The injection mechanics is the main difference between a diesel engine and a gasoline engine. In a diesel internal combustion engine, fuel is supplied to the combustion chamber using a nozzle. The device injects fuel in a metered manner into a chamber with a high temperature and pressure, after which the diesel fuel ignites. The nozzle is subjected to the greatest load: the part is constantly in an aggressive environment and works at high intensity. Any negative factor can disable the part or significantly reduce its resource, after which the diesel engine nozzles will need to be repaired.
To understand the mechanics of the injector, we will describe the injection cycle schematically:
Let us describe the design of the part using the example of a primitive mechanical nozzle with 1 spring. In the lateral part there is a channel that provides a continuous supply of diesel fuel. Inside the nozzle chamber there is a movable barrier with a spring and a needle, which drops when the pressure rises. The needle rises, clearing the path of fuel to the sprayer.
Due to excessive loads, the injector may fail due to a violation of the operating mode of the motor. Manufacturers declare the resource of parts to be up to 200,000 km, but due to negative operating factors, wear of parts appears much earlier.
Usually, breakdowns are of the following nature: the spray angle and the amount of supplied fuel change, the integrity of the body is violated, and the needle travel deteriorates.
It is preferable to entrust the routine maintenance or overhaul of diesel engine injectors to qualified specialists - they will be able to restore and adjust the part on high-precision automated stands. However, a certain set of repair procedures can be carried out in artisanal conditions without the use of complex equipment.
It is recommended to carry out work in a dry and lighted, dust-free garage.
Diagnostics of diesel injectors and their maintenance involves removing the nozzles from the internal combustion engine. Before starting work, it is recommended to thoroughly wash the engine and engine compartment to avoid the ingress of debris and foreign particles. With particular fondness, you need to rinse the cylinder head. High pressure tubing should be marked with markings to avoid confusion during reassembly.
Before removing it is necessary to close the nozzle fittings (use plastic caps) to avoid contamination. It is not recommended to use ordinary open-end wrenches to dismantle the nozzles - an inexperienced repairman can strip the threads from the nozzles. If the required qualifications are not available, use spanners and a long-handled head tool.
After removing the nozzles from the holes, dry them and remove external dirt with a rag. O-rings are placed in the holes of the nozzles. When repairing injection parts, they are replaced with new ones without fail. Do not allow dirt from the rings to get into the injection system during removal.
There are several methods to check if the sprayer is working properly. The easiest way is to check the injector while the engine is running:
You can use a multimeter for diagnostics. In advance, it is necessary to throw off the battery terminals and disconnect the wiring of the injectors, and then "check" every detail with the device. On high resistance injectors, the device values will be in the range of 11 - 17 ohms; at low impedance, the multimeter will show up to 5 ohms.
The defective injector must be inspected. First, we look for leaks in the body of the part. If there are none, proceed to disassembling the part. We fasten the part in a vise and knock out the sprayer with a gentle tap. Next, you need a thorough cleaning: we soak the parts of the nozzle in diesel fuel or solvent to remove carbon deposits. Remove fumes and deposits with a fine steel grater. After completing the cleaning, you need to check the nozzle at the maximum meter. If the optimal injection parameters have been achieved, the device is ready to be installed in the engine.
In other cases, it is necessary to completely replace the atomizer on the defective nozzle. When installing a new part, carefully remove all factory grease, otherwise the device will not work.
Before disassembling the device, mark all parts with a marker to avoid confusion. Be especially careful when marking high pressure hoses. The nozzle is screwed in by hand as far as possible. Further tightening is done with a dynamometer wrench. For tightening values, refer to the motor manual. After installing the injector, evacuate air from the fuel system. On modern cars, for this it is enough to turn the starter several times; or use a manual priming pump (if equipped).
Please note that on some engines, after installing a new injector, it is necessary to "tie" it to the engine: make changes to the settings of the control unit.
Self-repair of injectors is a rather forced measure. Such a service in artisanal conditions can bring success only in the case of the highest qualifications of the master. The main problem of garage repairs is the lack of high-precision bench equipment for diagnostics. The repairman cannot objectively assess the effectiveness of the service measures.
If there is an opportunity to contact a service station, do not neglect it: computer equipment and cleaning stands will extend the life of the injectors and save them from potential expensive repairs. The same ultrasonic cleaning can save a motorist from engine problems for several seasons. It is not possible to repair modern Common Rail injection systems in a garage: you need a mandatory fine-tuning of the part by computer.
