Audi 100/A6

1990-1997 of release

Repair and car operation

Audi 100/A6
+ 1. Maintenance instruction
+ 2. Maintenance
+ 3. Engines
+ 3.2. Diesel engines
+ 3.3. Removal and partition of engines
+ 4. Cooling system
+ 5. Heating and ventilation
+ 6. Fuel system
+ 7. Exhaust system
+ 8. Systems of start, ignition
+ 9. Transmission
+ 10. Brake system
+ 11. Suspension brackets, steering
+ 12. Body
+ 13. Electric equipment
- 14. Good advice
   14.1.1. Changed numbers
   14.1.2. Purchase of the old car or mysterious set of figures and letters
   14.2. Durability of the car
   14.3. About parallelism of bridges of the car and the trailer
   14.4. Preparation of the car for winter
   14.5. It is not got – good advice
   14.6. From change of places "composed" changes nothing?
   14.7. Visit to car-care center
   - 14.8. Engine
      14.8.2. Analysis of a dymnost of an exhaust
      14.8.3. "Eats" much, but silently goes
      14.8.4. A gear belt for a drive of the mechanism of a gazoraspredeleniye
      14.8.5. That it is necessary to know, changing oil
      14.8.6. Pistons
      14.8.7. Valves
      + 14.8.8. Bearings
      + 14.8.9. To owners of the car with the diesel engine
      14.8.10. To owners of the car with the injector engine
   + 14.9. Conditioner
   14.10. Turbokompressor
   + 14.11. Rub in one – or how to save the catalyst
   + 14.12. Accumulator
   14.13. Generator
   14.14. Probuksovochka
   14.15. "Machine gun"
   + 14.16. Brake system
   + 14.17. Wheels and tires

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14.8.6. Pistons


The car engine sometimes compare to heart of the person. Really, it works constantly while the car moves. However, such comparison is not quite correct. After all heart, as well as any live organism, is continuous самовосстанавливается: in it constantly there are processes of dying off of old cages and replacement their new, young. That you will not tell in any way about the lifeless mechanism – about the automobile engine. It, despite all our diligence, wears out is almost irreversible. However intensity of such wear, an engine resource before major maintenance, as well as durability of all car as a whole, in many respects depend on that, how qualitatively it is made and is competently maintained.

The main details of the engine – pistons with piston rings, rods and cylinders are especially subject to wear. Operation of pistons of the engine most impresses. After all, moving the returnable it is forward between the top and bottom dead points, they cover huge distance. So, at frequency of rotation of a cranked shaft of 5000 rpm and a piston stroke in 75 mm the total way of the piston in a minute makes 375 m. For a business hour this distance will be already 2 km of 250 m, and for a month of operation for 8 hours in day, excepting days off, the piston will move on 460 km. At a hard work of the car in 5 years (namely such duration of operation of the car before capital repairs is confirmed by statistics) the piston will cover distance in 24 000 km!

So, wear of the piston and the details interfaced to it is inevitable. However sizes of wear of piston groups (pistons – piston rings) before major maintenance of engines of various firms very differ from each other. So, limiting wear of pistons and piston rings of engines Mercedes-Benz, Volkswagen, BMW, the majority of the American and Japanese firms comes after run about 300 000 km. At the same time engines of others, say, less perfect models, need replacement of pistons and piston rings after 50 000 km of run (almost in 10 times less!).

In what here reason? And how the durability of these details depends on service conditions? For the answer to these questions we will consider two typical designs of piston groups of the petrol engine and a diesel engine. Let's remind, first of all, that pressure of gases in cylinders of these engines at the beginning of a working course differs approximately twice. In the carburetor engine or in the engine with direct injection of gasoline it makes 4055 kg/cm2, in a diesel engine is 70–80 kg/cm2. Therefore also pistons of petrol and diesel engines differ one from another though the main constructive decisions at them are identical.

The typical piston of the carburetor engine is cast from an aluminum alloy and covered outside with a tin layer for prirabatyvayemost improvement to a cylinder mirror. Its top part – a head – has smaller on 0,1 mm diameter, than internal diameter of the cylinder. It is made for prevention of jamming of a head in the cylinder at a warming up. In ring flutes two are placed kompressionny and one maslosjemny ring. The lower part of the piston – a skirt – in cross-section section is oval, and on height has a conic form: in the top part – smaller diameter, than in bottom. Besides, in piston lugs with openings under a piston finger вплавлены two steel thermoregulating inserts. All this is made for prevention of increase in a friction between a skirt and a cylinder mirror when heating piston. Having smaller, than at aluminum, factor of thermal expansion, these inserts pull together a skirt in the direction, perpendicular axes of a piston finger.

Opening under a piston finger in modern engines usually displace from a symmetry axis to the right side of the engine. For the correct assembly of the piston with a rod and their installations in the engine cylinder about an opening of a lug there is a label which should be turned towards a forward part of the engine. Such shift do for reduction of lateral making pressure force of the gases pressing the piston to one of the parties of the cylinder on a step "a working course".

The rod also should be correctly сориентирован in the engine. On its forward party is available openings for the directed stream of oil on the loaded party of a mirror of the cylinder (in some engines this opening is absent). Loose leaves and a cover of the bottom head of a rod also have the corresponding labels for the correct assembly. Its further working capacity and durability essentially depends on accuracy of manufacturing of the piston and its true selection to a cylinder opening. Leading avtomobilestroitelny firms apply today system according to which pistons on external diameter are broken usually into five or six classes through 0,01 mm. Besides, they разелены on 3–4 categories through 0,004 mm according to diameter of an opening under a piston finger. Engine cylinders also have similar division into five classes. Such system allows to pick up most precisely the piston of the corresponding class to any, even to the worn-out cylinder, and a finger of the necessary category to an opening in lugs and to a rod. For major maintenance of the engines, consisting usually in boring of cylinders, firms let out repair pistons of the increased sizes.

