A microcrack in the cylinder is probably the biggest headache, the owner of the car, and the master to whom he refers. The thing is that you can’t see it visually, but 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 sign of a microcrack in the cylinder and head is the same as the beginning burnout of the gasket under the head.

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

A guy drove up in a VAZ-2106 and said the car was boiling all the time, waited for a while 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 bubbles coming out of the radiator (but if you add liquid to the radiator, then usually several bubbles pop up at once, but they quickly stop), in front-wheel drive cars it starts to inflate the tank into which coolant is poured and bubbles also go. If the head gasket burns out badly, then the liquid goes into the cylinder, through the piston the liquid seeps 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, he says I bought the head from my hands two days ago, replaced it and has been boiling since then. I ask, but before that it was boiling on the old head, she says, it didn’t boil, but it was troiling due to valve burnout, I decided to buy this head, and they offered it not too expensive, so that it wouldn’t suffer with it. I say you have two options, buy another head, or bring the old one, I will fix it, he decided to repair the old one (the head was really badly stubborn, I had to change all the valves and valve guides). Put the repaired head and boiling stopped. But what's funny, 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 (it had a stain of red paint, that's why I remembered it). I asked him for a long time he 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 in what place it was.

Photo. Micro crack 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 red photo shows the location of the microcrack. It is easier to find a microcrack this way, clean the soot 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 I came across a head with two microcracks at once, it is in the photo and the cracks are shown by arrows, I found them right away, it was only necessary to remove carbon deposits with a knife. The sign of these microcracks in this Niva was such that the second and third cylinders troiled, at low speeds, the antifreeze left and flew out through the muffler, bubbles also went into 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 group, antifreeze would penetrate into the block. It remained a mystery why the antifreeze did not penetrate into the oil through the pistons, I think it entered the cylinders very little, mainly the pressure forced air into the head and completely sucked drops into the cylinders.

Microcrack in the cylinder

Signs such as a microcrack in the head will not be repeated, but I will immediately be taken aback by the method of repairing such a cylinder. Well, if you can visually find such a crack, it may be a chip in the cylinder, but more often you can’t see it, but it appears when the engine is running and heated to operating temperature. I encountered a microcrack when the engine was running for a long time, and suddenly a microcrack appeared, but where it is is unknown.

Photo. The crack in the cylinder is marked with 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 it looks like they ran in badly, which led to this crack, the signs were such that there were constant bubbles in the expansion tank.

I came across several cars with a VAZ 2106 block bore for 82mm pistons. and generally worked fine. But I do not advise you to do this, since the cylinder liner becomes very thin, and there is a high possibility of such a crack forming.

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

I had to sleeve this block, and put 79mm pistons. the engine ran 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 two reasons, and I give him a choice where to start first, replace the head or we will sleeve the block.

The main thing is that the borer that bores the cylinders and liners the block is a professional in his field. A good borer can perfectly line even an obvious crack in the cylinder. Therefore, immediately warn the borer that there is a microcrack in some cylinder (I don’t know the subtleties of how the cylinders are lined), but several of these engine blocks have been running for several years after the sleeve and everything is fine.

Usually the owner of the car chooses to start with the sleeve of the block, and if it doesn’t 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 cork slightly on the expansion tank so that it does not inflate, and it does not boil.

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

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

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

Crack in the cylinder block VAZ 21083. Video

Gorobinsky S.V.

A crack in the cylinder head occurs as a result of improper engine operation due to overheating and shear stress in the metal.

Symptoms of a crack in the cylinder head

Cracks can appear in different places, hence the different consequences. Basically, there is an opinion that when a head is pierced, white smoke comes out of the exhaust pipe, but this is only one particular case. A crack in the head can occur between different channels, respectively, and the signs of a crack in the cylinder head will be different.

Oil system- when mixing oil and antifreeze in the engine, instead of oil, an emulsion appears, a whitish foam, like a biscuit dough, and an oil film forms in the expansion tank of the cooling system.

inlet- if coolant starts to get into it, then first of all it will wash the pistons to a shine, you can look through the candle hole - the pistons will be like new. And when it enters the combustion chamber, this is just the case when white smoke can go out of the exhaust pipe, although it is not a fact that it will go.

