RESTORATION OF GUIDE BUSHINGS

A COMMON PART



The guide sleeve is the base, the basis of the service life of the "valve seat - valve disc" pair.
If the cylinder head is made of cast iron, then often the valve seats and valve guides are integral with the cylinder head. Such cylinder heads are used on some engines from OPEL, FORD, etc. But technological process The production of cast iron heads is complicated and requires expensive equipment, so most block heads are made from aluminum alloys. In their production, guide bushings and valve seats are made separately, and then pressed into their seats in the block head. Guide bushings are made of wear-resistant materials with fairly good thermal conductivity. These include special cast iron, cermets, bronze and brass of special grades. Bronze and brass are characterized by higher thermal conductivity, which is why they are used on most forced AUDI engines, BMW, VW and many other companies.
To fix the sleeve in the cylinder head in height, there is a support collar on its outer surface. Sometimes a split support ring is used. If the sleeve is smooth, then its installation in the head is carried out using a remote sleeve or a special mandrel
Inlet valve guides do not protrude too much into the intake port so as not to raise it aerodynamic drag. Guide bushings exhaust valves, on the contrary, they close the valve stem to the greatest possible length to protect it from hot exhaust gases and to better remove heat from the exhaust valve stem.
To ensure alignment of the valve seat and valve disc, the guide sleeve must be made with high precision. In addition, the outer surface of the sleeve, which is pressed into the head of the block, is treated with a high degree of surface finish for better heat dissipation and should not have marks or scratches. Due to this, heat transfer from the bushing to the head of the block is increased.
The main defect of guide bushings is usually increased wear inner surface caused by long-term (at least 150-200 thousand kilometers) operation of the engine. However, the use of low-quality oils and changes in the geometry of the pushers can lead to a reduction in the life of the bushings.

Long work engine with increased thermal gaps in valve mechanism causes uneven wear of the guide sleeve due to increased side loads on the stem and poor valve rotation.
Increased clearance in the "valve stem - sleeve" pair causes increased consumption oils, because the valve stem seal cannot retain oil with increased angular movements of the valve stem. This provokes the growth of carbon deposits on the valves and surfaces of the parts that limit the combustion chamber, increases the toxicity of the exhaust gases, and can also lead to premature failure of the exhaust gas catalytic converter.
Therefore, when repairing the engine, due attention must be paid to the head of the block. Sometimes it happens that in the loss of compression, to the honor of the engine, only its upper part - the "head" is to blame. It is very useful to check the clearance between the valve guide and the valve stem. If it goes beyond the tolerance recommended by the instruction, then the replacement valve stem seals and grinding will not bring the desired result.
How to determine the degree of wear of the bushing? There are two measurement methods: direct and indirect. At the first, you can not do without a caliper and a micrometer. The difference between the measured bushing inner minimum diameter and maximum diameter in the working area of ​​the valve stem and will form a diametrical clearance. In addition, it is necessary to take into account the change in the diameter of the sleeve in height and the conical or barrel-shaped wear of the valve stem. It is these values ​​that determine the so-called "chatter" of the valve in the sleeve. Measurements are recommended to be taken on a perfectly clean bushing bore and a completely clean valve stem.
For the second measurement method, you will need a dial indicator with a stand. Naturally, if the gap is more than recommended by the instructions, then all measurements will have to be repeated with a new valve. If in this case the gap is excessively large, it will not be possible to do without repairing the guide sleeve.
Many foreign firms, in particular, FORD, BMW, OPEL produce oversized valves with an increased stem diameter. In the presence of repair valves, the guide bushing unfolds first under the repair diameter of the stem, and then under the clearance required by the plant between the bushing and the valve stem.
To ensure minimal "removal" of the axis when unfolding the old block head bushing, it should be processed from the side of the less worn part, that is, from the area where the valve stem seal is installed.
The repressing of the guide bushings is carried out in cases where there are no repair valves, or there is an uneven "outrageous" wear of the bushings. For repressing, you must have mandrels and (preferably) a press. To facilitate landing, it is necessary to heat the cylinder head and cool the guide sleeve. This is necessary for less damage. seat in the head of the block and reduce the pressing force. In addition, it will not be superfluous to lubricate the hole in the head with liquid oil.
For example, when repairing block heads BMW engines For the 7th series VZOM, V35M, M 70, the block head must be heated to +50°C, and the valve guide should be cooled to -150°C.
Many companies, such as BMW, Mercedes, produce repair guide bushings with an increased outer diameter for pressing.
After the guides are pressed out, it is necessary to expand the hole in the head. At the same time, it must be remembered that the allowance for the formation of the final size for reaming should not exceed 0.02 ... 0.04 mm, and the surface after finishing should not have scratches, "blackness", roughness. It must be perfectly smooth.
If valve guides made of bronze or brass were used during the repair, then when they are subsequently unfolded, the gap between the valve stem and the sleeve cannot be deliberately underestimated, thinking that the denser the better.
Manufacturers recommend for guide bushings made of bronze and brass increased clearances (compared to those recommended for cast iron and cermet bushings). This is due to the large coefficient of linear expansion of these materials.
If this is neglected, then the "sticking" of the valve in the sleeve is inevitable, with all the ensuing consequences ( bent valves etc.)
An alternative option for restoring guide bushings is rolling out the inner surface of the bushing, followed by reaming to the required inner diameter. This is a less time-consuming method, but requires a special tool. When it is used, the seat in the block head under the guide does not deteriorate, and the inner surface of the sleeve in contact with the valve stem will have a greater hardness than the base material due to plastic deformation ("hardening"). This method is especially relevant for car owners whose engines have cast-iron block heads and valve guides are made directly in the block head. When worn, it is easier and cheaper to restore them by rolling than by boring and pressing new bushings.
Many firms - UTP, Sunnen and others - produce tools for rolling guide bushings. It allows you to restore bushings with wear of the working surface up to 0.5 mm, depending on the material of the guide. And the spiral groove remaining after processing increases the oil absorption of the surface, thereby improving the conditions for lubrication of the stem-bush friction pair. With effective gaps of 0.03 ... 0.05 mm, a gas labyrinth seal is obtained along the entire length of the sleeve. This reduces oil consumption for waste and reduces the toxicity of exhaust gases.
After forming the inner surface of the sleeve, you can proceed to the restoration of the valve seat with the NEWAY tool.






