of pistons is heard. The latter case is more typical for diesel engines.

If the diagnostics showed that the head gasket is burnt out, then further operation of the car is highly discouraged. The potential consequences for the engine and the costs of eliminating them can be ten times greater than the cost of a cylinder head gasket and the work of replacing it. For different car models, the cost of laying can be from 15 to 50 USD. Mounting bolts will cost an average of $ 10-20.

Separately, it is worth paying attention to the question of whether it is possible to reuse the cylinder head gasket. An unambiguous answer cannot be even if the gasket is in perfect condition. As practice shows, if it is necessary to remove the cylinder head, it is better to make a preventive replacement of the gasket and fasteners.

Finally, we add that increased attention must be paid to the quality of the gasket. Taking into account the complexity and volume of work on dismantling the cylinder head, it is better to immediately buy a branded original gasket or an analogue of a well-known manufacturer than to remove the head again after 10-15 thousand km. The purchase of a gasket of proper quality will be fully justified even taking into account the higher cost (by 25-50%) compared to more affordable budget options in a group of similar products.