With release channel- here the coolant will simply fly out into the pipe in the form of steam. The engine constantly releases steam and it is unlikely that anything will be noticed in this case, the liquid will simply leave the tank. Most likely, even the smell of exhaust gases in the tank will not.

with combustion chamber- through the crack, part of the liquid will go into the combustion chamber, but a very small amount, all because of the pressure difference. In the engine, when the fuel is burned, a lot of pressure is formed, and the exhaust gases through this very crack enter the cooling system, increasing the pressure in it. Because of this, the nozzles swell, and the exhaust stinks from the tank. But the liquid can also go into the combustion chamber - the cooling system is still under pressure, and the vacuum has already gone in the combustion chamber and air has begun to be sucked in. Due to the difference in pressure, the coolant begins to seep into the combustion chamber. A sign of such a crack will be clean pistons (not always), the smell in the tank, elastic pipes and a cold stove radiator (air lock).

Typical locations for cracks in the cylinder head

Car manufacturers allow cracks to form in the head, and this will not be considered a malfunction, since the crack will not be deep and will not connect the two containers. In VW diesel engines, a head with a crack between the valves is acceptable.

But finding all the cracks is a problematic task even for an experienced minder. It would seem that on the same motors, cracks should form in the same places. But that doesn't make the search any easier. There are places that can be detected with one glance at the head:

—between valves- the crack is immediately visible, passes under the saddles of two adjacent valves.

—between spark plug and valve- the same situation, again, everything is in sight and you don’t have to look anywhere

—in diesel engine crack can go from the valve towards the prechamber, such a crack is easy to see, but how to see it if it forms under the prechamber and does not go outside?

—under the valve guide- another hot spot where the crack is not visible, firstly, it is already dark in the channel, and secondly, the crack is covered with a guide bushing. Here we need a different approach, and not just a visual one. And what is the use of finding a crack between the valves, if gases do not break through it? We will not rely on chance, especially since the diagnostic method was invented a long time ago and has proven itself from the best side.

Checking the cylinder head for cracks

To check the cylinder head for cracks, it must be pressure tested, that is, all openings must be hermetically sealed and air must be blown into the channels. If you lower the head into the water, then bubbles will come out of the crack. Or vice versa - plug all the holes and pour water into the channel, then pump air into it with a pump, creating a pressure of 0.6-0.7 MPa, and let the head stand for 1 = 2 hours. If the water comes out, then the head is broken.

There are also dyes that tint water. They are very clearly visible on the crack.

And the holes in the cooling jacket are very easy to close: a rubber gasket is placed on the nickname, which is slightly larger than the hole, a metal plate is placed on top, which is screwed to the head with a bolt. And no water will pass. And to the fitting, which will protrude from the head, connect the pump and pump air. Such crimping allows you to identify all cracks.

Crack repair

Qualitatively repair the crack can only be done by welding. No adhesive composition will be able to qualitatively close a crack in the heads, because when heated to operating temperatures, the head will expand and the crack will become larger, that is, a composition is needed to close the crack, which would have the same linear thermal expansions as the head material, to also be resistant to other loads. All this can only be achieved by welding.

Preparing the Welding Head

Before welding, the crack must be cut; for this, metal is drilled along the entire length of the crack with a milling machine. The groove should turn out to be deep enough, 6-8 mm deep and approximately the same in width, it is desirable to make a wedge-shaped shape. This will help to weld the metal better. To cut a crack between saddles, you first need, and only then cut the crack.

After cutting cracks, the head must be heated to a temperature of 200-250 ° C, but not higher, so that the head does not lead. Heating allows you to reduce the stress in the metal that occurs during welding. For heating, it is best to use an acetylene torch or oven, but you can not use a blowtorch, because it can easily overheat the cylinder head.

Cylinder head welding

Gas welding with filler material can be used to weld the cylinder head, but argon arc welding (TIG) gives better results. A mass is connected to the head, and the arc burns in an argon environment between the tungsten electrode and the head, where an aluminum filler wire is slipped.

After welding, the seam must be cleaned, re-pressurized, and if everything is fine, then the surface adjacent to the block must be milled so that it is perfectly even.

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

Visually, deep gaps can be detected, but microcracks cannot be determined “by eye”.

Likely symptoms and causes

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

• Engine overheating, 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, when pulling the bolts, they may burst.
• Incorrect operation of the temperature control device (thermocouple), due to overheating, deformation of the cylinder head occurs.
• Expansion tank plug failure, in which the valve does not hold pressure, air plugs form.
• In warm weather, the engine temperature fluctuates. The arrow of the temperature sensor makes sharp jumps in the direction of increasing or decreasing temperatures.
• Engine vibration or “triple”, this is especially noticeable when climbing uphill. As practice shows, this is one of the common symptoms of the formation of microcracks. Important: to confirm the presence of microcracks on the cylinder block or to verify 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 enters the oil through a microcrack. Add coolant and start the engine without closing the hood and expansion tank cap. If the liquid immediately begins to boil, this is a sure sign of a crack in the cylinder head.
• There is a high probability of cracking near the guide bushing or inlet valve bushing. In this case, the head will have to be changed.
• The gases are leaving. To determine the leak, you can put a rubber medical glove on the expansion tank, or the radiator neck, and secure it with a rubber band. If the glove inflates, then there is a problem.