The inclined location of the knife-roller sets the pitch of the helical surface. The spiral grooves obtained as a result of rolling retain the oil well, improving the performance of the friction pair, and are a gas labyrinth seal.





RECOVERY HOW TO WORK
GUIDE BUSHINGS.


1. "Crack out" the head of the block with special crackers.
2. Use special pliers to remove the valve stem seals.
3. Remove the valves and make a thorough visual inspection. In doing so, pay attention to:
The condition of the valve stem for nicks, scratches, bending, steps. Special attention should be given to the place where the crackers fit. After unskilled cracking, nicks may remain. These nicks will lead to premature wear of the valve stem seal.
The condition of the valve disc. The valve must not have a sharp edge.
Use a micrometer to measure the diameter of the valve stem along the edges of the working area and in its middle. If these values ​​differ by more than 0.02 mm, the valve is rejected.
Record measurement data. If the decision is made to replace the valves, then it is necessary to clean the new valve from grease and measure the diameter of the valve stem. You can write down the diameter on the valve plate with a nitro-based marker.
Select reamers with a diameter that provides the required thermal clearance. Tip: It is always a good idea to measure the diameter of the reamer before working, rather than relying on a written value.


4. Thoroughly wash the head of the block with engine cleaner and use wire brushes to clean the dirty areas. Pay special attention to the cleanliness of the inlet and outlet channels.
5. Fix the block head in such a way that the axes of the guide bushings with which work is carried out are vertical. Saddles should be at the top.
6. Clean the guide bushings with a brush.
7. If a new valve is to be used, then it is necessary to go through the inner hole of the sleeve with a reamer equal to the diameter of the valve stem, then go through it with a reamer with a diameter that provides the necessary thermal clearance. To ensure minimal "removal" of the axis when unfolding the old block head bushing, it should be processed from the side of the less worn part, that is, from the area where the valve stem seal is installed.
8. Measure the inner diameter of the guide bushing along the height of the bushing and in different directions with a caliper. If these values ​​do not exceed 0.3 mm, then we can talk about the restoration of the sleeve; if these values ​​lie within 0.3 - 0.5 mm, recovery is possible, but there is no need to talk about a serious resource. If the differences in diameters exceed 0.5 mm, then the sleeve must be repressed. Repressing bushings is also required in the case of thin-walled 1.5 - 2.0 mm. metal-ceramic bushings. This type of bushing is found on a number of Japanese, Korean and German engines.
9. In case of sleeve restoration, a jig is selected, the guide of which corresponds to the internal diameter of the sleeve. Often there are intake and exhaust channels, in which the conductor cannot rest against the sleeve. In this case, it is allowed to refine the conductor with a cutting wheel. The main thing is that it should fit into the sleeve and not rest against the walls of the channel. Often in narrow channels, the conductor holder interferes with normal installation. In this case, you can remove it and use a screwdriver to keep the conductor from turning through the channel. These jobs require a certain skill and skill.
10. Particular attention should be paid to the installation of the drill stop. The top of the drill should protrude above the plane by about 2 - 2.5 mm. An increase in this value is not justified, and a decrease will lead to chipping of parts of the bushing when trying to insert the roller into the bushing.
11. When drilling the inlet hole for the roller, the following rule should be followed.
The center of the hole is located on a line passing through the axes of the bushings along the head of the block from the side of the seats.

