BMW 3 series E30

Since 1983-1994 of release

Repair and car operation

14.20. Bearings of engines

THE GENERAL DATA

What bearings are established in your engine? Not all motorists answer such question intelligibly. One person far from technics has told directly: "Here ten years I go, instead of I know that there is inside".

Nevertheless bearings there are. And not any, but quite defined. They are durable, but are not eternal, and when fail, without understanding of an essence of the matter not to manage. Well, and for professionals-repairmen it simply an ordinary matter.

As the bearing works

Sliding bearings almost exclusively serve in modern automobile engines as support for cranked and camshafts. Bearings качения (ball, roller, needle) apply to the similar purposes only in small motorcycle motors.

Necessary working capacity of bearings of sliding is reached by use of so-called effect of an oil wedge. At rotation of a smooth shaft in a backlash between shaft and an aperture oil moves. As the loading operating on a shaft, causes its excentric displacement, oil is as though tightened in a narrowed part of a backlash and forms the oil wedge interfering contact of a shaft with walls of an aperture. The more pressure and viscosity of oil in a backlash, the the big loading (before contact of surfaces) maintains the sliding bearing.

Actual pressure of oil in a wedge zone reaches 50–80 МПа (500–800 kg/sm²), and in some designs and it is more. It in hundreds times above, than in submitting system. However it is not necessary to think that pressure of giving influences bearing work a little. The it is more, the there is an oil prorolling through the bearing more intensively and the its cooling is better.

Under certain conditions the operating mode with the minimum friction (it also name liquid) can be broken. It happens at понижениее to viscosity of oil (for example, because of its overheat owing to insufficient giving) and decrease in frequency of rotation at loading increase.

Quite often, especially after engine repair, not optimum geometry of knot affects also. At an insignificant deviation of the form of surfaces from cylindrical, at a warp of axes and other defects of details probably local increase of specific loading (that is the loading carried to the area of a surface) above an admissible limit. Then the oil film in these parts becomes thin, and shaft and bearing surfaces start to adjoin on microroughnesses. There is the mode of semiliquid greasing characterised by increase of a friction and a gradual warming up of the bearing. Further it can lead to a so-called boundary friction with full contact of the surfaces the overheat, схватывание (teases), jamming, fusion and bearing destruction will be which consequence.

It is clear that in operation the mode of a boundary friction is unacceptable. Nevertheless it appears at infringement of giving of oil, and it occurs because of its shortage in картере, that is or owing to oversight of the driver, or at pallet damage картера as a result of arrival on an obstacle more often.

The mode of semiliquid greasing is admissible only for short time when he has not time to affect deterioration of the bearing. An example – start-up of the cold engine. However, here there is other danger: at very low temperature oil можеты to be too viscous and its normal giving is restored long (20–30 seconds and more). Here already semiliquid greasing is capable to affect deterioration of details considerably.

Perfection of automobile engines is connected with constant growth of frequency of rotation and capacity increase. Increase of compactness of designs, including reduction of width and diameter of bearings is simultaneously observed. It means that specific pressure grow in knot. And as loading on the bearing at engine work cyclically changes on size and a direction, there is real a so-called fatigue failure of details. To provide working capacity of bearings in such conditions, special designs, materials and technologies are required.

As it is arranged

Usually bearings of cranked shaft in modern engines carry out in the form of thin-walled loose leaves or plugs in the thickness of 1,0-2,5 mm (it is rare more). Loose leaves of radical bearings of a cranked shaft do more thickly because of necessity to place a circular flute for oil giving to шатунным to bearings. The general tendency – reduction of a thickness of loose leaves which now averages 1,8-2,0 mm at radical and 1,4–1,5 mm at шатунных bearings. The loose leaves are more thin, the is better they adjoin to a surface of the case (bed), the better a heat-conducting path from the bearing, the geometry, a less admissible backlash and noise at work is more exact, it is more knot resource.

That at installation in bed the loose leaf has precisely accepted its form, in a free condition it should have a tightness on diameter of bed (so-called straightening) and not cylindrical form of variable radius. Besides, for good прилегания to a surface and deduction from проворачивания the tightness is necessary and on length of the loose leaf – it name выступанием. All these parametres depend on a thickness, width and diameter of loose leaves, thus straightening averages 0,5–1,0 mm, and выступание – 0,04–0,08 mm. However and it still it is not enough for reliable work of the bearing. About a socket a thickness of loose leaves reduce by 0,010–0,015 mm to avoid задиров in these parts. They can appear because of aperture deformation in the case under the influence of working loading when the working backlash in the bearing is small.

Materials for loose leaves can be different. Their choice co-ordinates with a material of a cranked shaft and its heat treatment, degree форсировки the engine and the set resource. To a certain extent affect here and traditions of automobile firm.

Loose leaves always do multilayered. A loose leaf basis – a steel tape which provides durability and reliability of landing in the case. On a basis in the various ways put a layer (or layers) a special antifrictional material in the thickness of 0,3-0,5 mm. The basic requirements to an antifrictional material – a low friction on a shaft, high durability and heat conductivity (that is from a surface heat is good to spend to the bearing case ability). The first requirement is better provide soft metals, for example, alloys with the big maintenance of tin and lead (in particular, widely known баббиты).