The piston of a modern diesel engine is calculated on perception of more high pressures therefore it has big thickness of the bottom and lugs. Besides, the design of the piston of a diesel engine differs from considered earlier a little. The main difference is placement of the chamber of combustion directly in a piston head. As combustion occurs when finding the piston near the top dead point, hot gases heat up a piston head more strongly, and walls of the top part of the cylinder heat up rather less, than in petrol engines. For reliable consolidation of the piston in the cylinder on its external surface five flutes under piston rings are made. In three top flutes kompressionny rings are established. In the bottom flutes two maslosjemny rings are placed. Many firms make kompressionny rings of rectangular section, practically nothing different from rings of petrol engines. However more progressive, though more darling is a design with a konusny top working surface. A tilt angle forming a cone at such rings do usually 10 °. Application of konusny rings provides some increase in their durability as on a step "a working course" the component of pressure force of gases on a konusny surface of a ring in addition presses it to a cylinder mirror. Feature of service and repair of pistons with konusny kompressionny rings is exact control of gaps. Gaps between a flute and maslosjemny rings supervise as well as in petrol engines.

Forces of a friction between surfaces of a skirt of the piston and a cylinder mirror at diesel engines are higher, than in petrol engines. For increase in durability at a surface of a skirt of pistons in modern firms put a layer of a special colloidal and graphite covering. It much more improves a piston prirabatyvayemost to the cylinder and extends term of its work before major maintenance. Similar processing of rubbing surfaces of pistons apply today and on petrol engines.

Except wear of surfaces of a skirt, flutes under kompressionny rings of the piston wear out also. The flute under a maslosjemny ring, though such wear usually Besides, wears out much less. At wear of flutes of a ring start to move more and more intensively down and up on flute height, and more and more notable there is a so-called pump action of rings. It is shown in more and more increasing consumption of karterny oil of the engine. Getting to the combustion chamber, it burns down there, forming the gray smoke leaving an exhaust pipe of the car. At considerable wear of flutes replacement of rings on new improves a situation a little. There comes objective need for replacement of all piston group with very desirable boring of cylinders for the repair size. All described types of wear is natural and, unfortunately, inevitable process.

It is possible to fight against natural wear of the engine successfully, prolonging its working capacity. America here it is not necessary to open. It is just necessary to fulfill scrupulously requirements for car operation, to use qualitative oil and oil filters, competently to regulate fuel equipment. Use of high-quality modifiers of oil and fuel, the preparations changing a microstructure of blankets of a friction of engines gives good results.

Along with it wear of the engine, as well as all car as a whole, in many respects depends on the driver, from his qualification and technical literacy. After all not for nothing cars of the same brand at one drivers serve long and smoothly, at others – are under repair almost every week. The skilled driver almost never allows operation of the engine with an overload, and furthermore – a detonation. He constantly listens, as its engine works, and immediately reacts to the overload accompanied by a booming, low-voice-frequency sound on lowered frequency of rotation of a cranked shaft. The mode of dispersal of the car also is accompanied by the increased wear of the engine. The analogy to a horse and the equestrian here arises: the careful owner without special need will not whip the canine friend, forcing it to run straight away, especially when the horse was not warmed up yet. Certainly, in critical situations the driver presumes dashingly, extremely sharply to disperse the car. But if such abrupt style of driving becomes a habit, engine repair at such reckless driver is for certain provided twice earlier, than it is provided by specifications.

Other type of wear not provided by any instructions is often observed also. It is emergency breakage of shatunno-piston group and, first of all, rings and crossing points of ring flutes of the piston. In petrol engines it is connected first of all with a detonation. Let's remind that the detonation is a vzryvopodobny combustion of gas mixture in the cylinder, accompanied by spasmodic increase of pressure in the combustion chamber. It is to equivalently sharp blow a weighty sledge hammer on the motionless piston and rings. Details, naturally, are not calculated on loading and can break, having damaged then sharp splinters a cylinder mirror. Detonation reasons a little. However main of them – this operation of the engine on gasoline with lower, than it is provided by specifications, octane number, and also an overheat and work on rich gas mixture. The skilled driver is obliged to hear detonation knocks at operation of the engine and immediately to reduce supply of fuel at dispersal, and then to eliminate the detonation reasons. A sound of a detonation are the high-voice-frequency metal clicks coinciding on frequency with turns of a cranked shaft. They can be hardly audible against other sounds of the working engine, especially – at slightly early ignition, and to vanish at absolutely insignificant reduction of supply of fuel (gas). Such hardly appreciable detonation testifies to correctly adjusted coal of an advancing of ignition. but happens and so that detonation knocks appear at once by pressing a gas pedal that is certainly inadmissible, and to continue movement in such mode equivalently to a razbivaniye a hammer of interiors of the engine.

Diesel engines are not so sensitive to change of composition of diesel fuel, though in them there are the troubles conducting to increased wear of details of krivoshipno-shatunny group. It, first of all, overheat of the engine and related reduction of viscosity of oil, especially, if it low quality. The increased wear can be a consequence and the wrong adjustment of the pump of high pressure, and deterioration of dispersion of fuel in combustion chambers because of violation of work of nozzles. And, certainly, a lot of things depends on the driver.

So, from all aforesaid it is possible to draw such generalized conclusions. The durability of your car, and no less than all vehicle as a whole, depends on two factors: from quality of manufacturing for which the manufacturing firm, and from level of technical operation for which the driver is finally responsible is responsible. It is necessary to remember it both upon car purchase, and by preparation and training of drivers.