12. After drilling the inlet hole, it is necessary to carefully clean the bushing with a brush.
13. Install the roller? 155 in the stem according to the instructions. Lubricate it with a drop of oil. Fix the through stem on the key for rotation and install the through stem in the sleeve so that the roller enters the entry hole.
14. If the stem is with a roller? 155 passes through the sleeve, you should take the roller? 165 and repeat the operation. If, in this case, the stem passes through the sleeve, the roller of the next size must be taken.
A WARNING! Never rearrange the roller through the size. In this case, breakage of the tool and bushing is possible.
In a smooth motion, begin to rotate the key clockwise. If you feel some force when turning, it means that the knurling process is successful.
15. As practice shows, bushings can be passed through the passage up to the roller? 175. Video clip? 185 can "shoot off" the seat under the oil cap. This is more likely for cast iron and cermet bushings. In this case, the guide bushing will have to be repressed, and heads without a pressed guide bushing will have to, in worst case, manufacture special tool to unfold the seat for the bushing (FORD).
16. After the roller passes, check the result by inserting the valve into the hole. If the valve is immersed by the amount of drilling of the inlet hole, this means that the sleeve is crushed and it is necessary to turn the hole with a reamer that provides a thermal gap. If the valve has stopped in the middle of the bushing, this means that the bushing is badly broken and needs further repair.
17. Particular attention should be paid to the cleanliness of the hole when working with cast iron and cermet bushings. Cutting products from reamer can obstruct the roller and cause tool breakage!
18. The work on restoring the sleeve is considered completed when, after passing through the reamer and thoroughly cleaning the hole, the valve play in the sleeve meets the requirements of the manufacturer and will be the same both in the longitudinal and transverse directions to the axis of the head. There is a saying: "The eye does not see, the hands hear." This refers to backlash. It should be remembered that with the same clearance, a longer sleeve will have less play than a short one.


If repressing the bushing is unavoidable, the tool must first be prepared. It includes:
Reliable massive support for quick fixing of the head of the block from movement in the vertical and horizontal planes, which will ensure the safety of the studs.
Sledgehammer 2 kg or press.
Equipment for pressing out and pressing in a bushing of a given size and a spacer.
Heating cabinet up to 150°С.
Canvas mittens.
Caliper with depth gauge.
Oil.
Special compound for cooling bushings, such as "liquid nitrogen" or "dry ice".
Thermos for cooling bushings.
Tweezers.
Micrometer 0 - 25 mm.
Reamers that ensure the processing of holes for pressing in with the required interference. The use of adjustable reamers is allowed.
It is assumed that the bushings for pressing in are of high quality, i.e. correspond the right size and made from the required materials.


Before repressing the bushings, you must:
1. Place the block head in a heating cabinet and heat evenly to a temperature of about 90...100°C. (for most engines)
2. Protecting your hands with canvas gloves, move the block head to workplace and secure it with saddles up.
3. If there are no thrust collars or rings on the bushing, use a vernier caliper to measure the protrusion of the bushing from the side of the oil scraper cap above the support plane for the springs. This value must be recorded and fixed on the caliper.
4. Using a mandrel and a sledgehammer or press, remove the bushing.
5. Allow time for the head to cool naturally.
6. Measure the outside diameter of the guide bush and the inside diameter of the bore. The difference between these values ​​should provide an interference fit in most cases of 0.05 - 0.07 mm.
7. If an oversized sleeve is used, it is necessary to turn mounting hole under this bushing to ensure the required tightness.
8. Repeat the operation to heat the block head. 3 - 5 minutes before pressing, put the sleeves in a thermos and cool them.
9. After heating, grease the holes for the bushings with oil.
10. Using tweezers, remove the bushing from the container, put it on the mandrel for pressing.
11. Drive in or press in the sleeve to the required depth, noting the pressing force. It should not be excessively weak or strong. If the preload was correct, these problems should not be.
12. Cool the block head naturally.
13. Expand the bushings with a reamer that provides the required thermal clearance between the bushing and the valve stem.

Among the possible causes of increased oil consumption can be noted, in order of difficulty of elimination:

1. oil leaks through leaks in gaskets, seals, as well as cracks in the engine crankcase, cylinder block, oil pressure sensor, etc.
2. oil seal wear
3. wear of the cylinder-piston group
4. oil burnout due to its poor quality

The first group of causes is determined by visual viewing. Eliminating such causes, with the exception of the HEAD gasket and cracks in the cylinder block, is quite simple. It is only necessary to replace defective parts (seals, gaskets). The exception is here - the head gasket and the cylinder block. To replace them, you must remove camshaft(with all the ensuing consequences), and then - the head itself; and then completely disassemble the engine. Of course, such an operation will not be difficult for an experienced mechanic, but for an ordinary motorist ...

The second reason is the wear of low-removable caps. We will talk about the signs of the need to replace them a little lower. This operation also involves, as a rule, the removal camshaft(one or more - depending on the model of the car). However, there are cars on which this is not necessary. However, these are quite rare cases.

Finally, the wear of the parts of the cylinder-piston group. To eliminate it, it is necessary, as they say, to overhaul the engine. As a rule, it is timed to coincide with other repair operations, namely: replacement of liners crankshaft, repair (grinding) of the crankshaft journals, replacement of valves, replacement / reaming of valve guides, not to mention the replacement of worn (by that time) valve rockers, valve springs.

Here we look at signs that indicate symptoms similar to wear and tear. valve stem seals. Here is a list (perhaps incomplete):

Alarm malfunction

Smoky exhaust when regassing

Increased fuel consumption

Drop in power and throttle response, dips in engine operation,

Oil gets dirty quickly

glow ignition

Note that it is not necessary that all signs appear at the same time.