Antifreeze is better to use imported and silicate-free G-11 - for aluminum blocks. For cast iron cylinder blocks, it is better to use red standard 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. As a result, dirt and liquid remain in the threaded bolt holes.

Methods of determination

To finally verify the formation of microcracks, there are several ways to determine defects.

• Magnets are installed along the body of the device or cylinder head. Metal shavings are poured on top. She begins to move towards the installation sites of the magnets, clogging into the cracks.
• We apply a special liquid paint to the surface of the cylinder head thoroughly washed with acetone or kerosene 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 integrity. To do this, it is necessary to hermetically 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. Gone water will indicate that there are defects in the head of the block. In the same way, the integrity is checked by immersing the block in a container of water. In this case, the bubbles will show the location of the cracks.

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

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

How to repair damaged areas

Sealing by electric welding

Drill cracks with a drill so that they do not go further and begin to increase during work. Sand down.

We heat the block to 600-650 degrees. For embedding, we use a filler rod made of cast-iron-copper alloy, 5 mm in diameter, and 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 block in a heating cabinet.

Arc welding

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

Cylinder head crack sealing

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

We select a piece of metal, the size of a crack. We wrap copper electrodes from a copper alloy with a tin can and weld a patch. Sanded and finished with epoxy paste.

Application of epoxy paste

Cut the fracture by grinding and drill the ends of the cracks with a drill, with a diameter of not more than 85 mm. Insert copper plugs into the holes. We pass a notch along the outlines of the cracks to create an artificial roughness.

The surface is degreased using acetone, heated with an infrared lamp to a temperature of 80 degrees. We apply epoxy paste on the fault in the following sequence:

• 1 layer 1mm,
• second 2-3 mm,
• third 3-4 mm.

To withstand for a day 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, the glued area should be cleaned and leveled by grinding.

Checking the tightness of valves- an important event, since it largely depends on the fit of the intake and exhaust valves to the seats. Today you will know how to check the tightness of the valves, and how to grind valves at home using special probes and a set of accessories.

Without the correct and well-coordinated operation of the timing (gas distribution mechanism) - uninterrupted operation of the engine is impossible, this must be understood and all existing problems in the operation of this system should be identified in a timely manner. Play a key role in timing valve intake and exhaust, as the name already implies, some let out, while others let in ... The tightness of the valves is an important point, on which, as mentioned above, a lot depends, otherwise the necessary pressure will not be created in the combustion chamber and the operation of the internal combustion engine will be inefficient, and possibly completely impossible.

In order to perform a valve tightness test, you must have:

1. A wide locksmith's ruler or a special template;
2. Lapping paste;
3. Kerosene;
4. A special "adapt" for lapping valves.

How to check valve tightness?

Checking the tightness of the valve and the seat is carried out as follows:

1. The cylinder head (cylinder head) is removed.

2. The cylinder head and bearing housing are cleaned from dirt, carbon deposits and other oil deposits.

4. After we inspect the working surfaces of the bearing housing, camshaft bearings, as well as the walls of the mounting holes of the hydraulic pushers, they should not have any traces of metal influx or burrs.

5. The valve guides and seats must fit snugly against the "body" of the cylinder head. Seats and valves must not show cracks or burn marks.

6. Using the template, complete cylinder head flatness check, in the absence of such, this can be done using a wide locksmith line. Attach the ruler with an edge to the lower mating plane of the head diagonally, check if there is a gap between the cylinder head and the edge of the ruler. As a rule, it can be seen in the central part or along the edges. Measure the gap on both sides using a feeler gauge, the maximum allowable gap is 0.1 mm. If you get more, you will need to mill the mating plane or completely replace it.

7. Next is necessary check cylinder head tightness. To perform such a check, it is necessary to plug the supply window to the thermostat on the end surface of the block head. Then turn the head over and pour kerosene into its cooling jacket. Make sure that there are no leaks anywhere, if any are found, the cylinder head should be repaired or completely replaced.

8. Now it's the turn of the valves. To check valve tightness Put the cylinder head on a flat table with the mating plane to the top, then pour kerosene into the combustion chambers of the head and wait a couple of minutes. This procedure is also called "pouring". If you notice that the level of kerosene in the combustion chamber began to decrease, or a puddle appeared on the table, this means that one of the valves in this chamber or both valves are leaking, which means that the valves need to be lapped.