Use a cleaning fuel additive to avoid costly repairs and replacement parts. They prevent the formation of carbon deposits and the settling of deposits. The use of additives should be systematic, not one-off. Remember, additives are about preventing breakdowns, not fixing them.
Today, the Common Rail system is used in almost all modern cars, regardless of whether they are diesel engines or gasoline ones.There is an explanation for this phenomenon: the system is very efficient and reliable. But not every car enthusiast has a clear idea of how it works when it is necessary to restore or replace parts of this type. And many have a very superficial idea of the repair of injectors in this system. Let's understand these points in more detail.
The Common Rail system is today the latest stage in the development of diesel and gasoline engines with direct fuel injection. A feature of the system is that the injection process and the pressure build-up process in the fuel rail occur separately from each other.
That is, at first, high-pressure fuel is accumulated in the rail, and then in portions it is supplied to the nozzles for subsequent atomization in the combustion chambers. The fuel is pumped into the rail by a high-pressure fuel pump (injection pump), and the Common Rail system is controlled by an electronic control unit (ECU).
The main difference between the Common Rail system and gasoline fuel delivery systems is its incredible flexibility. A car enthusiast can very finely adjust both the injection parameters and the pressure level in the fuel rail, depending on the engine operating mode. All that is needed for this is to change the settings of the car's ECU. Changing the settings allows you to meet the ever-increasing requirements for exhaust emissions, engine noise levels and engine efficiency. Gasoline systems cannot provide such flexibility in principle. To change at least one of the above parameters and adjust it to the desired value, the owner of a gasoline engine will have to adjust it for a very long time.
Common Rail uses different types of this type of parts. They differ in both design and performance. Let's list the most popular models.
The vast majority of engines with Common Rail systems use piezoelectric injectors, since they are considered advanced and have many advantages.
As the name implies, the actuator is based on a piezoelectric element. Using such an element has a number of advantages:
Electromagnetic injectors are used primarily in gasoline engines. The needle in it is set in motion with the help of a spring and an electromagnet, and in one working cycle of the engine, the part can produce only one fuel injection. The design of this device can be found in the figure below.
Almost all malfunctions occurring in both diesel and gasoline injectors are associated with clogging. And the question comes down only to how exactly the blockage arose in the sprayer.
The so-called knock is a malfunction resulting from coking of the sprayer holes. The fact is that this part is regularly exposed to high temperatures. If the driver constantly uses low-quality fuel, resinous deposits accumulate on the nozzles.
Gradually, the surface of these deposits becomes covered with solid carbon deposits, and interruptions begin in the fuel supply. It is at this moment that the mechanism begins to "knock". Here are the signs of his knocking:
To eliminate, the device must be rinsed. Here are the main ways to flush:
A nozzle leak usually occurs due to the destruction of the O-ring underneath. Any, even the smallest crack in this part leads to a leak, since the pressure in the fuel line is very high. In addition, due to the collapsed ring, the fuel system loses its tightness and air begins to leak into the engine combustion chamber.
Diesel injectors are repaired when flushing is ineffective. All repairs, in essence, boil down to replacing the coked sprayer. If the problem persists, the return filter of the part is also replaced. To work, we need the following tools:
VIDEO First, we will consider the most acceptable option for a motorist: flushing the injectors without removing them from the car. To carry out this procedure, you will need the following things:
Wynns flushing fluid;
an empty plastic bottle with a capacity of 1.5 liters;
rubber hose 1.5 m long;
2 nipples for car wheels;
automobile compressor;
injector filter, 1 piece;
steel hose clamps, 4 pieces.
Before starting the flushing, you will have to assemble a simple washing device that will work as a dropper for the patient.
If self-cleaning does not give results, then the car owner will have to use the stand. It is not possible to make such equipment in a garage.Therefore, the car owner will have to contact a specialized service center, which has such stands.
During bench washing, all parts are removed from the engine, installed on the bench, where they are washed in a special solvent. In addition, they are sonicated. This comprehensive approach ensures the removal of even the most stubborn and stubborn dirt.
In most centers, flushing is performed at the stands of BOSCH and BLUSTAR. The cost of bench washing of nozzles varies from 1000 to 1800 rubles.