Smoke from the oil filler neck*

Which can sometimes be seen, for example, if the oil filler neck is opened on a running engine. On a good (i.e. serviceable) engine, air will simply come out from there (as an option - with an admixture of oil mist, which is not a malfunction). If the engine consumes a lot of oil and strong smoke comes out of the neck, it means that the piston group. If the engine consumes oil, and it is clean from the neck, then the matter may be (but not necessarily) in the valve stem seals.

* So this symptom is more likely not indicative of wear on the valve stem seals.

The threaded part of the candles is coated with oil

This is also one of the symptoms of the need to replace valve stem seals. However, not always. Those. it happens that the caps already require replacement, but the threaded part of the candles is still dry. For there is still not too much oil getting into the combustion chamber, it has time to burn out.

Why is the threaded part of the candle covered with oil under the conditions when it enters the combustion chamber? It would seem that if there are gaps in the thread between the spark plugs and the block head, then they are minimal and do not exceed 0.2 mm?

Consider the process of the engine. The fact is that at the moment of inlet of a portion of the combustible mixture, oil enters the cylinder, while there is a vacuum in the cylinder (as well as in the threaded gaps of the candles). The mixture is then compressed. Naturally, it (including the oil and gasoline contained in it) begins to penetrate into all places where it is possible, including the threaded gaps of the candles. The mixture is then ignited and burned. It burns almost everywhere, except, just, for threaded gaps. For they are very small (in the region of 0.1 ... 0.3 mm), as a rule, combustion cannot spread into such small gaps. As a result, oil accumulates in the threaded gaps. Gasoline evaporates, because the candles are heated.

Candles are covered with black soot. Increased smoke from the exhaust pipe

Nagar can (but not necessarily) be oily. As a rule, when the valve stem seals are worn, it is terry. Although, too rich mixture can also give terry black soot. Blue-gray, sometimes black smoke from the muffler indicates wear of the cylinder-piston group, as well as an excessively rich mixture.

However, similar symptoms are also observed when the valve stem seals are worn out (blue exhaust during regassing), the ignition system malfunctions (the ignition timing is incorrect, “broken” high voltage wires, distributor cover, slider, etc., as well as, possibly, a malfunction ... of an alarm), violation of the adjustments of the fuel supply system (for example, carburetor, injectors, etc.).

Those. black smoke from the muffler and black-coated candles are far from always evidence of an overly rich mixture. Both of these signs also appear both when the valve stem seals are worn out, and when the ignition system is disturbed. Why?

Because if the ignition system malfunctions, the spark on the candles will be defective, although in appearance it may be quite acceptable. Accordingly, the combustion of the oil-fuel-air mixture will also be defective. In particular, the oil and gasoline contained in the mixture will burn WORSE (than with a good spark), i.e. black soot will form, giving the appearance of an overly enriched mixture. For example, this is exactly what was observed in the case when it was “cunningly” broken.

Alarm malfunction

It can also be the cause of carbon deposits on spark plugs if circuits related to ignition pass through it. A common case is when some connectors in the alarm have bad contacts (when they are old and / or made of Chinese metal). In this case, the ignition will be either excellent, or “not very”, then (for a fraction of a second) it will be completely absent. And so - all the time.

There was a case when the car periodically stalled on the move after 10 ... 20 minutes of driving. And after - flatly refused to start. However, after a 10 ... 15 minute parking incident, it started up, as if nothing had happened and drove as long as necessary.

Note: exactly the same behavior of the machine in another case was the result of a malfunction of the valve stem seals.

In addition, the car often (but not always) stalled when trying to move uphill. The recommendations of the servicemen to repair the power system, of course, did not lead to anything at all. They only cost Money and time for reflection. However, the problem was completely removed after the restoration of electrical contacts in two alarm connectors (by removing them and lightly crimping the connectors).

Why did the car start after 10 ... 15 minutes of parking? Because during this time the alarm unit cooled down a little, the contact parts of its connectors slightly changed in size (under the action of thermal constriction), slightly shifted relative to each other (i.e. the “father” connector slightly shifted relative to the “mother” connector ”), there was a sort of scratching, slippage of their contacting surfaces relative to each other, and contact was restored again for some time.

Why does the engine sometimes stall when driving uphill? Because in the signaling unit, which is under dashboard, when changing the orientation of the machine relative to the vertical, the signaling unit moved slightly to a different position, as a result - sometimes violated electrical contacts. And when the car moved to a horizontal surface, contacts were restored.

Smoky exhaust when regassing

Symptoms of the formation of smoky exhaust during regassing are similar - both in the case of a malfunction of the valve stem seals, and in the event of a malfunction of the cylinder-piston group. The difference is that if the caps are faulty, then repeated regassing (4 ... 7 times) usually leads to the (temporary) disappearance of smoky exhaust. Those. There is usually no permanent smoke. Whereas in case of malfunction of cylinders and pistons smoky exhaust after several peregazovki DOES NOT DISAPPEAR.