How to fix leaky valves? Lapping of valves

1. Leakage of valves is eliminated by lapping them to the seats; in the absence of cracks or damage on the plate and the valve, it can be restored by lapping. To perform this procedure, you must:

2. Remove the oil scraper cap from the valve.

3. Remove the valve that does not fit well from the guide sleeve.

5. The valve is installed in the cylinder head, and a "adapt" for lapping valves.

6. Pressing the valve against the seat, lapping is performed by rotating the valve from side to side, making 10-15 such movements, turn it 90 ° and continue lapping again. Lapping should be done until a uniform, even surface is formed on the plate and seat, and the parts themselves are perfectly adjacent to each other.

7. Upon completion, the remaining lapping paste is removed, and the valve with new valve stem seals is installed in place.

That's all for me, I wish you good luck in your work! Thank you for reading us, see you soon!

You will need

• - metal ruler
• - piece of conveyor belt - 1 m,
• - compressor,
• - a piece of organic glass - in accordance with the size of the cylinder head,
• - clamps - 4-6 pcs.

Instruction

One of the most unpleasant moments for a motorist is the phenomenon of opening an expansion tank cap, accompanied by a short-term release, not to mention its incessant extrusion when it boils for a long time, although the engine temperature has not reached a critical level. This factor clearly indicates the penetration of gases into the water jacket of the system.

In order to thoroughly find out the cause of the indicated malfunction, the cylinder head is dismantled from the engine and placed on a workbench. After that, it is completely disassembled, up to the extraction of the gas distribution mechanism from it.

The cleaned surface of the head is checked for distortion with the edge of a metal ruler. Putting the ruler on top along the length of the head, move it with your hands from one edge to the other, while carefully observing the lower edge of the ruler and the plane of the cylinder head. Any gaps found at this point indicate that the head is behaving, usually due to engine overheating.

To identify microcracks in the engine part under study, it will be necessary to make a kind of block head gasket from a piece of conveyor belt, with the only difference being that only holes for the combustion chamber are cut out in it.

Then the manufactured gasket is superimposed on the working surface of the cylinder head, organic glass is placed on top of it, cut into the shape of the head, and this entire “sandwich” is compressed with clamps. After that, the holes are tightly closed in the place intended for mounting the pump, and a hose connected to the air compressor is put on the fitting for the heater outlet.

The head prepared in this way is placed in a bath of clean water. Then the compressor is turned on and compressed air is injected into the water jacket of the part being checked, within 1.6 atmospheres. At this stage, the cylinder head is pressure tested. Any appearance of air bubbles will indicate the place where a crack has formed in the head.

Sources:

• Removal and installation of a head of the block of cylinders

Tip 2: The main causes and methods for eliminating engine cracks

Repair work related to the engine is one of the services provided by craftsmen at service stations. To do this, they are equipped with everything necessary. Often among the malfunctions there are breakdowns, the repair of which requires non-standard approaches. Among them are cracks in the engine housing. Therefore, it is recommended to entrust the solution of this problem only to experienced specialists.

There are several factors that contribute to the occurrence of cracks. First of all, these are mechanical damages resulting from an accident or impact (for example: unsuccessful dismantling, engine fall). In addition, temperature differences lead to the appearance of defects. This happens when either the coolant freezes. It happens that cracks form over time, from the wear of the metal.

Considering the problem of cracks, one must keep in mind that they can be both visually determined and invisible (microcracks). The first is not difficult to detect, and there are a number of ways to identify the second, this is done using special equipment.

The first way is with a sound tester. Its work is based on the principle of the difference in the speed of reflection of a sound wave from surfaces of different structure and thickness. This makes it possible to evaluate the dimensions of the cylinder walls and the integrity of the "jacket" walls.

The next method is using a magnetic tester. In this case, a metal powder is applied to the part to be tested, after which it is magnetized. From the pattern formed by the powder, it is possible to determine whether there are any damages on the surface being checked.

Another way to detect microcracks is with the help of ultraviolet radiation. To do this, the surface under study is covered with a special solution, after which it is magnetized. Then, in the dark, the ultraviolet lamp turns on. As a result, microcracks will be defined by contrast lines.

Another method is a photochemical process in which microcracks are detected by penetrating paint. It includes three stages of processing the tested part: solvent, special paint and developer. After that, the cracks become visible to the naked eye. The search for microcracks at some service stations is carried out by craftsmen on special stands, using high-pressure air injection.

Well, the easiest way is to grind the slate powder on the surface under study, and any crack will immediately appear.

Depending on the structure of the surface being checked and the accessibility to it, professional mechanics choose the best method of research to detect microcracks.