In the past баббиты were widely applied on малофорсированных низкооборотных engines. With growth of loadings durability of such loose leaves with a thick layer баббита has appeared insufficient. The problem has been solved by replacement of all this layer by an original sandwich – свинцовооловянистую the bronze covered thin (0,03–0,05 mm) a layer of the same баббита. The loose leaf became multilayered. In modern engines "сталебронзобаббитовые" loose leaves usually carry out 4-layer (under баббитом very thin intermediate layer of nickel still lies) and even 5-layer when for improvement extra earnings from above the most thin layer of tin is put on a working surface. So bearings on many foreign engines look.

Along with it the wide circulation was received also by steel-aluminium loose leaves. As an antifrictional material alloys of aluminium with tin, lead, silicon, zinc or cadmium, both with coverings, and without them here serve. Most often in world practice the alloy of aluminium from 20 % of tin without a covering is used. It well resists to high loadings and speeds of rotation of modern engines, including diesel engines, and simultaneously possesses satisfactory "softness". Nevertheless steel-aluminium loose leaves are more rigid, than баббитовые (or with баббитовым a covering), therefore are more inclined to teases in the conditions of insufficient greasing.

Auxiliary and camshafts of engines rotate, as a rule, with smaller frequency, than cranked and test much smaller loadings, therefore it is easier than a condition of their work. Loose leaves and plugs of these shaft usually do of the materials, similar by the aforesaid. Besides, here sometimes apply баббит or bronze without a covering. Frequently these bearings at all have no plugs or loose leaves and are formed directly растачиванием apertures in a head of the block of cylinders. In such designs the head is executed from an alloy of aluminium with silicon which possesses quite good antifrictional properties.

The general for bearings of modern engines, especially if it is a question of support of cranked shaft, conformity of a material and a design of loose leaves to a material and shaft working conditions (frequency of rotation, loading, a greasing condition etc. is.). Therefore any replacement of details when, for example, at repair put loose leaves from other engine, cannot be recommended. Otherwise the durability of the repaired unit can appear very small. To dare at such step, it is necessary to have the corresponding information.

Loose leaves are very exact (прецезионные) details. To guarantee small (but quite concrete – on the average 0,03–0,06 mm) working backlashes in bearings, at manufacturing a thickness of the loose leaf maintain with accuracy of an order 5–8 microns, and length – 10–20 microns. Infringement of these requirements can lead to change of a working backlash in the bearing or density of landing of the loose leaf in the case that is inadmissible because of decrease in reliability and a resource of all engine as a whole.

Who makes them

Complexity of all circle of the problems connected with creation of high-quality automobile bearings of sliding, has led to that their manufacture has gradually passed to specialised firms. Abroad many their such firms simultaneously let out also other details of engines, and deliveries go both on conveyors of car factories, and to spare parts. Some firms such are a part of known transnational industrial and commercial and industrial corporations. From world manufacturers of bearings for engines it is necessary to note first of all firms Kolbenschmidt (KS), Glyco, TRW, Sealed Power, Glacier, Clevite, Bimet. Last years bearings have started to do and such firms – "coryphaeuses", as Mahle and Goetze. Among "young" it is necessary to mention the specialised firm King (Israel) which has begun release of bearings in the early eighties.

The majority of the listed manufacturers lets out the huge nomenclature of bearings and delivers the production in spare parts everywhere, including on our market (through dealers or the wholesale trading companies). Basically, of course, it is bearings for foreign engines – European, Japanese and American.

It is possible to find loose leaves in sale both standard, and the various repair sizes (as a rule, no more than 0,75 mm) on the majority of widespread models "Audi-folksvagen", the BMW, "Mercedes", "Ford", "Opel", "Fiat", "Tojota", "Nissan", "Mitsubisi", "Mazda" etc. On less widespread models, and also in need of purchase of loose leaves большего the repair size usually it is necessary to make out the order and to wait on the average for 5-10 days (at different trading firms these terms are various).

Quality of such production usually does not cause doubts neither on geometry, nor on materials. Though, if there is a choice and doubts in to what firm-manufacturer to prefer, it is necessary to mean the following. Such firms as, for example, Kolbenschmidt, Glyco, Glacier are one of the basic suppliers of mass production. At purchase of their products it is possible even to receive the same loose leaves that stood on the engine "since a birth". The difference will be only in absence on new details of an emblem of firm-manufacturer of the car. By the way, search "native" (or so-called original) loose leaves of the repair sizes can appear problematic. Not all automobile firms deliver repair loose leaves in spare parts, and the price of loose leaves in "original" packing, as a rule, considerably above, than directly from their manufacturer.

Loose leaves of other, less eminent firms are usually cheaper, though on quality to find out differences difficultly. Moreover, if there is a choice here it is possible to try to consider and car service conditions. So, rather cheap loose leaves, strangely enough, resist to bad quality oils and маслофильтрам, "walking" on our shops and the markets, than more expensive сталебронзобаббитовые is slightly better. It use practice under repair steel-aluminium loose leaves of firm "King" instead of regular бронзобаббитовых, in particular, has shown – such replacement does not put a damage of reliability of engines, but allows to save considerably.

Some of the listed firms let out loose leaves and for our cars. In our market it is already possible to find these products for engines VAZ of manufacture of firms Clevite, Bimet and Glacier. Certainly, they aloud are more expensive than the domestic. However to save on loose leaves at repair of domestic motors it is not necessary. Comparison with import production domestic usually does not maintain. Deviations on a thickness at some our commodity copies reach 25–30 microns instead of 8 microns, regulated by the admission. As a result after зажатия a cover внутрення the bearing surface gets the wrong form at which, for example, the backlash in 0,07–0,09 mm in one section of the bearing can even pass in a tightness in other.