So, it is quite possible to repair and flush the nozzle yourself, unless the case is difficult. Well, if the contamination turned out to be very persistent and even a high-quality flushing liquid did not take it, there is only one option: to remove the parts and take them to the service center, to the ultrasonic stand.
We carry out repair of Bosch diesel injectors trucks and cars of any complexity for low prices .
This is what a Bosch injector looks like:
Solenoid (ramp. Electromagnetic head), anchor, ball, multiplier, spray, housing.
For more information on repairing a Bosch injector, see the article “Algorithm for repairing a bosch common rail diesel injector”.
A specialized tool is used to disassemble the injector:
Disassembling a nozzle with a non-specialized tool often results in the inability to assemble the nozzle or failure of internal components.
Solenoid. During operation, the car breaks down extremely rarely, this can happen due to a voltage drop. The most common reason for the failure of the solenoid is an unqualified check of the injector, the supply of high voltage to the contacts of the electromagnet (for example, supplying 12 V directly).
Anchor. There is nothing to break in it, you can only lose.
Ball. When assembling, the injector must be replaced with a new one.
Cartoonist. The main component that most often fails and must be replaced or restored. We change to new original ones, as this is the most reliable and high-quality repair option.
Spray. On Common rail injectors, the sprayer rarely fails. On average, it serves 150-200 thousand km, with a higher mileage it must be replaced, with a smaller one - cleaning in an ultrasonic bath.
Frame. Most often it fails when the injector is removed from the engine. It is diagnosed visually for the absence of cracks and deformations. You can replace it with a used one, if available, or order a new one.
The main problem after repairing injectors is incorrect installation on the car. When installing the injector, it is imperative to pump fuel through the injection pump to the injectors so that there are no air bubbles.
Undoubtedly, the best tool for this is an injector test stand, which can be the most complicated electronic one for thousands of dollars and very simple, even primitive in the spirit of the fifties (Fig. 7) or even home-made (Fig. 8).
Any of them, with a greater or lesser degree of convenience, can be used for work. There are many diesel garages and stands in the country, although they have the simplest ones. And we know how to negotiate. But what if your diesel is the only one in the area? Not very terrible efforts need to be made to make a homemade stand from a decommissioned tractor-KAMAZ or marine pump or to adapt the injection pump of your engine to check the injectors. Certainly not the most beautiful way, but without fish.
To do this, you need to make a tube - a tee, which at one end will be connected to one of the high-pressure fittings of your high-pressure fuel pump, on the other end we will attach the nozzle, and on the third - a 200-300 atmosphere pressure gauge (maybe more).First, we turn the engine with a starter until the nozzle starts firing, and then, remembering to leave the ignition on, manually. It is agonizing of course, but if there is no other way out, it is quite possible.
About injector opening pressure
During the compression stroke, the air charge from the cylinder flows into the combustion chamber at a very high speed. At the same time, due to its shape, a directed vortex appears in the combustion chamber, into which fuel is injected. Depending on the design of the combustion chamber and the degree of compression, the speed and shape of the vortex is different, therefore, there are different types of atomizers and different values of the fuel injection pressure. Designers set recommended as well as allowable injection pressures for each engine. As a rule, these values must be observed with an accuracy of 5-10 kg.cm2 within a set of nozzles. When the nozzle is overhauled, it makes sense to set the injection pressure by 10-15 kg.cm2 more than the required one, in the expectation that in the very first minutes of the nozzle operation there will be some shrinkage of the moving parts and, accordingly, a decrease in the set pressure.
It is especially necessary to note the specific property of the rotary-type distribution fuel pumps of the LUCAS company - very strict requirements for the accuracy of the injection pressure regulation within the set of injectors. For reference, in engines with such fuel pumps, it is often impossible to find a faulty injector using the shutdown method. The engine will immediately stall due to the cessation of fuel supply to the remaining injectors.
How to adjust the opening pressure of the nozzle at home
In the overwhelming majority of modern injectors, the opening pressure is regulated by adjusting the thickness of the spacer washer between the spring and the body. Decent workshops have sets of these washers to solve any adjustment problem. For amateurs, it should be borne in mind that washers exist of various diameters (for different nozzle bodies), and are available with or without a hole. Washers with a hole can always be used instead of washers without a hole, but replacement is not allowed. It is also unacceptable to use washers of "non-native" diameter.