The reason is that in the first case, the oil accumulated near the junction of the edge of the valve stem seal and the valve stem, as a result hard pressing on the gas pedal, is TEMPORARILY sucked through the gap between the valve stem and the guide sleeve, into the cylinder, which leads to several smoky exhausts during regassing. When all the nearby oil has been sucked out, there will be no smoky exhaust (until the oil accumulates again). Whereas in the latter case, oil enters the cylinder, regardless of whether the gas pedal was sharply pressed or not; no matter how many times and with what frequency it was pressed.

When working on Idling when the cylinders and / or pistons are worn, the smoke will be thick and bluish (like old Soviet motorcycles, chainsaws of the “Friendship” type), while when the valve stem seals are worn out, it will (at first) seem to be “bluish”. If you look at the exhaust pipe from above with the engine running, it is not always visible. And here is a look ALONG exhaust pipe, when viewed from behind the car, sometimes (but not always) makes it possible to see such a bluish haze.

Also, if, with the engine WARM, smoke from muffler goes white, then this is also a sign of wear of the valve stem seals, but not of the cylinder-piston group. By the way, another reason for the appearance white smoke on a warm engine - the ingress of coolant into the engine cylinders due to a malfunction of the head gasket.

Note that the appearance of white smoke disappearing after warming up on a COLD engine, on the contrary, is a completely normal symptom. After all, as a result of combustion fuel-air mixture formed, in particular, water. The vapors of which become visible until the engine and muffler warm up. For the same reason, water drops can even fly out of the muffler. It often happens that water drips a little from the end of the muffler pipe.

When the muffler warms up, the water vapor on its walls will no longer condense - and the white vapor will disappear. The water will stop dripping.

Too rich a combustible mixture will also give an exhaust of increased smoke, including during regassing. Which, it seems, SHOULD NOT disappear after repeated regassing.

However, in fact, not everything is so simple. There was a case when, due to too rich fuel mixture the car engine with great difficulty started "hot" (whereas "cold" started with half a turn). After repeated re-gassing, the exhaust of increased smoke (blackish) DISAPPEARED. However, the problem was - it was in an overly enriched fuel-air mixture.

Increased fuel consumption

The fact is that the oil that enters the cylinders during engine operation makes it difficult for the combustion of the fuel-air mixture. Accordingly, in order to remove the required power from the engine, a larger amount of mixture will be needed than in the absence of oil in the mixture.

By the way, not only valve stem seals, but almost all other engine malfunctions also lead to increased fuel consumption, whether it be wear of the cylinder-piston group, a malfunction of the ignition or alarm system, or a non-optimal composition of the combustible mixture.

Loss of power and throttle response, failures in engine operation

This manifests itself in reduced dynamics when accelerating, overtaking. And also there may be "failures" when you press the gas pedal. Those. you press the gas, and the car SOMETIMES, instead of jerking forward, it seems to slow down, the engine stalls. If you release the gas pedal or press it SLOWLY, the engine runs normally. In such cases, it is usually recommended to adjust or repair the fuel supply system. More advanced ones also recommend paying attention to the ignition system.

This is often true, but not always. Sometimes - with a sharp increase in vacuum during the intake stroke of the fuel-air mixture (which is the result of a sharp pressure on the gas pedal), this vacuum is transmitted, through the valve guides, to the valve stem seals. If they are worn out, then a portion of oil is sucked in, which enters the cylinder, filling the spark plug, i.e. (at first - temporarily, and then - permanently) turning it off from work. This explains the "failure" in the engine. If the vehicle is equipped catalytic converter, he "for some reason" will soon fail.

Oil gets dirty quickly

Yes, this is also one of the symptoms of valve stem seal wear, which is far from known to everyone. Why oil becomes dirty, acquiring a dark, then black color? There are usually two main reasons for this:

1. wear of engine parts and the ingress of wear products into the oil
2. soot formation caused by the combustion of oil contained in the fuel-air mixture and its subsequent flushing

Well, quite banal reasons, for example, disruption of work (or absence) air filter, as a result of which dust from the air enters the cylinders, which causes oil pollution or simply low-quality oil that quickly collapses during engine operation, we will not consider here.

The first is generally known. But, at the same time, there should be metal particles on the magnetic oil drain plug. And if there are few or none at all?

Then, obviously, the black particles that cause the oil to darken are nothing more than coke washed off the cylinder walls. Indeed, in most modern engine oils contain quite effective detergent additives, which help wash off soot. If not for them, then as a result piston rings would simply coke. Fast. Well, their presence in the oil saves, thereby, the engine. True, the whole blow is taken by the oil, which quickly becomes contaminated.

Since soot is formed GRADUALLY, its particles are very small in size, they, being washed off from the walls of the cylinder, freely pass through oil filter and for this reason remain in the oil, causing the need for its accelerated replacement.

However, too rich a mixture can also take place here. Which also gives black soot on spark plugs, as well as on the surface of the cylinder. Accordingly, after this soot is washed off with oil, it will enter the engine crankcase.

glow ignition

It is expressed, in particular, in the fact that the engine continues to run for several seconds, or even more, even after the key has been removed from the ignition. Yes, and this can also be a symptom of oil getting into the combustion chamber, including as a result of a malfunction of the valve stem seals. Why?

