BMW 3 Series E30

since 1983-1994 release

Repair and operation of the car

The car engine is compared sometimes to heart of the person. Really, it works constantly while the car moves. However, such comparison is not quite correct. Heart, as well as any live organism, continuously self-repairs: in it constantly there are processes of dying off of old cages and replacement their new, young. What you will not tell about the lifeless mechanism in any way – about the automobile engine. It, despite all our efforts, wears out is almost irreversible. However intensity of such wear, an engine resource before capital repairs, as well as durability of all car in general, in many respects depend on that, how qualitatively it is made and is competently operated.

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. Moving returnable progressively between the top and lower dead points, they cover huge distance. So, with a frequency of rotation of a bent shaft of 5000 rpm and a piston stroke in 75 mm the total way of the piston in a minute makes 375 m. For hour of work this distance will be already 2 km 250 m, and for a month of operation 8 hours a day, excepting days off, the piston will move to 460 km. At hard work of the car in 5 years (namely such duration of operation of the car before overhaul 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 capital repairs of engines of various firms very differ from each other. So, extreme wear of pistons and piston rings of engines Mercedes-Benz, Volkswagen, BMW, most the American and Japanese firms comes after the run about 300 000 km. At the same time engines of others, say, of less perfect models, need replacement of pistons and piston rings after 50 000 km of a run (nearly 10 times less!).

In what here reason? And how 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 the diesel. Let's remind, first of all, that pressure of gases in cylinders of these engines at the beginning of the working course differs approximately twice. In the carburetor engine or in the engine with direct injection of gasoline it makes 40-55 ^kg/cm2 in the diesel - it 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 aluminum alloy and covered outside with a tin layer for improvement of a prirabatyvayemost to a cylinder mirror. Its top part – a head – has diameter, smaller on 0,1 mm, 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 are placed two compression and one oil scraper ring. The lower part of the piston – a skirt – in cross section is oval, and on height has conical shape: in the top part – smaller diameter, than in lower. Besides, in piston lugs with openings under a piston finger of a vplavlena two steel temperature-controlled inserts. All this is made for prevention of increase in friction between a skirt and a mirror of the cylinder when heating the piston. Having smaller, than at aluminum, coefficient of thermal expansion, these inserts pull together a skirt in the direction, perpendicular axes of a piston finger.

The opening under a piston finger in modern engines is usually displaced 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 tag which has to be turned towards a forward part of the engine. Such shift is done for reduction of a side component of the pressure force of gases pressing the piston to one of the parties of the cylinder on a step "the working course".

The rod also has to be correctly oriented in the engine. On its forward party is available openings for the directed oil stream on the loaded party of a mirror of the cylinder (in some engines this opening is absent). Inserts and cover of the lower head of a rod also have the corresponding tags for the correct assembly. Its further working capacity and durability significantly depends on the accuracy of production of the piston and its right selection to a cylinder opening. The leading automobile building firms apply today system according to which pistons on outer diameter are broken usually into five or six classes through 0,01 mm. Besides, they are razelena 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 worn-out cylinder, and a finger of the necessary category to an opening in lugs and to a rod. For capital repairs of engines, consisting usually in boring of cylinders, firms release repair pistons of the increased sizes.

The piston of the modern diesel is calculated on perception of more high pressures therefore it has the big thickness of the bottom and lugs. Besides, the diesel piston design differs from a little considered earlier. The main difference is placement of the combustion chamber directly in a piston head. As combustion happens when finding the piston near the top dead point, hot gases heat a piston head stronger, 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 compression rings are established. In the lower flutes two oil scraper rings are placed. Many firms make the compression rings of rectangular section almost not different from rings of petrol engines. However more progressive, though more expensive, the design with a conical top working surface is. The tilt angle forming a cone at such rings is done usually 10 °. Application of conical rings provides some increase in their durability as on a step "the working course" the component of pressure force of gases on a conical surface of a ring in addition presses it to a cylinder mirror. Feature of service and repair of pistons with conical compression rings is exact control of gaps. Gaps between a flute and oil scraper rings control as well as in petrol engines.

Friction forces between surfaces of a skirt of the piston and a mirror of the cylinder at diesels 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 the term of its work before capital repairs. Similar processing of the rubbing surfaces of pistons is applied today and on petrol engines.

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

Reference

It is possible to fight against natural wear of the engine successfully, prolonging its working capacity. Here it is not necessary to discover America. It is just necessary to fulfill scrupulously requirements for operation of the car, to use qualitative oil and oil filters, to competently adjust the fuel equipment. Good results are yielded by use of high-quality modifiers of oil and fuel, the medicines changing a microstructure of blankets of friction of engines.

Along with it wear of the engine, as well as all car in general, in many respects depends on the driver, on his qualification and technical literacy. Not for nothing cars of the same brand at one drivers serve long and smoothly, at others – are under repair nearly 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 with a booming, low-voice-frequency sound at the lowered frequency of rotation of a bent shaft. The mode of dispersal of the car is also followed by the increased wear of the engine. Here analogy to a horse and the equestrian 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 yet. Of course, in critical situations the driver is able to afford dashingly, extremely sharply to accelerate the car. But if such abrupt style of driving becomes a habit, repair of the engine at such reckless driver is for certain provided twice earlier, than it is provided by specifications.

Also another is often observed, the type of wear which is not provided by any instructions. It is emergency breakage of conrod and 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 the explosion-like combustion of gas mixture in the cylinder accompanied with spasmodic increase in pressure in the combustion chamber. It to equivalently sharp blow by 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 during the operation of the engine and to immediately reduce supply of fuel at dispersal, and then to remove the detonation causes. A sound of a detonation are the high-voice-frequency metal clicks coinciding on frequency with turns of a bent shaft. They can be hardly heard against the background of 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 noticeable detonation testifies to correctly adjusted ignition advancing coal. but happens and so that detonation knocks appear at once when pressing the accelerator pedal that, of course, inadmissibly and to continue the movement in such mode it is equivalent to dissecting by the hammer of interiors of the engine.

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

So, from all aforesaid it is possible to draw such generalized conclusions. Durability of your car, and as well as all vehicle in general, depends on two factors: from quality of production for which the manufacturing firm, and from the level of technical operation for which, eventually, the driver is responsible is responsible. It is necessary to remember it both upon purchase of the car, and by preparation and training of drivers.