As a rule, injectors are designed in such a way that an increase in the washer thickness by 0.1 mm leads to an increase in the injection pressure by 10 kg.cm2. It is very common to see when repairing injectors that, during previous interventions, the injection pressure was regulated using pieces of razor blades placed under a spring. This method of adjustment is completely unacceptable. First, with an uncontrolled backing, you create uncertainty in the spring support and thus non-uniform spring production and provoke lateral force. And secondly, there is a risk of chipping a piece of the blade and no one knows what he will do inside the nozzle. Therefore, the only qualitative solution to the problem is the manufacture of new shims of the calculated thickness. And only in those cases when the lathe, heat treatment and grinding are absolutely inaccessible, it is permissible to regulate the pressure with steel foil washers, placing them only between the body and the standard washer. If your spring rests on an unhardened lining, then after a short time, little will remain of it.
A typical problem with Japanese injectors
A distinctive feature of the injectors of Japanese engines is the “return” outlet through the end face of the injector into a special ramp. Careless disassembly often results in deformation of the nozzle sealing end, which is why it is not possible to achieve a hermetic “return” seal. "Experiments" begin with tightening the ramp nuts, with the setting of sealing washers under the nuts, etc. However, the only way to solve this problem is only to undercut the sealing end of the nozzle on a lathe.However, it should be borne in mind that only one surface of the nozzle is corrected by facing, and the shape of the groove at the end may be deformed so that the sealing washer can no longer cover it. This nozzle must be replaced.
Indefatigable attempts to tighten sweating or flowing return lines often lead to deformation of the return manifold flanges. Seals cannot be achieved with such flanges and must be refurbished. It is not difficult to do this by hand on a small sanded tile with sandpaper on top.
Sooner or later, everyone is faced with a significant increase in fuel consumption, a drop in engine power, there are times when the car refuses to move. One way or another, but the problem of the necessary replacement of nozzles may arise. The easiest way is to take the injectors to a diesel service, but then you have to pay a certain amount. There is no need to argue, this will be the most correct method. But the situations are different, for example, 200 km before the service, I think that a broken car will not pass them. But maybe the owner of the car thinks that he will cope with this problem no worse than auto mechanics, besides, he will save money? It was for such cases that the text was written. Also, the text will help you not to make mistakes, having familiarized yourself with it, you will help to abandon this venture in time.
So, we are trying to understand the structure of a diesel injector, as well as what is happening there and what affects what. In fig. 1, a shows a cross-section of the nozzle. All injectors (except for ultramodern ones) have a similar structure, the processes that take place in one type of injectors are similar to those that take place in others.
As a result, the operation of the engine is hard with shocks, the motor may refuse to accept the load. In addition, the ingress of combustion products into an unlocked system is not excluded, this can become a failure of the sprayer.
What then can prevent the normal locking of the system with outwardly intact parts? This can mainly be due to a lateral force that presses the needle against the nebulizer body. This force is fought by the intermediate pusher 10, which unloads the needle from the possible impact of a curved spring. The intermediate pusher is located in the spacer casing 3. But there are also cases when the pusher itself becomes the cause of the lateral force, the cause may be a depletion. That is, when replacing nozzles, you always need to be prepared for the fact that the new nozzle will "pour", if this happens, then you will need to repeatedly overhaul with the spring turning over or with its replacement, or you will have to replace the pusher. In rare cases, even the nozzle body will have to be replaced.
Everything else about the injector is pretty simple. Since the needle in the atomizer is not sealed, some of the fuel seeps into the gap between the atomizer body and the needle and enters the cavity “B”, where the spring 9 is located. , the resulting injector is “prohibited”. In order to remove the leaked fuel, the “return” channel is intended. only by the cleanliness of processing and the accuracy of the mating surfaces.
So, here we come to the very process of replacing the nozzles. Throughout the presentation, I adhered to the idea that you have a stand or apparatus that can replace it, on which, after the work done, you can test the injectors. With any work related to fuel equipment, it is imperative to observe the main rule - this is cleanliness.Please note that cleanliness should be not only during the direct disassembly of the injector, but at all stages, starting with the dismantling of the injectors from the engine.