Because modern gasoline cars, perhaps, without exception (both carburetor and injection) are equipped with a fuel cut-off system when the ignition is turned off. For example, if we talk about carbureted car, then in carburetors, as a rule, there is solenoid valve idling, which blocks the flow of the working mixture when the ignition is turned off.

By the way, for reference, modern petrol car does not have to be injection. For example, many military vehicles are, as before, carbureted. The reason is probably clear to you: military vehicles are required, among other things, increased reliability and high maintainability even in the "open field". It is clear that a knowledgeable person will be able to clean and adjust the carburetor quickly and in almost any conditions, while for adjustment injection engines can't do without a computer. Well, cleaning nozzles in the "field" is definitely impossible without special equipment. And, in fact, the military will not carry a diagnostic computer and other devices with them just to use the injector, when it is quite possible to get by with a carburetor that has proven its reliability and quick maintainability. Well, which slightly increases fuel consumption, slightly increases the toxicity of exhaust gases. And, nothing more.

Then, the more electronic parts in the car, the higher the probability of their failure, for example, when exposed to an electromagnetic pulse.

So, if even when the gasoline supply is turned off at idle, the engine continues to work, therefore, there is something in its cylinders that can burn out. AT this case It is nothing but oil. Located there in SUCH concentration at which the engine is still able (but not always) to work. It is clear that when the caps are even more worn out, even more oil will enter the combustion chamber, then the glow ignition may disappear. But, at the same time, the car will be difficult to start, there will be increased oil consumption, etc.

The car is difficult to start "hot"

If it is difficult to start “cold”, then the reason is often not at all in the valve stem seals. There, most likely, more obvious reasons, such as wear of the cylinder-piston group, fuel supply failure, ignition malfunction, including, as already mentioned, alarms. And also - a malfunction of the battery, starter.

But if “on a cold” engine it starts with half a turn, but on a hot one, paradoxically, you have to spin it with a starter for 5 ... 10 seconds or even more (or even the car’s engine stalls as soon as it warms up well), then the reason for this may well be be worn valve stem seals.

The fact is that in a cold engine, the oil is also, of course, cold. And having a high viscosity, and therefore - reluctantly leaking into the gap between the valve stem and the working edge of the valve stem seal. When the oil warms up, its viscosity decreases (sometimes by several orders of magnitude), and it is much easier for it to pass into this gap.

However, a violation of the composition of the combustible mixture, ignition malfunctions, alarms are also not excluded, of course.

Exhaust gas has a very disgusting, suffocating smell.

It is clear that the smell of exhaust gas cannot be called natural, pleasant and safe.

However, sniffing, say, to cars driving in Arab Emirates(UAE), I concluded that there with exhaust gases things are MUCH (!) better than in Russia. It seems that a continuous stream of cars is driving, and the exhaust smell is insignificant ... Sometimes, even leaning close to the exhaust pipe, somehow you don’t catch that nasty smell that comes from Russian cars. One of the reasons for this is, of course, quality gasoline. Which, by the way, was also much cheaper than in Russia, at least until the ruble was sharply lowered against the dollar and many other currencies.

Yes, after all, after all, exhaust gas, what to expect from it. However, when the combustible mixture is of poor quality, incorrect (in particular, as a result of a large amount of oil in it), then, naturally, the smell of the exhaust becomes much, much more disgusting. In such cases - it is worth standing a little near the exhaust pipe when the engine is idling - and you want to get away from this smell somewhere. The neutralizer, we repeat, at the same time fails very quickly.

Therefore, if the exhaust of a car has become somehow especially unpleasant, suffocating, not the same as it was before, you should pay close attention to engine parts through which excess oil can enter the combustion chamber. In particular, these are valve stem seals.

However, a very rich combustible mixture can also be the cause of such a smell.

Worn valve guides, valve stems

Of course, the wear of their working surfaces in itself does not indicate the wear of the valve stem seals. He simply speeds it up, and significantly. It also makes it useless to replace the caps with new ones.

The fact is that if the holes in the guide bushings and / or valve stems are badly worn out, even a new high-quality valve stem seal will not be able to fully retain oil during engine operation. Which will enter the combustion chamber, as with worn caps.

So if, after replacing the valve stem seals, those symptoms of wear remain, then you should think about repairing (replacing) the valves and their guide bushings. And then about overhaul(replacement) of the engine, because, as a rule, by such a time, its other parts are also partly exhausted. It makes no sense to change only the bushings and valves, if after another 20 ... 30 thousand the chain, sprockets (pulleys), rockers, pistons, rings, as well as cylinder boring, grinding of the crankshaft journals are to be replaced.

How to measure play in valve guides? If roughly and approximately, then the backlash can be considered large if, when the valve stem is swaying from side to side, it feels much higher than it was on a new (refurbished) engine. If it is much higher than the typical felt backlash for a particular engine model. Well, for a more accurate measurement, of course, you need to remove the block head, get the valves, etc.

With respect to you.