Then there are only two options for the development of events: in the event that you have not yet replaced the sprayer, then you have deprived yourself of the opportunity to see what was wrong with your old sprayers. Second - you have doomed yourself to cleaning brand new sprayers (this procedure is not always successful). Hence the conclusion - the cavity of the nozzle must always be protected from dust, there is nothing to say about debris. By the way, tobacco crumbs, which are in your pocket in large quantities, have a destructive effect on the nozzle. By the way, it is best to remove the high-pressure pipes in a package together with ties (if the engine design allows it), so during the assembly process you will be less puzzled over how it all stood. For all the simplicity of this problem, thousands of people have suffered due to their negligence. If it is not possible to remove the tubes in a package, then we mark the fitting of the first cylinder on the pump, then mark the tubes themselves in the order in which they stood. As life shows, this can save a huge amount of time and nerves.
Removing the “return lines” will not be difficult. True, on cars of Japanese manufacturers, where you have to remove the “return” ramp, before you start to loosen the return nuts, you need to put on protective caps on the fittings. In order to remove the ramp itself, the caps will have to be removed, but then do not forget to put them on immediately.
But more often than not, the injectors are screwed into the body of the block head. In order to unscrew them, do not try to use an open-end wrench. Even if you managed to do this without damaging the nozzle without damaging it, I think it will not work to screw it back in without damage, since you will not be able to tighten the nozzle to the right moment. Almost all nozzles have a 24 or 27 hexagon, in order to unscrew them, elongated end heads are quite suitable. It is much more convenient to carry out this work with twelve-sided heads. If it is not possible to purchase elongated heads, you can get out of the situation, in this way: cut off its hexagonal part from the usual head and weld it to a piece of pipe from one end, and from the other end we weld a counterpart for the wrench. The problem has been resolved. It is not necessary to unscrew the nozzles immediately; first, it must be slightly shaken in the thread after being torn off. This is done in order not to instantly spoil the thread in the head or the head itself, since during previous intrusions, dirt could have entered the channel.
So, the injectors are removed. Now we immediately begin to remove the sealing washers from the nozzle channels, or rather their remains and debris in general. Removing the washers is often a painful dental procedure. As a rule, normal washers should simply be removed with a hook, but sometimes you have to come up with various individual “pull-outs” for this (for example, screw a tap into them and pull for it). In no case should you try to chop the washer in the channel with a chisel. You will definitely damage the end part of the channel, and correcting such notches will require removing the block head. Trying to solve the problem of a damaged end by installing clever washers, I boldly call it a gamble.
Having removed the injectors, first of all, you need to check their performance and make sure that the previous sentence was not erroneous. The main criteria for evaluating the work of sprayers:
when fuel is supplied, the injector must open only at a given pressure;
before the nozzle opens, leakage from the spray is unacceptable;
jets and drops are unacceptable during fuel injection;
the spray torch should be even, there should be no deviations (Fig. 2);
after stopping fuel injection, the injector must maintain pressure for some time.
They also talk about the characteristic sound of the injector operation, however, the sound should not be considered an objective parameter for evaluating the injector, but this parameter should not be ignored either.If it turns out that replacing the nozzles is really necessary, then we put on protective caps on the nozzles and start preparing the workplace. All preparation consists in thorough cleaning and washing of the table and the vice, you will need at least two baths with clean diesel fuel, the necessary keys (usually two) and, perhaps, you will need another knife - all unnecessary will interfere with the work. If you do not have a special device in your garage for fixing the injectors during disassembly. So, you will have to disassemble in a vice. I must say right away that the injectors of Japanese cars, whose “return” flows through the ramp, should never be clamped in a vice, since when clamping the edges of the sealing surface under the “return” they are crushed (Fig. 3).
Such injectors can be disassembled by placing them in a spanner wrench, which is clamped in a vice (Fig. 4).
But the nozzles of German manufacturers can be disassembled in a vice without harm to health. But you cannot use open-end wrenches to disassemble the injector. To begin with, this is rather inconvenient, but there is also a more important reason, for example, the union nuts of the injector housing of some engines (for example: Mercedes OM601,602,603) almost always crack when trying to assemble or disassemble them with an open-end wrench. And this part is quite expensive, and besides, it is not so easy to buy it. Therefore, for disassembling the injectors, we will use the same extended head as for removing it from the engine. We loosen the tightening of the union nut, then screw it with our hands. Often it can curl up with the spray that has stuck to it. The sprayer, after the nut has been removed, can be knocked out with a suitable rod, and the cavity of the nut can be cleaned with a brush to clean the battery terminals.
Of course, to complete this work, you need to move a couple of meters away from the clean area. The nut must be rinsed in the first bath - it will be for dirty deeds, after the nut, we put it to drain to the side on a sheet of paper. Now we begin to remove the intermediate body by rinsing it in a clean bath, drain the nozzle body, which is clamped in a vice, with fuel and put the intermediate body in place, do not touch anything else. We take a new sprayer without disassembling it, rinse it in clean fuel. After rinsing, it is necessary to pull out the intermediate casing or the sprayer (however, like all parts of the fuel equipment) from the tank after rinsing so that the flowing fuel carries away all dust particles from the mating surfaces (Fig. 5 and 6).
Thus, the procedure for replacing the sprayer will turn into a series of assemblies-disassembly-checks, you will have to repeat the same operations until you achieve the required result. Finally, we have achieved the desired result, the operation of the injectors suits us and they can be installed on the engine.
Before you start screwing in the injectors, you need to make sure, turning the crankshaft with the starter, that no water or other debris has entered the cylinders, and you can also look at the oil dipstick.
Re-assembly should not be a hassle, but this is in the event that you did not get excited and, when removing, marked all the pipes and fittings. Just a few tips. Flush the outside and spill fuel on the inside before installing the high pressure pipe. And yes, don't neglect to replace the clamps that collect the tubing into the bag. These clips are not for aesthetics. They prevent vibration from occurring. Tubes without clamps break very quickly (as if cutting them with a knife).
Well, everything seems to be, you can expel air from the equipment and try to start the engine. What is the best way to check the performance of the injectors is indisputable, it is best to use a stand for testing injectors, this stand can be the most complicated electronic one for several thousand dollars and very simple, one might even say primitive in the spirit of the fifties (Fig. 7) or homemade (Fig. 7). eight).
To do this, you need to make a tube - a tee, one end of which will be connected to one of the high-pressure fittings of the injection pump, on the other end we will attach the nozzle, and on the third we will attach a pressure gauge of 200-300 atmospheres, of course, more is possible, but this one will fit on the edge too. First, we turn the engine with the starter until the nozzle starts firing, and then, without leaving the ignition on, we turn it manually. Of course this is painful, but if there is no other way out, it will do.
During the compression stroke, an air charge flows from the cylinder into the combustion chamber at a tremendous speed. In the combustion chamber, due to its shape, at this moment a directed vortex arises, and fuel is injected into this vortex. There are different nozzles and different fuel injection pressures, depending on the compression ratio and the design of the combustion chamber, the shape and speed of the vortex are different. The designers set the recommended allowable injection pressure for each engine.
It should be noted the property of rotary-type fuel pumps of the LUCAS company - on these pumps there are strict requirements for the accuracy of the injection pressure regulation within the set of injectors. In engines with such fuel pumps, it is not possible to find a faulty injector using the shutdown method. Since the engine will immediately stall due to the fact that the fuel supply to the remaining injectors stops.
In most cases, the opening pressure of modern injectors can be adjusted by adjusting the thickness of the spacer washer between the body and the spring. Good workshops have a set of washers that can solve adjustment problems. But amateurs should know that there are washers of various diameters, they are designed for different nozzle bodies, and are available with or without a hole. Washers without a hole can be replaced with washers with a hole, but must not be replaced. It is also unacceptable to use washers of "non-native" diameter.
A distinctive feature of the injectors of Japanese engine manufacturers is the “return” outlet to a special ramp through the end face of the injector. If disassembled carelessly, deformation of the nozzle sealing end will occur; due to deformation of the hermetic return seal, it will not be possible to achieve. Some begin to "experiment" with tightening the ramp nuts and placing sealing washers under the nuts. The only way to solve this problem is to undercut the sealing face of the nozzle on a lathe. But keep in mind that only one face of the nozzle can be corrected by facing, so the shape of the groove on the face may be deformed so much that the sealing washer can no longer cover it. Only change such a nozzle.
Video (click to play).
Silly attempts to tighten the flowing or sweating return lines almost always lead to deformation of the return ramp flanges. Seals cannot be achieved with these flanges; they will have to be repaired. It's quite simple, you can do it by hand with sanded tiles by placing sandpaper on top of them.