According to the site "Irkutsk Express"

It's good when the car is new - the engine runs quietly, you can't hear it even when accelerating with full throttle. But time goes by - and one day you notice that there is no trace of the former "silence", and, opening the hood, you see some kind of rumbling beast, which, along with the usual singing, makes sounds that are clearly offensive to the ear.

The noise of the engine is most often associated with the gas distribution mechanism - large gaps and knocking are always adjacent to each other. The first thing that comes to mind is to adjust the valve clearances. Often this helps, but sometimes after adjustment it seems that the knock has become even stronger: one or more valves continue to knock. And it is completely incomprehensible why: after all, the gaps are normal, and the camshaft looks good. The reason does not seem to lie on the surface, it is somewhere inside, but where? It would be necessary to understand, but there is no time. And the knock gets louder.

The fact that the valve is a responsible part does not need to be explained to anyone. And the fact that valve malfunctions are not only serious, but also dangerous, many people know firsthand. These errors occur for various reasons. And there are among them completely unobvious, so that during repairs it is not possible to confine oneself to replacing a faulty part.

By the way, in any case, before you repair or change anything, it is useful to find the cause of a particular malfunction. Otherwise, the same fate in the near future may befall a completely new, just installed part. And to prevent this from happening, it is desirable to know in what conditions it works.

How does the valve work?

The main task of the valves is to control the flow of the air-fuel mixture and combustion products entering the cylinder or flowing out of it. Therefore, when the valve is opened, it must freely pass the mixture or gases, that is, it must have a minimum hydraulic resistance. In the same time closed valve must ensure tightness and completely separate the cylinder cavity from the inlet or exhaust system engine.

Valves operate in conditions of strong heating from hot gases flowing around their plates. And if inlet valve when opening, it is periodically cooled by the incoming cylinder air-fuel mixture, then graduation works in much more stringent conditions. Opening on the exhaust stroke, it heats up even more with hot exhaust gases, and the temperature of its plate reaches 850-900 degrees. WITH.

In order for valves to withstand such thermal loads, they have to be made from special heat-resistant steels and alloys with great content chromium, nickel, molybdenum and even tungsten. These materials are very expensive, which is why exhaust valves are often made of dissimilar materials: the plate is made of a heat-resistant alloy, and the stem is made of alloy steel. By the way, the intake and exhaust valves of the most different motors very easy to distinguish: the exhaust valve discs are not magnetic.

To reduce chamfer wear at high operating temperatures, a special hard material, stellite, is often deposited on it. Sodium cooling of the valve is less commonly used: sodium moving in the internal cavity of the valve when it is opened and closed transfers heat from the hot plate to the colder rod.

Practice shows that even the most heat-resistant valve will still burn out if some other conditions are not met, the main of which is a tight fit of the plate in the saddle. The point is that only good contact valve with a seat allows you to reliably remove heat from a heated plate. After all, the seat is quite cold, it is pressed into the body of the head of the block with a cooled liquid.

Up to 75% of all heat entering the plate is removed through the saddle - a very, very significant part. Naturally, if contact with the saddle is broken, the plate immediately begins to overheat. This means that the valve does not have long to live before burnout.

It looks like a chain reaction. A small leak in the mating of the plate and seat leads to a breakthrough of gases. There is no heat removal from the plate in this place, and the plate overheats. The looseness increases, and with it the temperature of the plate also increases. Eventually the material begins to break down, more hot gases rush in, and the poppet defect spreads rapidly until the cylinder is completely out of service due to lack of compression.

As you can see, a good pairing of the plate with the seat "kills" "two birds with one stone" at once: it reduces the temperature of the valve to an acceptable level and ensures tightness. And it's hard to say which is more important. At least for the performance of the valve itself, the first is important, and for the engine as a whole, the second (meaning good starting properties, power characteristics, economy).

In addition to these conditions, the operation of the valve (opening and closing) must be sufficiently "soft" and not cause excessive noise. Noise or, more precisely, valve knocking is a sure sign of a malfunction, and the shock loads that occur during knocking often themselves cause even more serious malfunctions and even valve failures.

Where does the knock come from?

There are several reasons. The simplest one has already been mentioned - a large gap in the drive. Because of this, the camshaft cam runs onto the pusher (lever or rocker) not smoothly, but with a blow, which is the stronger, the larger the gap.

What suffers in this case in the first place? What takes up the shock load: the working surfaces of the camshaft cam and pusher, as well as the bearing surface of the pusher and the end of the valve stem. They often form damage in the form of punctate shells, which later expand and deepen.

But the matter is not limited to this. The valve not only opens with a blow, but also closes abruptly, with a knock. This means that the shock load during closing falls on the sealing chamfer of the valve and the seat. In addition, at the moment of impact when landing on the seat, a large tensile load from the spring acts on the valve stem. Prolonged work in such conditions is very dangerous: the plate can simply come off the rod or the rod will collapse in another way. weak point- a groove for crackers.

But let's assume that the gaps in the valve drive are normal, but the knock is still heard. Most often, the reason for such a knock lies in big gap between valve stem and guide bushing. This situation is most typical for old, fairly resembling, motors. Sometimes valve knocking is associated with a misalignment of the seat and guide bushing hole, which is the result of overheating of the block head or improperly performed repairs. In this case, the valve sits on the seat first with one edge of the plate, and only then, rolling in the sleeve within the gap, completely. Because of this, by the way, the wear of the guide bushing progresses rapidly.

Rapid wear of the guide bushing and valve knocking also occur for other, more complex reasons. For example, when the seat of a cylindrical valve lifter is misaligned or misaligned with respect to the sleeve. This defect is sometimes found in domestic motors. Knocking is also possible due to increased clearances in the drive parts - in the axes of the rocker arms, in the sockets of the cylindrical pushers, and also in the camshaft bearings.

All these knocks are quite similar to the ear, and therefore it is often not possible to isolate a specific cause without disassembly and careful revision of the condition of the parts. But in any case, you need to keep in mind that since there is a knock, then the loads at the points of contact of the parts are of an impact nature. As a rule, such a knock progresses rapidly, which threatens not only with wear of the valves and associated parts, but also with their breakdown.

Why did the valve break?

Knocking by itself may not cause a breakdown. But in any case, it is important to understand why the valve began to knock? And the reasons that provoked the appearance of a knock, it turns out, are many ...

The most common is illiterate operation, unskilled and untimely engine maintenance. Obviously, adjusting the clearances in the valve drive from case to case - the right way accelerate wear, cause knocks, and then breakdowns.

It is very dangerous to set too small gaps when adjusting: when the engine is running, the valves will heat up, their length will increase, and when the gap is fully selected, the valves will “hang”. And then a loose fit on the saddle will lead to overheating of the plates and burnout.

A fairly common cause of exhaust valve burnout is ignition too late. Especially if the engine has been running at high speeds and loads for a long time. But also early ignition- also not a gift for valves, because the temperature of the gases in the cylinder in this case is maximum. Means, incorrect installation Ignition advance causes not only a loss of power and an increase in fuel consumption, but also valve malfunctions.

Usage poor quality oil- too possible reason wear of bushings and valve stems. In addition, such oil tends to coke at the bottom of the valve stems. Because of this, the valve will go tighter and tighter in the sleeve, and then it may completely jam in it. In the end, he will get the same piston on the plate with all the ensuing consequences.

Soot deposited on valve plates (especially inlet ones), for example, due to wear of valve stem seals, is also not a harmless thing. Reaching a solid thickness, soot begins to chip off. And the particles are pretty large sizes can easily get between the chamfer and the valve seat. And after that bad contact with a saddle and overheating of the plate is inevitable.

It is interesting to note that significant carbon deposits on the valves that cause such troubles are far from always associated with wear on the valve stem seals. Judge for yourself: high blood pressure in the crankcase, due to a malfunction of the ventilation system or wear of the cylinder-piston group, it can easily squeeze out oil to the valve plates even through the newest caps.

Some "hotheads" prefer to disconnect the crankcase ventilation hose from the air filter and lead it somewhere under the bottom of the car - so supposedly the engine "breathes easier". And they are unaware that in some modes a vacuum is created in the crankcase, and the dust sucked into the engine through the hose not only quickly pollutes the oil and oil filter, but also gets to the valve guides and valve stems. Comments, as they say, are unnecessary.

But perhaps the most serious consequences for the valves are fraught with non-compliance with the timing of replacing the camshaft drive belt. On many modern motors valves in the event of a broken belt are deformed. Let's add that attempts to put new belt and so to get, for example, to the garage, rarely end happily. Deformed valves experience heavy bending loads every time they are seated and usually break after 10-15 minutes of operation. And such a valve failure is, at a minimum, the replacement of a piston, block head, connecting rod.

Whole line problems are introduced into the operation of the valves by poor-quality repairs. For example, most "experienced" mechanics don't bother using special valve spring compressors. Their "crown" tools - a steel pipe and a hammer, hit harder - and order. Only now the valve can get damaged along the cracker groove. And then, much later, break in this place.

Very dangerous hit abrasive paste into the guide sleeve while lapping the valve against the seat. Washing such a sleeve is a whole story. But if this is not done, the story will turn out with a continuation of a maximum of 5-10 thousand kilometers. After that, the wear of the sleeve and the rod is likely to exceed all reasonable limits.
Some mechanics strive to keep the valve clearance in the sleeve as small as possible. This misconception often leads to valve jamming with a very backfire.

Another mistake is lapping valves without straightening the seats. As practice shows, after long-term operation and especially after replacement of guide bushings misalignment with seats is common. In such cases, lapping alone is likely to result in valve knocking and rapid wear details.
When the head of the block is fully assembled with the valves, it is very easy to ruin the whole work by tapping the valves with a hammer. The result can be the same as with "impact" disassembly, especially in modern multi-valve engines with small diameter valves.
From all these factors, a fairly clear picture emerges, when the valve is faulty, it is likely that someone "helped" him in this. And the task of a mechanic is not only not to become another "assistant", but to eliminate all the consequences of the previous "assistance" that valves and other parts usually bear after a long work. This is the only way to be sure that the valve will not fail.